The Sigma SD15 uses the Sigma SA mount with a 1.74× crop factor (about 20.7 × 13.8 mm sensor). Below: equivalent focal lengths, maximum shutter speeds for sharp stars, a hyperfocal distance chart, compatible lenses and how to check the shutter count.
Mount
Sigma SA
Crop factor
1.74×
Sensor (approx.)
20.7 × 13.8 mm
Circle of confusion
0.0173 mm
Equivalent focal length & field of view
Lens focal length
Full-frame equivalent
Diagonal FOV
Horizontal FOV
8 mm
14 mm
114.5°
104.6°
10 mm
17 mm
102.4°
92.0°
12 mm
21 mm
92.1°
81.6°
14 mm
24 mm
83.2°
72.9°
16 mm
28 mm
75.7°
65.8°
18 mm
31 mm
69.3°
59.8°
20 mm
35 mm
63.8°
54.7°
24 mm
42 mm
54.8°
46.7°
28 mm
49 mm
47.9°
40.6°
35 mm
61 mm
39.1°
32.9°
50 mm
87 mm
27.9°
23.4°
85 mm
148 mm
16.7°
13.9°
135 mm
235 mm
10.5°
8.8°
200 mm
348 mm
7.1°
5.9°
300 mm
522 mm
4.7°
4.0°
400 mm
696 mm
3.6°
3.0°
Multiply by the 1.74× crop factor for the full-frame equivalent field of view.
Milky Way exposure: NPF and 500 rule
Focal length
NPF @ f/1.8
NPF @ f/2.8
Strict NPF @ f/2.8
500 rule
8 mm
20.2 s
24.6 s
13.3 s
35.9 s
10 mm
16.2 s
19.7 s
10.7 s
28.8 s
12 mm
13.5 s
16.4 s
8.9 s
24.0 s
14 mm
11.6 s
14.1 s
7.7 s
20.5 s
16 mm
10.1 s
12.3 s
6.7 s
18.0 s
18 mm
9.0 s
10.9 s
6.0 s
16.0 s
20 mm
8.1 s
9.8 s
5.4 s
14.4 s
24 mm
6.8 s
8.2 s
4.5 s
12.0 s
28 mm
5.8 s
7.0 s
3.9 s
10.3 s
35 mm
4.6 s
5.6 s
3.1 s
8.2 s
NPF = (35 × f-number + 30 × pixel pitch) ÷ focal length, with a pixel pitch of 3.3 µm (typical for this format — exact resolution not in our database). The strict version (Michaud's detailed NPF for the galactic core) gives pin-point stars at 100% view; the 500 rule is a loose rule of thumb that shows trailing on modern sensors.
Hyperfocal distance chart
Focal length
f/2.8
f/5.6
f/8
f/11
f/16
10 mm
2.1 m
1.0 m
0.7 m
0.5 m
0.4 m
14 mm
4.1 m
2.0 m
1.4 m
1.0 m
0.7 m
16 mm
5.3 m
2.7 m
1.9 m
1.4 m
0.9 m
18 mm
6.7 m
3.4 m
2.4 m
1.7 m
1.2 m
20 mm
8.3 m
4.1 m
2.9 m
2.1 m
1.5 m
24 mm
12 m
6.0 m
4.2 m
3.1 m
2.1 m
28 mm
16 m
8.1 m
5.7 m
4.1 m
2.9 m
35 mm
25 m
13 m
8.9 m
6.5 m
4.5 m
Focus at the hyperfocal distance and everything from half that distance to infinity is acceptably sharp (circle of confusion 0.0173 mm). Use the hyperfocal calculator for other settings.
Native and adapter-free compatible lenses from the Lensfun database. Third-party and adapted lenses may also work.
How to check the Sigma SD15 shutter count
Not every maker writes a shutter count into image files. Try `exiftool -a -G1 -s image` on an unedited original and look for a tag containing "Shutter" or "Count".
ExifTool tag: (varies). Always test an original, unedited file straight from the card.
1.74×. A 24 mm lens frames like a 42 mm lens on full frame.
What shutter speed should I use for the Milky Way with the Sigma SD15?
With a 8 mm lens at f/2.8, about 25 seconds keeps stars sharp (NPF rule).
How do I check the shutter count on the Sigma SD15?
Not every maker writes a shutter count into image files. Try `exiftool -a -G1 -s image` on an unedited original and look for a tag containing "Shutter" or "Count".
Which lenses fit the Sigma SD15?
Lenses for the Sigma SA mount — 75 are listed above.
