Astrophotography

The Basics

Image Capture Devices

Digital Compact cameras Webcams Digital SLR cameras Astronomical CCD cameras

Digital Compact Cameras

Advantages Inexpensive Easy to use Small size Low weight No computer or

external power supply needed

Disadvantages Lens not

replaceable Often, automatic

modes cannot be switched off

Mounting to telescope not easy

Digital Compact Cameras

More Advantages Fast, automatic

operation

More Disadvantages Lack of features

No bulb setting

Limited to 15 to 30 sec. exposure

Webcams

Advantages Inexpensive High sensitivity,

short exposure times

High resolution, sharp details

Color images

Disadvantages Tiny sensor,

small field of view No bulb

exposures possible

No cooling to reduce noise

Huge amounts of data

Webcams

More Advantages Good focus

control No cable release

tangle Unbeatable for

planetary imaging

More Disadvantages Losses through

data compression Operation

impossible without computer

Operation without telescope not reasonable

Digital SLR's

Advantages Easy to use No computer

necessary Versatile Color images Suitable for large

objects

Disadvantages Relatively high

noise for long exposures

High power consumption

Difficulty focusing using LCD screen

Digital SLR's

More Advantages Results can be

viewed immediately

Automatically records exposure data

Flat exposure surface as opposed to film

More Disadvantages Due to color

data, lower resolution than black and white CCD camera

Limited red sensitivity through IR blocking filter

Digital SLR's

More Advantages Easy adjustment

of ISO speed

More Disadvantages In camera image

processing that is detrimental to astrophotos (even in raw)

Astronomical CCD Cameras

Advantages Low noise due to

sensor cooling Large dynamic

range High resolution

with monochrome sensor

True raw data

Disadvantages Complex handling Computer required Time consuming

for color shots Use limited to

astrophotography Difficulty in setting

and focusing

Astronomical CCD Cameras

More Advantages High spectral

sensitivity, shorter exposure

Good guiding capabilities

No camera shake due to hands off operation

Maximum image quality

More Disadvantages High priced

Notes and Tips

Digital cameras allow for shorter exposure times than film cameras

You can find samples of pictures taken with different camera types at: www.astromeeting.de/astrophotography_digital.htm

Telescopes with focal lengths of 500mm – 1000mm are recommended

Step by Step Path to Astrophotography

Scenic snapshots – Tripod and camera Piggyback – Mount camera on telescope tube Images though telescope eypiece – Afocal

photography Webcam through telescope Deep-Sky Images

DSLR Astronomical CCD Tracking mount

Notes and Tips

Large focal ratio (F-Stop number is larger) telescopes are best suited for planetary photography

Low focal ratio (F-Stop number is smaller) telescopes are best suited for deep-sky photography

For astrophotography not only are the number of megapixels important, but also the dimensions of the sensor and the dimensions of the individual pixels

Resolving Power of Telescopes

60 mm = 2.2” 80 mm = 1.6” 100 mm = 1.3” 130 mm = 1.0” 150 mm = 0.9” 200 mm = 0.7” 250 mm = 0.5” 300 mm = 0.4

Angle of View

To get the best results for your astrophotography you need to know the angle of view for a particular combination of lens, telescope, and camera combination.

Angle of View Formula

If you know the edge length of the image sensor and the effective focal length of the optics you can determine the angle of view with this formula:

Angle of View = 2 x Artan(L / 2*F) L = edge length of imaging sensor F = effective focal length in mm

Focal Length Formula

If you want to determine the focal length needed to fill your frame you can use this formula:

F = L / 2*Tan(Angle of View / 2) F = Focal length L = Edge length of imaging sensor in mm Angle of View = Angle of view of object you are

trying to photograph

Ideal Magnification for Planetary Astrophotography

N > Dpixel / .2805 N = Dnominator of focal ratio (F-Stop) Dpixel = edge length of a single pixel in

micons (um) Gives you the optimal focal ratio to get the

maximum resolution from your telescope (see telescope resolution slide) when taking astropohotos of sun, moon, or planets

Ideal Magnification for Deep-Sky Objects

F = 413 * Dpixel / S F = Focal length in mm Dpixel = Edge length of a single pixel in

micons (um) S = Maximum expected resolution in

arcseconds on a particular night, due to atmospheric turbulence (seeing). If you do nhot have an excellent dark-sky observing site, then you should estimate a maximum resolution of 4 arcseconds.