inno ts/rs e 15.qxd 15.08.2005 10:35 uhr seite iii innovation … abbe.pdf · 2006. 1. 3. · the...

InnovationT h e M a g a z i n e f r o m C a r l Z e i s s

In Memory of Ernst Abbe

ISSN 1431-8059

15

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Innovation 15, Carl Zeiss AG, 20052

Contents

Editorial

Formulas for Success. . . ❚ Dieter Brocksch 3

In Memory of Ernst Abbe

Ernst Abbe 4Microscope Lenses 8Numerical Aperture, Immersion and Useful Magnification ❚ Rainer Danz 12Highlights from the History of Immersion Objectives 16From the History of Microscopy: Abbe’s Diffraction Experiments ❚ Heinz Gundlach 18The Science of Light 24Stazione Zoologica Anton Dohrn, Naples, Italy 26Felix Anton Dohrn 29The Hall of Frescoes ❚ Christiane Groeben 30Bella Napoli 31

From Users

The Zebra Fish as a Model Organism for Developmental Biology 32SPIM – A New Microscope Procedure 34The Scourge of Back Pain –Treatment Methods and Innovations 38ZEISS in the Center for Book Preservation ❚ Manfred Schindler 42

Across the Globe

Carl Zeiss Archive Aids Ghanaian Project ❚ Peter Gluchi 46

Prizes and Awards

100 Years of Brock & Michelsen 48Award for NaT Working Project 49

Product Report

Digital Pathology: MIRAX SCAN 50UHRTEM 50Superlux™ Eye Xenon Illumination 50Carl Zeiss Optics in Nokia Mobile Phones 51

Masthead 51

Inhalt_01_Editorial_E.qxd 15.08.2005 9:07 Uhr Seite 2

It clearly and concisely describes the resolution of opticalinstruments using the visible spectrum of light and con-tributed to the improvement of optical devices.

The same year also saw the passing of another Germanmicroscope manufacturer with connections to Abbe andZeiss: Rudolf Winkel (1827-1905). During Abbe’s times,good microscopes were also built at Winkel’s workshopwhich was founded in Göttingen in 1857. Abbe visitedWinkel’s workshop while he was a student in Göttingen.His visit in 1894 led to closer cooperation. In 1911, Zeissbecame Winkel’s chief partner. In October 1957, the firm R. Winkel GmbH became part of the Carl ZeissFoundation.

The same year that Abbe died, Robert Koch (1843-1919) received the Nobel Prize for Medicine for his exam-inations and discoveries while researching tuberculosis. In1878, Robert Koch used the Abbe oil immersion systemfor the first time and was impressed by the “quantumleap“ made by the “Carl Zeiss Optical Workshop usingProfessor Abbe’s ingenious advice.“ In 1904, Carl Zeissmanagement presented Robert Koch with the 1000th

1/12 objective lens for homogenous oil immersion.Many articles in this issue are dedicated to Ernst Abbe

and his times. We reflect on what Ernst Abbe meant toCarl Zeiss and what he did for optics, and we take a spe-cial look at developments that were and continue to besignificantly influenced by Ernst Abbe and his scientificresults. This is emphasized by the image on the coverpages: an historical tribute to the more than 150 years ofoptical development with a focus on microscopy.

July 2005

Dr. Dieter Brocksch

ScientistEntrepreneur

Social Reformer

Formulas describe the functions and processes of whathappens in the world and our lives. It is often the small,insignificant formulas in particular that play a decisiverole in what we know and in the functionality of moderninstruments and examination methods.

for the large. . .

The fiftieth anniversary of the death of Albert Einstein(1879-1955) also marks the centennial of his theory ofrelativity; a theory that revolutionized perceptions, madethe processes of life more understandable and began toexplain the dimensions of time and space. The short for-mula, E = m · c2, expresses the infinite complexity of ourworld. Einstein had contact with Zeiss throughout thecourse of his scientific activities. In 1925 he wrote to thecompany Anschütz in Kiel about producing a gyrocom-pass: “The difficulties of manufacturing are so great –accuracies of 10-4 have to be achieved – that Zeiss iscurrently the only company capable of meeting the re-quirements.“

. . . and small things in life.

2005 also marks the 100th anniversary of the death ofErnst Abbes (1840-1905). Numerous events throughout2005 honor his many great achievements. His extensiveexaminations within the scope of his activities at CarlZeiss’ optical workshop also resulted in the formula forthe resolution of a microscope:

Formulas for Success...

3

Ed i tor ia l


d =�

2n sin �

Inhalt_01_Editorial_E.qxd 15.08.2005 9:07 Uhr Seite 3


Education and early years

Ernst Abbe was born in Eisenach onJanuary 23, 1840, as the son ofmaster spinner and subsequent fac-tory attendant Georg Adam Abbeand his wife Christina. He attendedelementary school from 1846 to1850, after which he was a studentat the local high school in Eisenach.He finished his school education in1857 and graduated with above-average grades. In the period to1861 he studied mathematics andphysics at the Universities of Jena

cine and Science, in which he gave atotal of 45 lectures in the period to1895. From 1866, he was a freelancescientist with the court and universitymechanic Carl Zeiss in Jena. In 1870Abbe formulated the famous sinecondition subsequently named afterhim, a condition that must be met byany spherically corrected lens if it isalso to be free from coma in the neighborhood of the lens axis inmicroscope image formation. In thesame year he became an extraor-dinary professor at the University ofJena. On September 24, 1871, hemarried Elise Snell, the daughter of lec-turer Prof. Snell, a mathematics andphysics lecturer at the University ofJena. Three years later, the first child,his daughter Paula, was born. His fa-ther died on August 18, 1874. Abbewas director of Jena Observatoryfrom 1877 to 1900. On May 1, 1878,he was appointed as an honorarymember of the London Royal Micro-scopical Society. In June of the sameyear, he became an ordinary hon-orary professor at the University ofJena. He was awarded the title of Dr.

In Memory of E rns t Abbe

(1857-1859) and Göttingen (1859-1861). Abbe completed his studies byobtaining his doctorate in Göttingenon the subject “Experiential substan-tiation of the theorem of equivalencebetween heat and mechanical ener-gy“. He subsequently worked for twoyears as a teacher at the PhysicsAssociation in Frankfurt/Main.

Family andscience

Abbe’s mother died early in his life:July 14, 1857. During his studies, hisfather married for the second time, tothe widow Eva Margarethe Liebetrauon November 11, 1859. After histime in Frankfurt, Abbe joined theMathematical Association in Jena in1863. In the same year, he obtainedhis post-doctoral qualification as alecturer with his paper on “the lawsin the distribution of errors in obser-vation series“. He taught as a privatemathematics and physics lecturer atthe University of Jena.

In 1863 Abbe also became a mem-ber of the Jena Association of Medi-

1857

In 2005, the book titled “ErnstAbbe – Scientist, Entrepreneurand Social Reformer” waspublished by Bussert & Stadeler, Jena Quedlinburg to mark the 100th anniversaryof Ernst Abbe’s death.

[ISBN 3-932906-57-8]

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5Innovation 15, Carl Zeiss AG, 2005

for Otto Schott in Jena. The followingyear saw the signing of the new part-nership agreement in which Abbebecame an active partner togetherwith Carl and Roderich Zeiss.

In 1884 the Glastechnische Labo-ratorium Schott & Gen. (later to be-come Jenaer Glaswerk Schott &Gen.) was founded by Otto Schott,Ernst Abbe, Carl Zeiss and RoderichZeiss.

In search of calcium fluoride foroptical applications, Abbe traveled toOltscherenalp in Switzerland for thefirst time in 1886. After the death ofCarl Zeiss on December 3, 1888,Abbe became the sole owner of theZeiss works in 1889. At the sametime, he discontinued his teachingactivities at the University of Jena.From 1890 onwards, Abbe expandedthe product spectrum on an ongoingbasis: measuring instruments (1890),camera lenses (1890), binoculars(1894), astronomical instruments(1897) and photogrammetric instru-ments (1901). As a result, the num-ber of employees rose to over 2000by 1905.

med. h. c. by the University of Hallein 1883 and the title Dr. jur. h. c. bythe University of Jena in 1886. In1900 Abbe became a correspondingmember of the Imperial AustrianAcademy of Science in Vienna. In1901 he was appointed as an hon-orary member of the Saxon Academyof Science and of the Academy ofScience in Göttingen.

Abbe as an entrepreneur

The process of integrating scienceinto industry already started in the1860s. In addition to Carl Zeiss,Siemens and Bayer were also pio-neers of this development. By hiringscientific staff, Ernst Abbe was adecisive driving force behind thisprocess at Zeiss: the integration ofR&D into the company was an impor-tant step toward technology leader-ship. The training of capable employ-ees and successors also played asignificant role in the entrepreneurialand commercial areas. Competentstaff and constant quality control

allowed the implementation of highquality standards. The corporate or-ganization was successfully focusedon growth by the clear allocation ofresponsibilities for scientific, technicaland commercial staff.

From 1872, all ZEISS microscopeswere built in line with Abbe’s calcula-tions. Three years later, in 1875,Abbe became a dormant partner inthe Optical Workshop of Carl Zeiss.Abbe pledged not to increase his ac-ademic activity beyond the currentmeasure and not to accept a profes-sorship in Jena or elsewhere. Oneyear later, he traveled to London toattend the international exposition ofscientific instruments on behalf ofthe Prussian Department of Educa-tion. In 1878, due to his obligationsat Zeiss, he turned down the offer ofa post as professor in Berlin instigat-ed by Hermann von Helmholtz. Healso declined the offer of an ordinaryprofessorship in Jena.

