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: 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.