optical systems design with zemax...

Optical Systems Design with Zemax OpticStudio

Lecture 1

Why Optical Systems Design

Optical system design is no longer a skill reserved for a few professionals. With readily available commercial optical design software, these tools are accessible to the general optical engineering community and rudimentary skills in optical design are now expected by a wide range of industries who utilize optics in their products.

Optical Systems Design 2

Course Aims

To introduce the design principles of lens and mirror optical systems and the evaluation of designs using modern computer techniques. The lectures will cover lens design, aberrations, optimization, tolerancing and image quality metrics.


ZEMAX Optics Studio The ZEMAX optical design program is a comprehensive software tool. It integrates all the features required to conceptualize, design, optimize, analyze, tolerance, and document virtually any optical system. It is widely used in the optics industry as a standard design tool. This course will introduce the basics of ZEMAX using the recently released (2014) OpticStudio interface.


Other Optical Design Software

•  Code-V (Optical Research Associates) •  OSLO (Sinclair Optics) •  OpTaliX (Optenso Ltd) •  ASAP (Breault Research) •  TracePro (Lambda Research) •  FRED (Photon Engineering)


Local Experts

•  Stephen Rolt •  Jurgen Schmoll •  Ariadna Calcines

•  Colin Dunlop •  Tim Morris

•  Undoubtedly others …


Course Outline

•  Lecture 1: Introduction •  Lecture 2: Sequential Systems •  Lecture 3: Optimization •  Lecture 4: Tolerancing •  Lecture 5: Non-sequential & other stuff


Web page: http://astro.dur.ac.uk/~rsharp/opticaldesign.html

Objectives: Lecture 1 At the end of this lecture you should: 1.  Be able to install a version of the Zemax optical

design programme on a Windows PC 2.  Understand the main tasks involved in optical

systems design with Zemax 3.  Be aware of Zemax notation for the 5 main Seidel

aberrations 4.  Know the relevance of the terms: optical axis,

stop, pupil, chief ray, marginal ray, point spread function for Zemax

5.  Use the Zemax lens data editor to enter the specifications of a simple lens


Getting started •  Download a current copy of OpticStudio from:

http://www.zemax.com/support/downloads/ •  CfAI/Atmol members can use the shared license

server on zemax.cfai.local. This requires a copy of the file sntlconfig.xml from the server Exchange/installers/Zemax to be copied into the main OpticsStudio directory (C:\Program Files\Zemax OpticStudio)

•  Five licences are available. See who is using them at: http://zemax.cfai.local:7002

•  Log out from Zemax if not actively using! •  Non-CfAI/Atmol members should download the

OpticStudio demo


Recommended Texts •  OpticStudio User Manual and Getting Started Using

OpticStudio (access from programme help) •  Introduction to Lens Design with Practical Zemax

Examples, Joseph M Geary (Willmann-Bell Inc.) •  Optical Systems Design, Robert Fischer & Bijana

Tadic(SPIE Press) •  Practical Computer-Aided Design, Gregory Hallock-

Smith (Willmann-Bell Inc.) •  Astronomical Optics, Dan Schroeder (Academic Press;

GoogleBooks) •  Optics, Jeff Hecht (Addison Wesley)


Also the Zemax knowledge base: http://www.zemax.com/support/knowledgebase

Optical Systems Design

‘Science or art of developing optical systems to image, direct, analyse or measure light.’ •  Includes camera lenses, telescopes, microscopes, scanners, photometers, spectrographs, interferometers, … •  Systems should be as free from geometrical optical errors (aberrations) as possible. •  Correcting and controlling aberrations is one of the main tasks of the optical designer (includes performance evaluation and fabrication/tolerancing issues).


Historical Note •  Lens design has changed significantly since

~1960 with the introduction of digital computers and numerical optimisation.

•  Equations describing aberrations of lens/mirror systems are very non-linear functions of system parameters (curvatures, spacings, refractive indices, dispersions, …)

•  Only a few specialised systems can be derived analytically in exact closed-form solutions.

•  Analytical design methods (Petzval, Seidel) were historically based on a mathematical treatment of geometrical imagery and primary aberrations – still useful for initial designs.

•  Numerical evaluation methods ray trace many light rays from object to image space.


Seidel (3rd order) Aberrations

1.  Spherical aberration 2.  Coma 3.  Astigmatism 4.  Field curvature 5.  Distortion


6.  Longitudinal chromatic aberration 7.  Lateral chromatic aberration

Numerical Evaluation Methods

•  Assume only trigonometry, law of reflection and Snell’s law

•  •  For each ray calculate new ray parameters at each

surface •  Sequential ray-tracing assumes that light travels

from surface to surface in a defined order. •  Non-sequential ray-tracing does not assume a pre-

defined path for the rays, but when a ray hits a surface in its path, it may then reflect, refract, diffract, scatter or split into child rays (scattered light).


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n1 sinθ1 = n2 sinθ2

Numerical Optimisation Methods

•  Given a starting configuration, the computer can be used to optimise a design by an iterative process.

•  Final image quality is ‘best’ that can be achieved under constraints of basic configuration, required focal length, f/number, field of view, wavelength etc.