He initially came into contact withDr. Otto Schott in 1879. Their collab-oration began one year later. In 1882a private glass laboratory was set up

18801863 1870 1875



Abbe’s persistence in his endeavorsto also provide other manufacturerswith new types of optical glass was of great help to the German opticalindustry. He was skeptical about thepatenting of products, which he saw as an obstruction to scientificprogress in general. Not until compet-itive pressure made it unavoidable didthe patenting of camera lenses andbinoculars begin. However, his earlypioneering work remained accessiblefor general use. With the aid ofAbbe’s comparator principle, instru-ments for the highly accurate meas-urement of workpieces were pro-duced. These were important aids forinstrument construction in Germany.

Abbe retired in 1903. To mark thisoccasion, a torchlight procession tookplace with 1500 employees of theFoundation companies. Two yearslater, Ernst Abbe died on January 14,1905, after a long, serious illness.

Abbe the socialreformer and the Carl Zeiss Foundation

Many companies introduced theirsocial policy in the late 19th century.

the constitution also reflected Abbe’ssocial commitment. For example, acouncil was set up to represent theinterests of employees. Although thiscould not be seen as codeterminationin the modern sense of the term, itdid entitle the representatives tovoice their opinion in all matters con-cerning the enterprise. Paid vacation,profit sharing, a documented entitle-ment to pension payments, contin-ued pay in the event of illness and,from 1900, the eight-hour workingday were further social milestones.This all made the Foundation enter-prises Carl Zeiss and SCHOTT fore-runners of modern social legislation.

Tolerance was central to ErnstAbbe’s basic philosophy of life. Al-though he was certainly not a socialdemocrat, it was important to himthat this political party was able toevolve and develop freely. He wasalso vehemently against racism, aphenomenon which was alreadyprevalent during his times. He en-sured that no-one at Carl Zeiss suf-fered in any way due to their origin,religion or political affiliation. Thisattitude was reflected in the fact that two of his closest management

As a reformer, Abbe was far ahead ofhis times with his socio-politicalideas. In 1889, in order to safeguardthe existence of the enterprises CarlZeiss and SCHOTT irrespective of per-sonal ownership interests, Abbe setup the Carl Zeiss Foundation whichhe made the sole owner of the Zeissworks and partial owner of theSCHOTT works in 1891. In the sameyear, Abbe transferred his industrialassets to the Carl Zeiss FoundationWith the appropriate compensation,Roderich Zeiss also transferred hisshares to the Foundation, making itthe sole owner of the firm Carl Zeissand partial owner (sole owner from1919) of Jena Glaswerk Schott &Gen. Until 1903, Abbe was the au-thorized representative and one ofthe three directors of the Carl ZeissFoundation. The corporate statute ofthe Foundation came into force in1896. The first supplementary statutefollowed just four years later.

With his corporate statute of1896, Abbe gave the enterprise aunique constitution. In addition to itsexceptionally progressive stipulationsconcerning corporate managementand legally anchored labor relations,

Global Player

As many as 100 years ago, Carl Zeiss was alreadywhat would now be called a global player: the firstsales branches were founded in London (1894),Vienna (1902) and St. Petersburg (1903). Today, thecompany has 15 production facilities in Germany,USA, Hungary, Switzerland, Mexico, Belarus and China as well as 35 sales organizations and 100 agencies across the globe.

special

1888 1901



colleagues, Siegfried Czapski andRudolf Straubel, were Jewish citizens.

Promoter of scienceand research

Abbe always attached great impor-tance to the promotion not only ofscience and research, but also of cul-ture. As a private citizen, Abbe sup-ported the university with anony-mous donations. The university andthe city of Jena were both sponsoredby the Carl Zeiss Foundation after itscreation. As early as 1886, the pro-motion of science and research be-gan with the secret “endowmentfund for scientific purposes“.

Shortly after the development ofthe new microscopes, decisivebreakthroughs were made in thefield of bacteriology. In 1904Robert Koch wrote: “I owe a largeproportion of the success I haveachieved for science to your excel-lent microscopes”. In the decadesbefore the First World War medicalresearch in Germany had a worldstanding that was paralleled onlyby the reputation enjoyed by ZEISS instruments. Emil Behring inthe field of serology or Paul Ehrlichin the field of chemotherapy areonly two examples of many. Need-less to say, their success was notattributable to their instrumentsalone, but the microscopes did playan important role. The firm CarlZeiss also created products for thefield of chemistry, some of whichwere customized solutions: the gasinterferometer for Fritz Haber, forexample.

Products for Science

special

1905



duced a new lens combination – itconsisted of two plano-convex lenseswith a stop in the middle. Sir DavidBrewster’s (1781-1868) idea of man-ufacturing objective lenses from dia-monds was implemented in 1824 byAndrew Pritchard. Brewster recom-mended using oil immersion to se-cure achromatism in 1813. In 1816,Joseph von Fraunhofer (1770-1841)produced the first achromatic lensthat could be used in microscopy. In1823, Paris based physicist Selliguecombined up to four achromaticcemented elements into one objec-tive – this was the breakthrough inthe manufacture of achromatic mi-croscope objectives with high resolu-tion.

In an age of increasing mecha-nization and the beginning of indus-trial manufacture, Carl Zeiss quicklyrecognized the link between theoryand practice, between science andproduction required to effectively

Figs 1-3:Early immerson objectives.

The quality displayed by earlymicroscope objectives was usuallyvery modest. The images wereslightly blurred. Producing a mi-croscope objective required a lotof hard, intricate work until wellinto the second half of the 19thcentury. The standard complextrial and error process needed toconstruct the optical systems wasextremely time consuming andthus expensive.

Sometime around 1810, Joseph Jack-son Lister (1786-1869) referred tothe connection between the angularaperture of the objective and theattainable resolution for the firsttime. Two years later, William HydeWollaston (1766-1828) improved theoptics of the simple microscope:using Wollaston doublets, he intro-

1 2 3

Microscope Objectives

ao

o

The Wollaston prism of the DICmicroscopy technique is namedafter him. Wollaston discoveredthe elements palladium andrhodium and was the first scien-tist to report about the darklines in the solar spectrum. His way of viewing the geo-metric arrangement of atomsled him to crystallography andto the invention of the moderngoniometer for the angularmeasurement of crystal sur-faces. In 1806 he invented theCamera lucida, an optical aidfor perspective drawing thatallows the observation of anobject on a drawing surface. In its basic structure, the Camera lucida is a glass prismwith two reflecting surfacesinclined at an agle of 135° thatgenerates the image of a sceneat right angles to the eye of the observer.

William Hyde Wollaston(1766-1828), English physicist, chemistand philospher.

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manufacture powerful instrumentsthat would be able to stand up to the pressures of competition. Zeisslooked hard for a solution. The initialattempts to compute microscope ob-jectives between 1850 and 1854 byhimself and his friend, mathematicianFriedrich Wilhelm Barfuss, however,did not return any noteworthy re-sults.

In 1866, Carl Zeiss approached ayoung, private tutor, Ernst Abbe, andrequested help in developing im-proved microscope objectives. Overthe next few years, Abbe developedthe new theory of microscope imageformation which is based on waveoptics (theory of diffraction) and waspublished in 1873. During this time,the sine condition for imaging, whichdefines the resolution limits of a mi-croscope, was also formulated. Usingthe new theory, Abbe calculated sev-eral new microscope objectives. Theconstruction of measuring devices

which are required for efficient pro-duction of objectives with consistent-ly high quality, finally enabled Abbeto produce objectives on a scientificbasis. He expanded the division oflabor and specialization of employeesthat Zeiss had started in the 1850s.Measuring machines and testing in-struments such as a thickness gages,refractometers, spectrometers andapertometer later entered volumeproduction.

In his early works, Abbe alreadyrecognized that microscope objec-tives would only be able to achievetheir full performance with the help

of new types of glass. This led Abbeto bring young glass maker OttoSchott to Jena in 1882. Two yearslater, Abbe and Zeiss became part-ners of the newly founded Glas-technische Laboratorium Schott &Genossen. The new Schott glass ma-terials enabled Abbe to construct theapochromatic objective – the mostpowerful microscope objectives of thelate 19th century – in 1886.

Fig. 4:Positive lens element.

Fig.5:Diagram showing imagegeneration.

Fig. 6:Negative lens element.

Fig. 7:Chromatic aberration.

Fig. 8:Spherical aberration.

d

f

R1R2

4

f

R1

R2

d

6

87

fS1 S2

f

5



Fig. 9:Natural (left) and artificial fluorite.

Reason for Abbe’strip to Switzerland

16 February 1889, lecture by Dr.Edmund von Fellenberg during ameeting of the Natural Research So-ciety in Bern, Switzerland: About theFluorite of Oltschenalp and its Techni-cal Utilization. “An historical, scientif-ic memorandum for later times”.

…In our Alps calcium fluoride orfluorite is no rarity and is quite fre-quently found in the area of pro-togine (gneiss granite), the varioustypes of gneiss and crystalline slateand sometimes with excellent color-ing and interesting crystal shapes…

In 1830, on a scree slope at thefoot of the Oltschikopf (2235 m) onthe Oltscheren mountain pasture,some Alpine enthusiasts discoveredfragments of a shining, spathicmineral of outstanding transparency that they naturally thought to berock crystal.…

…The mineral emerged fromoblivion again in the summer of1886. When visiting mineral inspec-tor B. Wappler in Freiberg (Saxony)during his search for water-clear fluo-rite, Dr. Abbe, professor of physics atthe University of Jena, had seenpieces of this material which Wapplerhad received from me in exchangefor minerals from Saxony many yearsbefore.

