Useful Data for Astrophotographers




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Frame Dimensions, Limiting Magnitude and Unguided Trailing Guidelines
Maximum Exposure Before Trailing
Lens Focal Length
35mm Frame Size
Limiting Magnitude
Width of Moon on Film
Equatorial Region of Sky
Polar Region
20mm
82° x 55°
8.5
30
40
24mm
71° x 48°
9
25
35
28mm
63° x 44°
9.5
22
30
35mm
51° x 34°
10
17
26
50mm
38° x 26°
11
0.5mm
12
18
85mm
23° x 15°
12
0.8mm
7
11
135mm
14.5° x 9.5°
13
1.2mm
5
8
180mm
11° x 7°
13.5
1.6mm
3
6
300mm
6.5° x 4.4°
14
2.7mm
2
3
500mm
3.9° x 2.6°
14.5
4.6mm
1,000mm
2.0° x 1.3°
16.5
9mm


Deep-Sky Exposure Guidelines for Better 400-to-1,000-Speed Print Films (Unhypered)

Conditions
f2.0
f2.8
f4.0
f5.6
f8
noticeable horizon glow
1-4 min.
3-6 min.
8-15 min.
20-40 min.
30-60 min.
deep rural with little horizon glow
3-6 min.
5-12 min.
12-30 min.
25-60 min.
as long as possible
exceptionally dark high-altitude site
4-10 min.
8-18 min.
20-40 min.
as long as possible
as long as possible

The "better" films are Fuji SG+ 800, Kodak Pro 1000 PZM, Kodak Ektapress Multispeed PJM 640, Kodak Pro 400 PPF and Fuji SG+ 400. Exposures can be cut by up to half if temperature is below 0 degrees C (32° F). Increase exposure times when lenses shorter than 20mm focal length.

Deep-Sky Exposure Guidelines for Better Slide Films (Unhypered)

Conditions
f2.0
f2.8
f4.0
f5.6
noticeable horizon glow
2-5 min.
5-12 min.
10-18 min.
20-40 min.
deep rural with little horizon glow
4-8 min.
10-20 min.
20-40 min.
as long as possible
exceptionally dark high-altitude site
5-12 min.
15-35 min.
25-60 min.
as long as possible

The "better" films are Kodak Ektachrome P1600, Kodak Elitechrome II 100 (both films should be pushed up one or two stops during processing). Exposures can be cut by up to half if temperature is below 0 degrees C (32° F). Increase exposure times when lenses shorter than 20mm focal length.
Data above adapted from Splendors of the Universe by Terrence Dickinson and Jack Newton. 1997 Firefly books ISBN 1-55209-141-4
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