•  Programs are still ‘dumb’. Designer must supply intelligence through selection of starting configuration, control of optimization parameters, understanding of underlying optical theory, etc.


Objects, Light Rays & Wavefronts •  Objects composed of self-luminous (radiant) points of

light •  Trajectories of photons from each of these points

define the light rays •  Neglecting diffraction, these physical rays become

geometrical rays (ray bundles) •  Wavefronts are surfaces normal to rays •  Light travel times along all rays to the wavefront from

an object point are the same (for a fixed wavelength) •  Neglecting diffraction, physical wavefronts become

geometrical wavefronts (good approximation except near boundaries or edges)


Objects, Light Rays & Wavefronts


Object Plane

Image Plane

Optical axis Wavefronts

Ray bundles

The Optical Axis

•  Most optical systems are collections of rotationally symmetric surfaces whose centres of curvature are all located along a common axis (Optical Axis)

•  Plane surfaces have infinite radius of curvature •  Intersection of the optical axis and a surface is at

the surface vertex •  Longitudinal cross-section defines a meridional

plane (all equivalent) •  Ray in this plane are meridional rays. Rays out of

plane are skew rays.


Stops & Pupils •  Every optical system contains one physical aperture that

limits the extent of the wavefront for the ray bundle which is transmitted through the system to the on-axis image point (aperture stop or stop)

•  If optics are large enough then this will also be true for off-axis image points

•  In many cases this is not true leading to mechanical vignetting of off-axis image points

•  Size and location of the aperture stop can have important impact on system performance through its effects on geometrical aberrations

•  Image of the stop in object space is the entrance pupil. Image of the stop in image space is the exit pupil.

•  Focal ratio (e.g. f/5.6) is ratio of effective focal length (EFL) to entrance pupil diameter (EPD)


Stops & Pupils


Optical Design (S13) Joseph A. Shaw – Montana State University

4

Demonstration of Pupils with a Camera Lens

View a camera lens from the front and from the back to see the entrance and exit pupils. You are seeing the same iris from both sides, but it appears to be of different diameter because of the intervening optics.

Entrance pupil Exit pupil

Marginal & Chief Rays •  Marginal ray originates at the object point on axis

and goes to the edge of the stop of the system. •  Chief ray (principal ray) originates at the object

point at the edge of the field of view and passes through the centre of the stop of the system.

Axial height (transverse distance away from the optical axis) of the marginal ray is zero at the object and all images of the object. At these locations the axial height of the chief ray determines the size (semi-diameter) of the object and its images (magnification). These roles are reversed when considering the aperture stop and its images (pupils).


Marginal & Chief Rays


Point Spread Function (PSF)

•  Impossible to image a point object as a perfect point image.

•  PSF gives the physically correct light distribution in the image plane including the effects of aberrations and diffraction.

•  Errors are introduced by design (geometrical aberrations), optical and mechanical fabrication & alignment.


Co-ordinate Systems and Sign Conventions

•  No standardization between different codes!

•  Zemax uses a right-handed cartesian co-ordinate system, where the Z-axis is the optical axis and light initially moves in the direction of +Z.

•  Co-ordinate breaks (rotations) are defined in a right-handed sense.


Optical Prescriptions

•  An optical design is described by a set of surfaces through which the light passes sequentially.

•  Surfaces are tabulated in the lens data editor and are numbered sequentially from the object surface (surface 0) and ending with the image surface.

•  A minimum of 3 surfaces is required (object, stop, image).


Surface Parameters

•  Surface number •  Radius of curvature (R) •  Thickness to the next surface (t) •  Glass type in the next medium (or Air if blank) •  Aspheric data (if any) •  Aperture size (semi-diameter D) •  Tilt and decenter data (if any) One surface is designated the stop surface.


Using the Lens Data Editor Setup tab -> System Explorer: •  Aperture: define entrance pupil diameter (50mm) •  Fields: define field angle(s) (FoV) (0 deg) •  Wavelengths: define wavelength(s) of rays (632.8nm) Singlet lens prescription: R1 = 100 mm, t1 = 10 mm, Glass = BK7, Semi-‐D1 = 25 mm R2 = -‐100 mm, t2 = Op9mize-‐>Quick-‐focus, Air, Semi-‐D2 = 25 mm The aperture stop (entrance pupil) is placed at the first lens surface (Diam = 50 mm). May also some*mes use dummy surfaces to help with plots.


ZEMAX Lens Data Editor


ZEMAX System Viewers


System Properties


•  Analyze -‐> Reports:

Summary: Lecture 1 •  Optical design has changed radically since

the introduction of modern ray-tracing software packages

•  ZEMAX is a comprehensive software tool which integrates all the features required to design an optical system

•  The optical design process involves developing a conceptual optial design, ray-tracing an optical layout and varying parameters of the specification to improve performance


Exercises: Lecture 1

•  Install Zemax Optic Studio(or the OpticStudio demo) on your PC

•  Use the lens data editor to input the optical prescription of the biconvex singlet from the lecture

•  Investigate how the focus depends on wavelength and lens curvatures

•  Investigate how the image quality depends on the thickness of the lens


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