…Wappler indicated that he hadreceived the pieces from me andcorrectly stated that they had beenfound in the lower Haslithal in thecanton of Bern in Switzerland. Act-ing upon this information, ProfessorAbbe traveled immediately toSwitzerland to visit me. He showedme a piece of transparent fluoriteand asked me whether I could tellhim where this mineral could befound in Switzerland.

Source: Mitt. Naturf. Ges. Bern (1889)p.202-219

9



Fig. 10:The Alpine house in Bielen(Bühlen) on the OltscherenAlps in 1889. Ernst Abbe canbe easily recognized in theenlarged section producedby Trinkler in 1930 using thebest Carl Zeiss copyinglenses available at that time.

Calcium fluoride orfluorite (CaF2)

Fluorite is a mineral of the halogeni-des class. It is not only a populargem, but also an important raw ma-terial for the production of hydroflu-oric acid, fluorine and fluxing agents(e.g. for the manufacture of alumi-num) and for the etching of glass.Clear crystals are used as lens ele-ments for optical instruments. Nowa-days, artificially produced fluorite isused in optics. The name fluorite co-mes from the Latin word fluere (toflow) and resulted from the use ofthe mineral as a fluxing agent in theextraction of metals. Fluorite displaysthe colors purple, blue, green, yellow,colorless, brown, pink, black and red-dish orange. At the end of the 19th

century Ernst Abbe was the first per-son to use natural fluorite crystals inthe construction of microscope ob-jective lenses in order to enhancechromatic correction.

Oltscheren mountainpasture (1623 m)

Hut no. 86 with the inscription “B1873 H*: edifice on a solid founda-tion, with a kitchen-cum-living roomsince 1996; saddle roof with …,three-room living area facing NE onthe first floor (two rooms in thefront, behind them a now unusedkitchen and behind this a store andbarn. Beside these a milking installa-tion with 5 stands. The hut belongedto the Zeiss Works in Jena during the period when the company wasmining for fluorite.

10


Readers interested in mathematicsmight be surprised to see that Abbeused the sine instead of the tangentof half the angular aperture, as re-quired by Gaussian image formation,for example. The latter, however, isonly concerned with very narrow raypencils, i. e. the sines and tangents of the angular apertures are inter-changeable. After initial failures,Abbe quickly realized that a veryspecific condition must be met formicroscopic imaging, namely the sinecondition: if surface-elements are tobe imaged without error by means ofwidely opened ray pencils, the ratiobetween the numerical apertures onthe object and image sides mustequal the lateral magnification, andthus must be constant. If this condi-tion has been met and the sphericalaberration1) (aberratio [Lat.] = goingastray) corrected, the image is descri-bed as “aplanatic” (� – ��[Gr.] = not going astray); off-axisobject points are imaged without co-ma. Fig. 2 shows the 3-dimensional,almost error-free diffraction image ofan illuminated off-axis point (startest) that was captured with an ob-jective meeting the sine condition. Ifthe sine condition is not met, howev-er, the image cannot be aplanatic,but displays pronounced coma (Fig. 3).There is a fundamental relationshipbetween the sine condition and theresolving power: the angular separa-tion 2min of two separately visible

object points (the “weights” on thedumbbell-shaped object 2∆ymin inFig. 4) must measure at least

(3a)

since only then can the diffractionmaximum of the one object pointcoincide with the diffraction mini-mum of the other, and hence bothobject points can only just be seenseparately (diffraction at a circularpinhole or lens edge; the number1.22 is connected with the zeropoint of the Bessel function).

In the microscope, however, theresolution limit 2∆ymin (longitudinaldimension) and not the angular reso-lution is of prime interest. R. W. Pohlprovides an amazingly simple deriva-tion of the microscopic resolutionlimit from the sine condition:

In accordance with Fig. 4, formula(3a) can also be written as follows:

(3b)

According to Fig. 4, the numericalaperture on the image side can berepresented as follows:

n2 = 1.0 (air)

Coverslip,n1 = 1.518

Object(point) ofrefractive index nO

OP

2�1

2�2

1

2 3


Causal connectionbetween numericalaperture and resolution

The key parameter of a microscope isknown to be its ability to resolveminute object details, and not itsmagnification. To define the resolv-ing power and its reciprocal value,the limit of resolution, Ernst Abbecoined the term numerical aperture(apertura [lat.] = opening, numericalaperture = dimensionless aperture).The numerical aperture is the prod-uct of the refractive indexOR and thesine of half the angular aperture inthe object space, and has one deci-sive advantage over the sole use ofthe parameter “angular aperture =2�”: its behavior is not changed byrefraction at plano-parallel surfaces(e. g. coverslips).

Snell’s law of sines

(1)

Numerical Aperture, Immersion and Use

12

allows easy proof of this invariance(Fig. 1):

(2)

n1 · sin �1 = n2 · sin �2 = ... = ni sin �i

Fig. 1:Illustration of the invarianceof the numerical aperturewith regard to refraction at aplano-parallel glass plate (e. g. a coverslip).

n1 = 1.518 ,�1 = 40° ,n2 = 1.0 ,�2 = 77.4° ,

n1 sin �1 = n2 sin �2

Fig. 2:Large-aperture dry objective:the sine condition has beenmet (explained in the text).

Fig. 3:Same objective type: the sinecondition has not been met;off-axis image points displaypronounced coma(explained in the text).

(Figures 2 and 3 by courtesyof M. Matthä, Göttingen,Germany).

sin �1 =n2

sin �2 n1

1) (R.W. Pohl aptlydescribed sphericalaberration as “…poor combinationof axially symmetricallight bundles with awide opening...”)

sin2min =1.22 · �

d

2∆y’min = 1.22 · �

b d

INNO_06_numerisch_E.qxd 15.08.2005 10:19 Uhr Seite 12

n2 = 1.0 (air)

Objective front lens(e. g. BK 7,n3 = 1.518)

Homogeneousimmersion,n2 = 1.518 (oil)

Coverslip,n1 = 1.518

Object(point) ofrefractive index nO

1

2�

Dry objective Immersion objective2

OP

5

(4)

(In general, the image space is filledwith air, i.e. nBR = 1.0)

When the sine condition is taken intoaccount,

(5)

the smallest, still resolvable distancebetween two object points, i.e. theresolution limit 2∆ymin, is

(6)

The reciprocal value of (6) is de-scribed as resolving power, whichshould have as high a value as possi-ble.

The benefits of immersion

The fundamental resolution formula(6) valid for objects which are notself-luminous states that the resolu-tion limit depends on two factors,namely the wavelength � and the nu-merical aperture of the objective. If,therefore, the resolving power is tobe increased or the resolution limitminimized accordingly, shorter wave-lengths and a larger numerical aper-ture must be selected.

What should be done, however, ifa very specific wavelength or whitelight must be used and if, with nOR =1.0, the maximum value of 0.95, forexample, has already been allocatedto the dry aperture? In such cases,immersion objectives are used, i. e.objectives whose front lens immerses(immergere [Lat.]) into a liquid, theoptical data of which has been in-cluded in the objective’s computa-tion. In the special case of homoge-neous immersion, the refractive in-dices of the immersion liquid n2 andthe front lens n3 have been matchedfor the centroid wavelength2) in sucha way that the rays emitted by an ob-ject point OP (Fig. 5) pass the immer-sion film without being refracted andcan thus be absorbed by the frontlens of the objective. In this case, thenumerical aperture has been in-creased by the factor n2, i. e. thewavelength and therefore the resolu-tion limit has decreased to 1/n2 . Thismeans that the numerical aperture ofa dry objective and an immersion ob-jective differs by the factor n2, pro-vided the objectives can absorb raysof the same angular aperture. Thestandard numerical apertures of im-mersion objectives are 1.25 (waterimmersion), 1.30 glycerin immersion)and 1.40 (oil or homogeneous im-mersion). The values correspond tohalf the angular apertures � = 56°,59° and 68°; for dry objectives, thenumerical apertures would be re-duced to 0.83, 0.86 and 0.93.

Another advantage of immersionobjectives over dry objectives is theirconsiderable reduction or even entireelimination of interfering reflectedlight produced at the front surfacesof the coverslip and the front lens ofthe objective.

For the sake of completeness, wewould also like to mention the im-mersion technique used to determinethe refractive index of isolated solidbodies. The object to be measured is


ful Magnification

Lens diameter d

a b

2� 2’

2�’2

2� 2�’

4

Fig. 4:The resolving power of themicroscope (according toR.W. Pohl, 1941)2∆y object, 2∆y’ image,2� angular aperture on the object side,2�’ angular aperture on the image side,2 resolvable angle size on the object side,2’ resolvable angle size on the image side.

Fig. 5:Influence of the immersionmedium on the numericalaperture of the objective.2� = Angular aperture

of the objective(numerical aperture= n2 • y sin �)

1 = Limit angle oftotal reflection (= arcsin [n2/n1] � 41°) reached;grazing light exit.

2 = Total reflection

nBR · sin �’= d2b

2∆ymin = 2∆y’ nBR · sin �’nOR · sin �

2∆ymin = 1.22 · b · � · d

2 · b · d · nOR · sin �

2∆ymin = 0.61 · �

nOR · sin �

nOR · sin � =2∆y’

= const.nBR · sin �’ 2∆y


Useful magnification

To enable the human eye to see twoimage points separately, an angulardistance 2 of between 2 and 4 arcminutes, or

(7)

5.8 · 10-4 ≤ 2 ≤ 11.6 · 10-4

must exist between these points,according to Ernst Abbe. If the lowerlimit of the overall magnification ofthe microscope is Vu and the upperlimit Vo, where the overall magnifica-tion of the microscope VM equals thequotient of the apparent visual rangeof 250 mm and the overall focallength of the microscope fM, the cal-culation of Vu and Vo is easy:

(8a)

(8b)

with � = 550 nm = 5.5 · 10-4 mm

and

finally result in

embedded in an immersion liquid,the refractive index of which approxi-mates that of the object. Using aheating and cooling stage, the tem-perature is then varied until the re-fractive index of the liquid is identicalto that of the object. The fact – de-rived from the Dulong-Petit law –that the temperature dependence ofthe refractive index of solids is signifi-cantly lower than that of liquids isvery important here. The refractiveindex can be determined using eitherthe “Becke line” or, if high accuraciesare required, by interferometric means;please see the relevant literature.


(9a)

and

(9b)

or

(9c)

Vu ≈ 500 nAObj

and

(9d)

Vo ≈ 1000 nAObj

Therefore, the performance of themicroscope is meaningfully utilizedonly if the selected total magnifica-tion is no less than 500x and nomore than 1000x the numerical aper-ture of the objective

Our forefathers rightfully termedmagnifications > 1000 nAObj as“empty magnifications” because stillsmaller object details can no longerbe expected to be resolved, whichwill result in ineffective over-magnifi-cation.

Vu · 5.5 · 10-4 [mm]

= 5.8 · 10-4500 · nAObj

2∆y=

2∆y [mm] Vu = 5.8 · 10-4 (= 2’)fM 250

2∆y=

2∆y [mm] Vo = 11.6 · 10-4 (= 4’)fM 250

Vo · 5.5 · 10-4 [mm]

= 11.6 · 10-4500 · nAObj

2∆ymin = �

=�

2 sin � 2 nAObjRainer Danz, Carl Zeiss AG, Göttingen [email protected]

2) Due to the matchingrefractive indices of thefront lens, the immer-sion liquid and thecover slip, the micro-scopist first tends not to make any differencebetween coverslip-corrected (e. g. HI100x/1,40 ∞/0.17) and non-corrected (e. g. HI 100x/1.40 ∞/0)immersion objectives.This is certainly possiblein monochromatic light(centroid wavelength);in polychromatic light,however, immersionliquid and coverslipusually display differentdispersions, i. e. therefractive indicesdepend on thewavelength to a greater or less extent.This effect becomesapparent in themicroscope image withchromatic and sphericalaberration. Therefore:always carefully notethe correction state ofthe objective!


Front lens of the objective

Dry objective Oil immersion objective

Front lens of the objective

Air Immersion oil

Cover slip

Objectivewith smallangularaperture

Object plane

2�

Objectivewith largeangularaperture

2�

The resolving power of anobjective is the ability toshow two object detailsseparately from each other in the microscope image. The numerical aperture of theobjective directly determinesthe resolving power: thehigher the numerical aper-ture, the better the resolvingpower.

The theoretically possibleresolution in light microscopyis approx. 0.20 µm. Theresolving power of an objec-tive is defined by the formula

d: distance between twoimage points

�: wavelength of lightA: numerical aperture of

the objective

Resolving power

Refractive indexof various media

Refractive index n of the mediathrough which the light raypasses in the beam path of a microscope.

Air n = 1.000Glass n = 1.513Oil n = 1.516

d = �

2 x A

details

objective). The formula for the nu-merical aperture shows that, in addi-tion to the angular aperture of theobjective, the refractive index of themedium between the coverslip andthe objective is also used for thecomputation.

In the case of dry objectives, thelight rays are refracted away from theperpendicular on entering the air be-tween the coverslip and the objectivein accordance with the refractionlaw. Therefore, strongly inclined lightrays no longer reach the objectiveand do not contribute to the resolu-tion. With oil immersion objectives,immersion oil is inserted between thecoverslip and the objective: evenstrongly inclined light rays reach theobjective.

Numerical Aperture

The numerical aperture indicates theresolving power of an objective. Putmore simply, the resolving power ofan objective depends on how muchlight of a specimen structure reachesthe objective. This amount of lightdepends on what is called the angu-lar aperture of the objective. Thelarger the angular aperture, the bet-ter an objective will resolve the de-tails of a specimen. However, it is notthe angular aperture which is speci-fied on the objective, but the numeri-cal aperture.

The numerical aperture is definedby the formula A = n * sin � (A: nu-merical aperture, n: refractive indexof the medium between the coverslipand the front lens of the objective,sin �: half the aperture angle of the



this problem during Brewster’s time.Because microscope slides were veryexpensive at the time, microscopistsin the 19th century did not yet acceptoil immersion. Amici gave up on oilimmersion and converted to waterimmersion. A short time later in1853, he built the first water immer-sion objective and presented it inParis in 1855.

In 1858, Robert Tolles (1822-1883) built his first water immersionobjective which had two exchange-able front lenses: one for workingunder dry conditions, the other forwater immersion.

Approximately 15 years later in1873, he constructed his famous1/10 objective for homogenous im-mersion. Edmund Hartnack (1826-1891), who in 1859 presented hisfirst water immersion objective, alsoadded a correction ring for the firsttime. Hartnack sold around 400models over the next five years. By1860, many German microscopemanufacturers offered water immer-

Highlights from the History of Immersion

details

In the beginning, natural cedaroil was used. Gradual thicken-ing leads to alteration of therefractive index over time.Exposed to air, it turns to resinand becomes solid.Nowadays, synthetic immersionoil with a constant refractiveindex is used. It does not hardenin air and can therefore bestored longer.

Immersion oil


Robert Hooke (1635-1703) was thefirst to discuss the technique ofimmersion: “that if you would have amicroscope with one single refrac-tion, and consequently capable ofthe greatest clearness and brightness,spread a little of the fluid to be ex-amined on a glass plate, bring thisunder one of the globules, and thenmove it gently upward till the fluidtouches and adheres to the globule.”His “Lectures and Collections” from1678, published in his book “Micro-scopium” in the same year, thusmarked the beginning of oil immer-sion objectives.

Sir David Brewster (1781-1868)proposed the immersion of the ob-jective in 1812. Around 1840, Gio-vanni Battista Amici (1786-1868) pro-duced the first immersion objectivesthat were used with anis oil and hadthe same refractive index as glass.However, this type of immersion wasnot yet used to increase the aperture,but more to correct chromatic aber-ration. Amici had already recognized

INNO_07_Oelimmersion_E.qxd 15.08.2005 9:25 Uhr Seite 16

sion lenses, including Bruno Hasert inEisenach, Kellner in Wetzlar, G&SMerz in Munich and Hugo Schroderin Hamburg. Hartnack’s immersionlenses, however, were considered thebest.

At the “Exposition Universelle” in1867 in Paris, Ernst Grundlach (1834-1908) presented his new glycerin im-mersion lens, claiming that he devel-oped the lens because he wanted touse an immersion medium with ahigher refractive index than water.

In 1871, Tolles once again pre-sented something new: he usedCanada balsam as an immersionmedium for homogenous immersion.His discovery that Canada balsam hasthe same refractive index as thecrown glass that was standard at the time remained unused until ErnstAbbe discovered a suitable liquid in1877. The Zeiss Optical Works in Je-na also produced initial water immer-sion objectives in 1871. In 1872, CarlZeiss introduced the Abbe water im-mersion objective. Three objectives

were offered in the Zeiss catalog atthe time, all with an aperture of180°. They had different working dis-tances, but also a numerical apertureof 1.0. Objective no. 3 was equippedwith a correction ring.

In August 1873, Robert Tolles builta three-lens objective for homoge-nous immersion in balsam with a nu-merical aperture of 1.25. It was thefirst homogenous immersion systemfor microscopes to be recognized atthe time. In the same month, he pro-duced his first objective for glycerinimmersion with a numerical apertureof 1.27.

In August 1877, Carl Zeiss beganbuilding Abbe’s oil immersion objec-tives which later became known as“homogenous” immersion. The de-sign of the Zeiss oil immersion objec-tives was influenced by the work of J. W. Stephenson, which Abbe em-phasized in a lecture to the Jena Soci-ety for Medicine and Natural Sciencein 1879.

In 1879, Ernst Abbe published his

“On New Methods for ImprovingSpherical Correction” in the “RoyalMicroscopical Society” magazine. Inthis article, Abbe described the opticshe used in his 1873 experiments. Healso added that homogenous immer-sion systems make it possible toachieve an aperture at the limits ofthe optical materials used and avail-able at the time. Robert Koch wasone of the first to utilize the Abbe oilimmersion objective and the Abbecondenser system for research pur-poses. In 1904, Carl Zeiss manu-factured its 10,000th objective forhomogenous oil immersion.

Objectives

1,2,3 propanetriol – is the mostsimple tertiary alcohol. The Greekword glykerós means “sweet”. The viscous, hygroscopic, sweet-tasting liquid boils at 290 °C andfreezes at 18 °C. Glycerin can bemixed with water and lower-orderalcohols. A mixture of water andglycerin is used in microscopy forimmersion. It is mainly used in UVmicroscopy as glycerin transmitsUV light.

Glycerin

details


INNO_07_Oelimmersion_E.qxd 15.08.2005 9:25 Uhr Seite 17


The history of microscopy startedaround 1590 with Dutch spectaclemakers. The first “simple” micro-scopes date back to Antony vonLeeuwenhoek (1632-1723) and his contemporaries. Leeuwenhoekbuilt microscopes with a single,small lens displaying magnifica-tions of up to 270x. This enabledhim to discover protozoa (single-celled organisms) as early as1683. The “combined” micro-scopes are attributed to the Eng-lishman Robert Hooke (1635-1703), who is known to haveused these for the first time.“Combined” microscopes consistof an objective lens and an eye-piece. Hooke already recognizedthe importance of microscope illu-mination at that time. However,the aberrations of both micro-scope types impaired preciseobservation. Nevertheless, theyformed the base of the pioneer-ing microscopic discoveries in the19th and 20th centuries.

Abbe’s key theoryon microscope imageformation

In the end, it was Carl Zeiss who rec-ognized the importance of a solidtheoretical basis and who initiatedand also financed Abbe’s research.The major breakthrough for thebuilding of microscopes came withthe theory of microscope imageformation from Ernst Abbe (1840-1905). After countless calculationsand experiments, Abbe realized thatit is the diffraction image in the back focal plane of the objective that is decisive for image formation.In 1873, he wrote: “No microscopepermits components (or the featuresof an existing structure) to be seenseparately if these are so close toeach other that even the first lightbundle created by diffraction can no longer enter the objective simul-taneously with the non-diffractedlight cone.”

From the History of Microscopy: Abbe’s

18

Until 1866 – the year when the co-operation between Carl Zeiss andErnst Abbe began – microscopes, andthe microscope objectives in particu-lar, were made by trial and error,resulting not only in some micro-scopes with outstanding optical per-formance, but also in some with lessdesirable features. Carl Zeiss (1816-1905) and Ernst Abbe were awarethat optimum and – above all –consistent performance would onlybe possible on a sound theoreticalbasis. The first calculations weremade of the geometric beam path.To improve correction, Abbe usedlower apertures than those of theobjectives made by Zeiss until then.The results were not really satisfacto-ry: fine specimen structures remainedblurred, and their resolution was lessgood than that obtained with the old objectives with a wider angularaperture.

INNO_09_diffraktion_E.qxd 15.08.2005 9:27 Uhr Seite 18

This is also the core of Abbe’s theoryof microscope image formation. Histheory, based on the wave charac-teristics of light, shows that themaximum resolution is determined by half the wavelength of the lightused, divided by half the numericalaperture.

Abbe’s theory of image formationand resolution limits was rejected bymany biologists and mainly by micro-scopists in England, who were toobiased by the old microscopy tech-nique of using strongly magnifyingeyepieces, a method known as emptymagnification.

Finally, Abbe was able to prove histheory with a system of experimentshe first demonstrated using the ZEISSMicroscope VII. Robert Koch usedthe same Microscope VII for his dis-covery of the tuberculosis bacterium.


Diffraction Trials

Microscope stand VII. Microscope stand I.

Cover page of brochure onthe diffraction apparatus.

Abbe’s illumination apparatus.



3

4

1

2

5

6

7

Diffraction experiments

Even today, diffraction experimentsstill play a major role in trainingcourses in microscopy, and make amajor contribution to the under-standing of modern microscopytechniques. Abbe created almost 60experiments to prove his theory ofimage formation. A diffraction platewith various objects engraved in theform of lines and dots is used as aspecimen. The condenser is removedso that the light source lies at infinityand can be made to adopt a point-shaped structure by closing the lumi-nous-field diaphragm (Fig. 1). Re-moval of the eyepiece or the use of an auxiliary microscope permitsviewing of the images produced inthe back focal plane of the objective.


is twice as distant from the 0thmaximum as in the 16 µm grid.

Point grid

In the diffraction image of the pointgrid (Fig. 8), the respective primarydiffraction spectrum (Fig. 9) can beseen in the back focal plane of theobjective. From this, Abbe concludedthat each specimen forms a specificdiffraction image of the light source.

Influencing thediffraction image

If an intermediate component with aslit is inserted between the objectiveand the nosepiece (Fig. 10), in whichvarious stops can be inserted, partsof the diffraction image can be faded out. For more precise orienta-tion, the intermediate componentcan be rotated through 360 degrees.This means that the primary diffrac-tion image is changed by artificialmeans.


Single slit

With a single slit (Fig. 2), a light strip(Fig. 3) appears in the back focalplane of the objective, which is per-pendicular to the optical axis anddisplays the point-shaped light sourcein the center. This light strip is pro-duced by the diffracted light wavesat the edges of the slit.

Double slit

The double slit (Fig. 2) enables obser-vation of the interference phenome-non: the image of the light source islocated in the center, while brightand dark sections extend to the rightand left in a regular sequence (Fig.4). The bright sections display charac-teristic color fringes (spectral colors).Abbe designated this image in theback focal plane of the objective asthe diffraction spectrum.

8

9 10

Line grid with16 µm gratingconstant

In the produced diffraction image ofthe 16 µm line grid (Fig. 5), the im-age of the light source, also calledthe zeroth maximum, and the firstand second order secondary maximaare clearly separated from each otherand imaged much more sharply (Fig.6) than is the case in Fig. 4. Further-more, it is also evident that blue lightis less diffracted than red light.

Line grid with 8 µm gratingconstant

In the diffraction image of the 16 µmline grid (Fig. 5), the 1st secondarymaximum is twice as distant from the0th maximum, and the 2nd secondarymaximum is no longer visible at all(Fig. 7). From this, Abbe concludedthat the closer the structures – orlines in this case – the more the lightwaves are diffracted, explaining whythe 1st maximum in the 8 µm grid

Fig. 10:Abbe’s diffraction apparatus b.



Point grid

From the diffraction image of thepoint grid (Fig. 9), the 0th and thefirst secondary maxima in the hori-zontal axis are faded out via the slit.In the intermediate image, a line gridthen appears in the perpendiculardirection (Fig. 11), and at an angle of45° when the slit is oriented diago-nally (Fig. 12). A particularly remark-able feature of the artificially pro-duced 45° grating is that the lines arecloser to each other than in other im-ages. This is bound to be the case be-cause the secondary maxima in the45° diffraction image are furtheraway from the 0th maximum than inthe perpendicular or horizontal dif-fraction images.

With these experiments, Abbe fi-nally showed that the image in themicroscope is created in the spacebetween the primary diffraction im-age (back focal plane of the objec-tive) and the intermediate imageplane through interference of dif-fracted light waves.

In a further experiment, Abbedemonstrated why the resolutionformula is

numerical aperture.

Abbe pushed the point-shaped lightsource to the edge (known asoblique illumination): therefore, the1st secondary maximum can be twiceas distant as in straight illumination,i. e. the distance d between twopoints or lines can be twice as small.On this basis, Abbe had already de-veloped the illumination apparatuswith focusing condenser in 1872 (Fig.14). In today’s microscopy, we use uni-lateral oblique illumination to achievefull resolution with the maximumcondenser aperture.

The theory of microscope imageformation and its practical implemen-tation defined the resolution limitsand thus enabled the scientific con-struction of microscopes. Abbe could

then concentrate on the correction ofspherical and chromatic aberration.He realized that this requires thedevelopment of special glass materi-als. His collaboration with the glassmaker Otto Schott (1851-1935) start-ed in 1879, and the first Apochromatobjectives featuring high color fidelitywere already launched in 1886.

In 1893, August Köhler (1866-1948) developed his illuminationtechnique with separate control ofluminous-field diaphragm and con-denser aperture on the basis ofAbbe’s results. Köhler also developedthe microscope with ultraviolet light,which was primarily built to increasethe resolution by a factor of 2 relativeto green light. Finally, the phasecontrast technique from the Dutchphysicist Frits Zernike also is attribut-able to manipulation in the backfocal plane of the objective.

With his theory and experiments,Ernst Abbe decisively shaped the de-velopment of microscopy in the 19thand 20th centuries. Numerous Nobelprizes are directly or indirectly con-

11 12

d = �

2nx sin �2 x n x sin � =

14


Image plane

Back focal plane

Specimen plane

Image of the specimen

Diffraction image of the specimen

Specimen13


nected with microscopy. Abbe him-self was twice nominated for theNobel prize. Pioneering examinationsin cell and molecular biology wouldnot have been possible withoutmodern light microscopy. Metallogra-phy would probably not haveachieved its current status withoutmicroscopy, and semiconductor tech-nology would probably not even existat all.

Heinz Gundlach, Heidenheim



The importance of light is empha-sized in the First Book of Moses inthe Bible: “In the beginning, Godcreated the heaven and the earth.And the earth was without form,and void; and darkness was uponthe face of the deep. And theSpirit of God moved upon theface of the waters. And God said,Let there be light: and there waslight. And God saw the light, thatit was good: and God divided thelight from the darkness.” Withoutlight life is impossible. Light playsan important role in our lives.And the question of the “natureof light” is one that we havealways endeavored to answer.

Besides mechanics, optics wouldseem to be the oldest field in whichscientific work has been conducted.The Babylonians, on the basis of theirexperience, were already applyingthe law of the rectilinear propagationof light around 5000 BC in the use ofastronomical instruments.

There is evidence of scientificstudy in the field of optics in Greece

in the 6th century BC: here the em-phasis was on explaining the effectthe visible object had on the eye. Thevarious schools developed ideas thatdiffered from each other to a greateror lesser extent and were generallyrather imprecise.

The predominant theory in An-cient Greece was the extramissiontheory, which can presumably betraced back to Pythagoras (570/560-480 BC) and was later supported in particular by Euclid (around 300BC) and Ptolemaeus (around 100-160 AD). The extramission theoryassumed that we are able to see as a result of hot rays that emanatefrom our eyes towards an object. Theresistance these rays meet with whenthey reach the cold object causesthem to be sent back, enabling theinformation they have gathered toreach the eye. The ability of many an-imals to see at night was put forwardin support of this theory.

Aristotle (384-322 BC), in particu-lar, had a different view. He believedthat light is not something physicalthat moves between the object andthe eye, but rather that the processof seeing is the result of the effect

the object has on the eye by meansof the medium between them (“thetransparent”).

In addition to the process of see-ing in itself, the Greeks also studiedthe laws of geometric optics. It seemsthat Plato (424-347 BC) was awareof the law of reflection and he de-scribed the reflection of concave andcylindrical mirrors. The mention ofoars bending in water indicates thatthe phenomenon of refraction wasalso familiar. The playwright Aristo-phanes (445-385 BC) described theeffect of burning glasses (glass lensesor glass globes filled with water).Ptolemaeus, who summarized theentire optical knowledge of the an-cient world and systematically exam-ined the refraction of light, is perhapsthe most important optical scientistof that time.

During the Middle Ages, Chris-tianity was not particularly open toscience. It was the Arabs who notonly collected and translated the an-cient writings but also made theirown scientific contributions. Themost important Arab scientist wasAbu Ali Al-Hasan Ibn Al-Haitham(965-1040), also known as Alhazen,

The Science of Light

INNO_10_Licht_E.qxd 15.08.2005 9:30 Uhr Seite 24


In Huygens’ famous principle,every point on a forward-moving wavefront is seen as a source of new waves. He usedthis principle to develop thewave theory of light. With a new method (1655) for thegrinding and polishing of lens-es, Huygens achieved an im-provement in optical perform-ance. This enabled him to dis-cover the moon of Saturn andto make the first exact descrip-tion of the rings of Saturn. To observe the night sky, Huy-gens developed the pendulumclock with an exact time meas-ure. In 1656 he invented theHuygens telescope. He devel-oped theories about centrifugalforce in circular motion. Thesehelped the English physicist Sir Isaac Newton to formulatethe law of gravitation. In 1678 Huygens discovered thepolarization of light throughbirefringence in calcite.

who wrote more than 200 works onoptics, astronomy and mathematics.His principal work, the “Book of Op-tics”, contained descriptions and ex-planations regarding light and vision.

From the 12th century, the mainscientific focus shifted geographicallyfrom the East back to the West ofthe known world. Initially, however,only the works of Alhazen, Ptole-maeus and Euclid were translatedand summarized. There is evidencethat Roger Bacon (1214-1294), a Do-minican monk, studied the cameraobscura, which he recommended forobserving solar eclipses. Bacon alsopredicted the development of eye-glasses and the telescope. Eyeglasseswere apparently invented in Italy atthe end of the 13th century.

At first, however, it was notknown how they functioned exactly,since people did not know how theeye saw, nor how lenses worked.Giovanni Battista della Porta (1535-1615) compared the eye with a cam-era obscura. Father Franciscus Mau-rolycus (1494-1575) recognized thatdefective vision was caused by theincorrect curvature of the lens.

Johannes Kepler (1571-1630) is

regarded as the founder of modernoptics. He succeeded in correctly ex-plaining how the camera obscuraand the eye worked, including thelens and the retina. Thomas Harriott(1560-1621) was supposedly the firstperson to discover the law of refrac-tion.

In 1637, Rene Descartes (1596-1650) derived a theory relating to theLaw of Refraction in his work “LaDioptrique”. He was one of the firstto attempt to explain all optical lawsand phenomena on the basis of themechanical properties of the lightsource and the transparent medium.The work of Johannes Marcus Marcide Kronland (1595-1667) andFrancesco Maria Grimaldi (1618-1663) gradually brought us closer tothe wave theory of light, which wasthen supported emphatically byRobert Hooke (1635-1703). At thesame time as Hooke, the Jesuit priestIgnace Gaston Pardies championedthe theory of the wave nature oflight. Nevertheless, it is ChristiaanHuygens (1629-1695), with the Huy-gens’ principle that was named afterhim, who is regarded as the truefounder of the wave theory of light.

Christian Huygens (1629-1695)Dutch astronomer,mathematician, physicistand clockmaker.

Birefringent calcite.

INNO_10_Licht_E.qxd 15.08.2005 9:30 Uhr Seite 25


Since its inception, the zoologicalstation has been devoted to basicresearch in biology for all its in-ter-disciplinary activities – fromevolution and molecular biologyto ecophysiology. The station cel-ebrated its 125th anniversary in1998. Named after founder, finan-cier and first director, AntonDohrn, the center took 18 monthsto complete, finishing in Septem-ber 1873. Located in Naples, Italy,the station served as an examplefor many other marine biologicalcenters and institutes. Thisrenowned list includes WoodsHole in the USA and Misaki inJapan, as well as the Kaiser Wil-helm Institutes which later be-came the Max Planck Institutes. Anovelty when the station wasfounded, its internationality wasfostered and ensured by influen-tial scientists at the time, CharlesDarwin and Rudolf Virchow,among others.

wealth of life forms, particularly sim-ple forms, caused many scientists tosee the oceans as a source of biologi-cal models, experimental objects andas a metaphor for fundamental bio-logical problems such as the organi-zational plan of life, embryogenesis,general physiology, evolution andphylogeny.

Johannes Müller (1801-1858), con-sidered the founder of physiologyand theoretical biology, raised inter-est in marine organisms for the un-derstanding of fundamental biologi-cal problems. The concept of marinebiology research published by Müllerwas a means of explaining the funda-mental biological concept. The sta-tion’s first boat carried his name asan indication of its purpose. It wasused to gather marine plants andanimals.

First marine institutes

Zoologist and parasitologist P. M. vanBeneden from Leuven, Netherlandsfounded the first marine laboratory inOstende 1843. Similar initiatives inNorth America emphasized the needfor such research institutes: Louis

Stazione Zoologica Anton Dohrn, Naples,

26

Naturalists as well as philosophershave always shared a fascination forlife under the sea. This curiosity, sci-entific observation and legendspassed down through the years, ledPliny the Elder (23-79 A. D.) to penNaturalis Historia. It attracted atten-tion to sea life, an unending sourceof wondrous (Mirabilia) and fantasticmonsters, a place of mystery and a constant source of life and beauty.To the German science scene in the19th century, which was marked bymen such as Alexander von Hum-boldt, the ocean was a place of ele-mentary life forms and a symbol ofthe endless search for knowledge.

Marine life became the focus ofinterest of all those who recognizedthe philosophy of nature. Appearingin the “protoplasmic theory of life”,initial forms of cell theory looked for“elementary forms of matter”, the“primordial mud” teeming with one-celled organisms, in the depths of theoceans. The new generation of biolo-gists from the 1850s and 1860s waswell versed in “natural philosophy”and in Darwinism. They viewed theocean as a source of knowledge andas an experiment of life. In the sec-ond half of the 19th century, the

1

Fig. 1:Group of researchers at the Stazione Zoologica atthe end of the 19th century.

INNO_11_12_zoo_dohrn_E.qxd 15.08.2005 9:34 Uhr Seite 26

Agassiz founded the AndersonSchool of Natural History in 1873;Johns Hopkins University the Chesa-peake Zoological Laboratory in 1878.The Woods Hole Oceanographic In-stitution opened in 1892.

However, these were all universityand institute field stations. They canalso be split up into two categories:centers such as Naples were dedicat-ed to research and practical training,while French and American instituteswere used primarily for teaching.

Deciding on Naples

During his stay at the zoological cen-ter in Messina, Anton Dohrn realizedthat a permanent laboratory struc-ture was required to study ocean life.This is where his dream of a “fullhouse” for ocean research started:instant and permanent availability ofinstruments, laboratory stations, lab-oratory services, chemicals, booksand much more.

The diversity of life in the Gulf ofNaples, the size of the city and its in-ternational reputation contributed toDohrn’s decision to locate his centerin Naples. With a mixture of imagina-tion, willpower, diplomatic skill, luckand some friendly help from otherscientists, artists and musicians, hewas able to remove any doubts, un-certainties and misunderstandings,and convince the city to donate apiece of land directly beside the sea:a piece of land at one of the mostbeautiful places in Naples – Park VilleReale. He promised to finance the zoological center himself. Dohrnknew exactly what he wanted. Thecornerstone was laid in March 1872and construction of the station wascompleted in September 1873. Heand his father paid for two-thirds ofthe construction costs. The remainderwas financed by loans from friends.Although the center had just openedits doors, the first scientists headedto Naples in September 1873. The of-ficial inauguration was on April 14,

1875 and Anton Dohrn signed thecontract with the City of Naples.

Anton Dohrn’s idea of independence

In order to increase the international-ity of the center, and to ensure theeconomic – and therefore political –independence and freedom of re-search, Anton Dohrn introduced aseries of innovative measures tofinance projects. The system forrenting work and research spacedeserves to be mentioned first. Foran annual fee, partners such as uni-versities, governments, private insti-tutions, and even individuals werepermitted to send a scientist toNaples for one year. Everything need-ed for unlimited research was avail-able. Scientists could even use theknowledge of station employees.Everyone was free to pursue theirprojects and ideas. The fast and freeexchange of ideas, methods, tech-niques and instruments, as well asthe contact between scientists fromdifferent cultures, was decisive forthe success of the system. In 1890,for example, 15 countries rented 36tables for one year. More than 2,200scientists from Europe and Americahad worked at the center by the timeof Dohrn’s death in 1909.

Internationality increased as a re-sult of scientific publications. Theseincluded Notes from the ZoologicalStation in Naples (1879-1915), whichlater became the Pubblicazioni dellaStazione Zoologica di Napoli (1924-1978) and has appeared as MarineEcology since 1980. The ZoologicalAnnual Report (1880-1915) also ap-peared for a short time. The Faunaand Flora of the Gulf of Naplesmonograph is still considered anoutstanding work today.


Italy

Gaius Plinius Secundus, betterknown as Pliny the Elder(Latin: Plinius maior), anancient author and scientist, is best known for his scientificwork Naturalis Historia. Hewas born around 23 A. D. inNovum Comum and died onAugust 24, 79, in Stabiae. TheNaturalis Historia (occasionallyHistoria Naturalis) comprises a comprehensive encyclopediaof natural sciences and re-search. It is the oldest knowncomplete systematic encyclo-pedia. The Naturalis Historiaconsists of 37 books with atotal of 2,493 chapters. Thebibliography cites almost 500authors, including 100 primaryand almost 400 secondarysources.

The station’stechnical setup

The station has always provided sci-entists with state-of-the-art researchequipment which was acquired eitheras a gift or at a very low price. Thelatest developments from Carl Zeisswere used, tested and presented tothe guest scientists. Ernst Abbe, oneof Anton Dohrn’s few close friendsmade it possible for the station topurchase Zeiss microscopes and otheroptical instruments at cut-rate prices.Station employees not only assistedin the optimization of the instru-ments, but also aided in distributionto the international science commu-nity. Employees and guest scientistsconstantly improved the scientificmethods, techniques and instrumentsprovided to the station.



Well-known visitors

The zoological station has never hadits own research project. The struc-ture of the center always reflectedthe interests of its guests. Accordingto statements by Theodor Boveri,Dohrn always had an eye open forthe importance of the different scien-tific aspects and their interaction inthe overall scheme of things. Thiswas the only way to attract the bestscientists of the time to Naples.

Nobel Prize winner Fridtjof Nansenwas accepted by Dohrn in 1886 al-though he did not have a financialagreement with Norway. Nansen“found” a new field of interest: hotly

debated by physiologists and histolo-gists at the time, the relationship be-tween ganglion cells and nervefibers, the nature of nerve impulsesand brain functions at a cellular levellater became a traditional field of in-terest. A visit by Robert Koch toNaples in 1887 convinced Dohrn ofthe necessity of establishing a bacte-riological laboratory. Developmentalbiology examinations on sea urchinswere first conducted by TheodorBoveri in 1889 and later by OttoWarburg.

Art and culture in a scientific facility

The significance of the zoologicalstation extends far beyond pure sci-entific aspects. It is also known forits humanitarian values and its cul-tural climate. For the majority of themany guest scientists, the “Naplesexperiment” was an impressive mix-ture of new research, human experi-ence, acquiring new methods andthe exchange of ideas and culturaldifferences. The zoological station isthe only institution in the worldwhere science, art and music wereintegral elements of a unique proj-ect, the complementary halves of adream, from the beginning. The ar-chitectural design and the technical-scientific equipment are a perfectmatch. Art and music were an essen-tial element of cultural life in the19th century. Dohrn wrote to E. BWilson in 1900: “Phylogeny is a sub-tle thing. It requires not only the an-alytical powers of the researcher, butalso the constructive imagination ofthe artist. Both must balance eachother out, otherwise it does not suc-ceed.”

The Stazione Zoologica organism

To this day, many complementaryfacts contribute to the uniqueness ofthe station: the high level of scientificactivity, the active and constant ex-change of information with the inter-national scientific community, theflexible organizational structure andthe associated independence ofpolitical and academic institutions,the incomparable library, the avail-ability of state-of-the-art instruments,the cultural atmosphere and thecreative dialogue between differentcultures. Tradition and innovationhave merged right from the begin-ning of the station and enabled theStazione Zoologica “organism” tosurvive until now. The zoologicalstation has been officially called“Stazione Zoologica Anton Dohrn”since 1982 and has almost 300employees.

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Fig. 2:Delivery note/invoicefor Microscope Stand IVa

No. 29057 from April 20,1898.

Fig. 3:Theodor Boveri (1862-1915):the development of doubly(di-sperm) fertilized seaurchin eggs.

www.szn.it



Anton Dohrn founded the zoo-logical station in Naples in 1870.For decades it was the leadinginternational center for marineresearch.

Anton Dohrn was a zoologist andone of the first outstanding resear-chers of phylogeny. He came from awell-to-do family in the German cityof Stettin. In his early childhood, helearned that art and science coexistand interact: his father Carl August(1806-1892) corresponded with ar-tists, poets and scientists such asAlexander von Humboldt and FelixMendelsohn. His children were requi-red to “know their Goethe”, beknowledgeable about music andshare his passion for science.

Dohrn studied in Königsberg, Bonnand Jena under Rudolf Virchow, ErnstHaeckel and Carl Gegenbaur. Follo-wing his studies in medicine and zoo-logy, he became interested in thetheories of Darwin. In 1870, he foun-ded the zoological station for theresearch of marine fauna in Naples,Italy, one of the first marine researchcenters. He also studied the phyloge-ny of arthropods based on embryolo-gical and comparable anatomical da-ta. Building on his insights, he wasthe first to suggest that vertebratesevolved from annelids. Furthermore,he described the “principle of thechange of functions”.

Dohrn earned his doctorate in1865 in Breslau. He qualified as alecturer in 1868 in Jena and taughtzoology until 1870. From 1874 untilhis death, he was director of the ma-rine research station in Naples, Italy(Stazione Zoologica di Napoli). In1874 he married 16 year old Mariede Baranowska.

Despite his nationality and culturalorigins, Anton Dohrn received con-siderable support from the Britishnatural science tradition during therealization of his dream of foundinga marine biology laboratory. At theannual meeting of the British societyin 1870 in Liverpool, a committeewas founded with the intention ofpromoting the foundation of zoologi-cal stations in different regions of theworld. In fact, it was this committeethat increased the fame of Dohrn’szoological station in Naples in the En-glish-speaking world with regularlypublished reports and articles in Na-ture.

Felix Anton Dohrn

“…not only that Abbe provid-ed new instruments at a very low price, or evendonated them, he also re-ceived suggestions from there,the control of the practice,the critical thoughts of experi-ence. The station was also a place where foreign re-searchers were introduced toand acquired Zeiss equipment,and then announced thesplendor of superior Germanworkmanship in their homecountries. The station wasalmost a type of ideal exportwarehouse and Dohrn wasdelighted to write to Abbethat Balfour acquired thisapparatus and he wants onefor everyone…”

Theodor Heuss was friendswith Dohrn’s son Boguslavwho, on the 100th birthday ofthe great natural scientist in1940, requested that Heusswrite a comprehensivesummary of the life work of Anton Dohrn.

From “Anton Dohrn: A Life for Science” by Theodor Heuss (1940)

Felix Anton Dohrn

Born December 29, 1840,in Stettin,Died September 26, 1909,in Munich

Anton Dohrn, 1898,drawing byJohannes Martini.



An unexpected treasure is hiddenabove the aquarium and betweenthe labs, technical equipment andoffices at the Zoological Stationin Naples: the Hall of Frescos, aroom Anton Dohrn dedicated tomusic and entertainment.

his meeting with friends of AntonDohrn, with the world of the an-tiques and the sunny life on theMediterranean.

Hilderbrand studied in Nuremburgand Munich. In 1867 he accompa-nied his teacher, von Zumbusch, toRome. From 1872 to 1897, he livedin Florence and focused his work onthe sculpture of the Italian Renais-sance. With his marked tectonictalent, he created fountains andmonuments.

The Hall of Frescoes

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Two German artists, Hans vonMarées, and sculptor and architectAdolf von Hildebrand, decorated itwith a fresco cycle that plays aunique role in the history of 19thcentury art.

Hans von Marées (1837-1887)was one of the most influential Ger-man artists in the second half of the19th century. He developed an ideal-istic style of painting with clarity ofform focused on people. As a painterhe was attracted to the world of theantiques. As an art theoretician, heworked together with Adolf vonHildebrand (1847-1921), the leadingsculptor of his time, on the theory ofpure visibility.

Following his studies and trainingin Berlin (1853-1855) and Munich(from 1857), and travels to Italy,Spain and France (1864-1866),Marées completed the frescoes inNaples which represent a high pointof his work. They are the result of

Fig. 1:View of the hall of frescoesat the Stazione ZoologicaAnton Dohrn.

Fig. 2:Desk in front of the east wall of the hall of frescoes with the “La Pergola” fresco.

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Christiane Groeben, [email protected]

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During his trip to Italy in 1786,Johann Wolfgang von Goethealso made a stop in Naples:“Everyone is on the street, sittingin the sun, as long as it shines.The Neapolitans believe they areliving in paradise,” he wrote inFebruary 1787.

Naples is well known, beloved andpopular and attracts many visitors. Itis a city with its own character, a cityof enchantment, entrapping every-one in its spell with the beauty of thesea, the magic of history, the extra-ordinary architecture and its friendlypeople.

The city was founded sometime inthe 8th century B. C., most likely byinhabitants of the Greek Cumaecolony. In the 17th century, Naplesboasted 300,000 citizens, making itthe second largest European cityafter London. Today, Naples (Greek:nea polis: New City, Italian: Napoli) isthe third largest city in Italy afterRome and Milan, and is the largestcity in southern Italy. It is the capitalof the Campania region. The city cur-rently has approximately one millioninhabitants; together with the sub-

urbs around three million. It is situat-ed halfway between Mount Vesuviusand another volcanic region, theCampi Flegrei (Phlegraean Fields) onthe Gulf of Naples.

Science quickly found a home inthe city: in 1224, Friedrich II von Ho-henstaufen founded the University ofNaples. For some, it is the loudest,most polluted and chaotic city; forothers it is the most beautiful andlively. Five and six story apartmentbuildings existed as early as the 16th

century. It was the largest city in Eu-rope and space was at a premium.Scholars came to the city at all timesto revel in its artistic splendor.

Naples is considered the birthplaceof pizza. The recipe for a margheritahas remained unchanged since the16th century: topped with onlytomato sauce, mozzarella and basil,the pizzaiolo places the culinarydelight into the wood-burning brickoven. Three minutes later, it is readyto eat and the next one takes itsplace.


Fig. 1:Menu from 1907 with the Stazione Zoologica.

Fig. 2:The Stazione Zoologicaaround 1873.

Bella Napoli

“See Naples and die,” is anexpression often used whensomeone is completely mesmer-ized by the beauty of somethingthey have seen.It is based on the Italian saying“Vedi Napoli e poi muori”. In Italian it has a funny doublemeaning. It is a play on wordswith the name of a city,“Muori”, that is located justbeyond Naples which can onlybe seen upon leaving, and theverb form “muori”, meaning todie. Enjoying a favorable climate,Naples is a special place: theItalians consider it a piece ofheaven on earth, while theGermans and French saw it asthe center of sorcery and blackmagic until the 19th century.

See Naples and die

details

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Specimen:Prof. M. Bastmeyer,Dr. M. Marx, FriedrichSchiller UniversityJena, Germany.

Photo:Dr. M. Zölffel, Carl Zeiss.

The zebra fish (danio rerio) is very easy to breed, requiring onlythree days to develop from anegg into a free-swimming larva.As the zebra fish remains trans-parent throughout its entire de-velopmental period, it is an idealorganism for examinations of ver-tebrate organ development underthe microscope. Examinations onzebra fish models lead to a betterunderstanding of organ develop-ment of “man the vertebrate”and his diseases.

Fig. 1:3-day-old zebra fish in red and greenfluorescence: antibodylabeled axon populationsand GFP motor neuronsNeoLumar S 1.5x150x magnification.

For retinal diseases

Degenerative changes to the retinaare genetic diseases in people thatcause photosensitive receptor cellsto die. This is one of the most com-mon causes of blindness in humans.Zebra fish suffer from similar geneticeye diseases. The development ofthe fish eye and the activation of thenerve fibers in the zebra fish’s eyeare very similar to the human eye.The short development period of the zebra fish permits observation ofthese degenerative retinal processeswith the SteREO Discovery.V12 andLumar.V12 high-resolution stereo-microscopes as if in slow motion,thus enabling better research intothe cause of blindness and possibletreatment methods. The eyesight ofzebra fish larva is examined using aspecial test. The stereomicroscopemakes it possible to examine thedeveloping eyes of blind as well as normally sighted fish and alsocompare them to each other.

The First Stereo-microscope Came from Jena

It all started at the Weimar Courtyardin Jena in 1892. Under the leadershipof Ernst Abbe and developmentalbiologist Ernst Haeckel, this was the regular meeting point for science employees from the universi-ty and the Zeiss Works. At one of these gatherings, American zoologistHoratio S. Greenough expressed hiswish for a ”binocular microscopethat renders true 3D images.”

Carl Zeiss set to work on fulfillingthis wish and constructed the firstindustrially manufactured stereo-microscope at the end of 1897 – theGreenough double microscope.

The Zebra Fish as a Model Organism for

From Users

In cancer research

The zebra fish has already replacedthe well-established model organism– the mouse – in cancer research: themouse has a longer developmentalcycle and the ontogenesis stages are less translucent than in the zebra fish. Until now, mice were usedthat develop cancer cells (e. g.leukemia) caused by genetic muta-tions. These cells are transfected with GFP using molecular biologytechniques. The extremely powerfulSteREO Lumar.V12 fluorescencestereo microscope enables scientiststo optimally view and research theprogression of the disease.

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r Developmental Biology

It had two tubes tilted towards eachother at a convergence angle of 14degrees with objective lenses at thelower ends. Carl Zeiss ensured thatthe axes on the two lenses were inone plane, i.e. they actually intersect-ed. Porro erecting prisms were usedbetween the lenses and the eye-pieces. These prisms ensure that im-ages are upright and unreversed, i. e.the images can be viewed as they are in reality. This was also a demandfrom Greenough and the guaranteeof a true orthoscopic impressionwhen looking through the stereo-microscope, or dissecting microscopeas it was called back then.

The invention of the stereomicro-scope at Carl Zeiss was an essentialcontribution to the rapid upswing inthe still young developmental and

marine biology: the Greenough stere-omicroscope enabled exact researchinto the lifecycle of many inverte-brates (e. g. polyps, bristle worms,snails) for the first time. It also con-tributed considerably to the most im-portant discoveries in developmentalbiology and genetics of the early 20th

century (Wilhelm Roux, Hans Spe-mann, Thomas Hunt Morgan).

Today, the SteREO Lumar. V12 issetting new standards for the fluores-cence microscope examination ofcomplex issues related to develop-mental genetics in biological andclinical research.

Fig. 2:Sketch of Greenough’sidea for a binocularmicroscope that renderstrue 3D images.

Fig. 3:The Greenough double microscope from Carl Zeiss.

Fig. 4:Dissecting microscopefollowing the design of Paul Mayer.

Fig. 5:SteREO Lumar.V12.

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www.zeiss.de/micro

INNO_15_Zebrafisch_E.qxd 15.08.2005 9:56 Uhr Seite 33


The new high-tech microscopeprocedure, SPIM (Selective PlaneIllumination Microscopy), permitsfascinating insights into living or-ganisms and makes it possible toobserve processes – even those indeep-lying tissue layers. The newdevelopment has its roots in thetheta microscope from the 1990swhich was designed for examina-tions of large specimens withhigh 3D resolution. The funda-mental light microscopy principleis fluorescence detection at an an-gle of 90° relative to the illumina-tion axis. SPIM now unites thetechnology of the targeted illumi-nated plane in the specimen withthe theta principle, thus permit-ting optical cutting.

SPIM – A New Microscope Procedure

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In the SPIM procedure, the specimenis no longer positioned on the micro-scope slide as usual, but in a liquid-filled specimen chamber which al-lows it to remain viable during themeasurement. Rotating the specimenchanges the illumination and detec-tion axes relative to the specimen,permitting better detection of previ-ously hidden or covered areas. Com-plex development processes such asformation of the eyes and brains offish embryos or other specimens canbe observed and documented.

INNO_22_SPIM_E.qxd 15.08.2005 10:33 Uhr Seite 34


Fig. 1:Medaka fish.

Fig. 2:Pictures of Medaka fishembryos, head region,different perspectives.The last (or fifth) picture in a series shows the fusionof the data sets.

Fig. 3:3D display of the pictureseries from Fig. 2.Display in various exposureangles. The center imageshows a section through thefusion of the data set.

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Jan Huisken,European MolecularBiology Laboratory (EMBL).

Ernst Stelzer (front) and Jim Swoger, European MolecularBiology Laboratory (EMBL).

180° 90°

270° 0°

Fusion



In the SPIM method, which is basedon the theta principle, the specimenis illuminated from the side and notfrom above through the objectivelens as before. With the traditionalconfiguration, researchers obtainedexcellent resolution in the microscopeslide, but the resolution perpendicu-lar to the slide is worse. With theSPIM procedure, an extremely thin“light sheet” is generated in thespecimen so that an optical sectionalimage is created. A special feature ofSPIM is that only one plane is illumi-

searchers to delve deeper into thetissue. The entire process is very fastand the image information generatedcan be pieced together using appro-priate software to form a high-reso-lution 3D image. It is the perfectcomplement to confocal and multi-photon 3D imaging systems.

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nated and observed at a time unlikein conventional or confocal micro-scopes in which the entire specimenis exposed for each plane. For exam-ple, if 100 planes have to be record-ed, the radiation exposure to thespecimen is reduced to 1% of whatwas previously required. This advan-tage can be used to significantly in-crease the period of observation. Thesectional images can be recordedfrom several sides by moving orrotating the specimen. This makeshidden regions visible, allowing re-

www.embl.de/ExternalInfo/stelzerwww.zeiss.de/micro

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Tube lens

Detection

Filter

Objective

Specimen

Light sheet

Cylindrical lensCollimatorLightguide

from laser

Illumination

Camera

polecells

somatic cells

yolk

20�mA

B

xy

5


7

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Fig. 4:Three-dimensional imagerendition of the pictureseries from Fig. 5:left 180°, right fusion.

Fig. 5:Drosophila embryo,pole cells, x-y plane.

Fig. 6:Drosophila embryo,pole cells, y-z plane.

Fig. 7:Picture series of Medakafish embryos from variousperspectives.

Fig. 8:Drosophila larva:(a) Traditional image(b) Theta illumination

of a single plane(c) Image stack(d) Image stack rotated

180° around the vertical axis.

polecells

B

A

zy

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SPIM Principle:beam path and opticalcomponents.

(a) (b) (c) (d)

200 �m


Fig. 1:The ergonomic design ofthe surgical microscopeallows the surgeon to workin an extremely comfortableposition over longerperiods.


preserve the mobility and dynamicsof the spine, particularly with symp-toms of wear.

Considering the cost pressuresfacing the healthcare sector, whatopportunities and innovations areparticularly important from yourpoint of view?

Any procedure that is consideredminimally invasive is particularly im-portant, i. e. all microsurgical and en-doscopic procedures. In fact, we havebeen using minimally invasive meth-ods in Germany for 15 years. Howev-er, it was only after healthcare reformthat the positive effects had their fullimpact. Patients are released earlierfrom the hospital, i. e. the more gen-tle the operation, the shorter the stayand the faster the patient can berehabilitated.

What is required for minimallyinvasive surgery?

There can be no minimally invasivesurgery without visualization systems.Minimally invasive surgery is onlypossible if optical aids are available,e. g. a surgical microscope. Throughtiny incisions, these instruments pro-

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Dr. Mayer, what developmentsand changes have you noticed inrecent years concerning spinediseases?

The range of spine diseases haschanged so that now primarily olderpeople have to undergo surgery onthe spine. There are many differenttypes

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