The KMZ Zenit 312K uses the Pentax K mount with a 1.00× crop factor (about 36.0 × 24.0 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
Pentax K
Crop factor
1.00×
Sensor (approx.)
36.0 × 24.0 mm
Circle of confusion
0.03 mm
Equivalent focal length & field of view
Lens focal length
Full-frame equivalent
Diagonal FOV
Horizontal FOV
10 mm
10 mm
130.4°
121.9°
12 mm
12 mm
122.0°
112.6°
14 mm
14 mm
114.2°
104.3°
16 mm
16 mm
107.0°
96.7°
18 mm
18 mm
100.5°
90.0°
20 mm
20 mm
94.5°
84.0°
24 mm
24 mm
84.1°
73.7°
28 mm
28 mm
75.4°
65.5°
35 mm
35 mm
63.4°
54.4°
50 mm
50 mm
46.8°
39.6°
85 mm
85 mm
28.6°
23.9°
135 mm
135 mm
18.2°
15.2°
200 mm
200 mm
12.3°
10.3°
300 mm
300 mm
8.2°
6.9°
400 mm
400 mm
6.2°
5.2°
600 mm
600 mm
4.1°
3.4°
Multiply by the 1.00× 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
10 mm
24.0 s
27.5 s
14.8 s
50.0 s
12 mm
20.0 s
22.9 s
12.3 s
41.7 s
14 mm
17.1 s
19.6 s
10.6 s
35.7 s
16 mm
15.0 s
17.2 s
9.3 s
31.2 s
18 mm
13.3 s
15.3 s
8.3 s
27.8 s
20 mm
12.0 s
13.8 s
7.4 s
25.0 s
24 mm
10.0 s
11.5 s
6.2 s
20.8 s
28 mm
8.6 s
9.8 s
5.3 s
17.9 s
35 mm
6.9 s
7.9 s
4.3 s
14.3 s
50 mm
4.8 s
5.5 s
3.0 s
10.0 s
NPF = (35 × f-number + 30 × pixel pitch) ÷ focal length, with a pixel pitch of 5.9 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
14 mm
2.3 m
1.2 m
0.8 m
0.6 m
0.4 m
16 mm
3.1 m
1.5 m
1.1 m
0.8 m
0.5 m
18 mm
3.9 m
1.9 m
1.4 m
1.0 m
0.7 m
20 mm
4.8 m
2.4 m
1.7 m
1.2 m
0.9 m
24 mm
6.9 m
3.5 m
2.4 m
1.8 m
1.2 m
28 mm
9.4 m
4.7 m
3.3 m
2.4 m
1.7 m
35 mm
15 m
7.3 m
5.1 m
3.7 m
2.6 m
50 mm
30 m
15 m
10 m
7.6 m
5.3 m
Focus at the hyperfocal distance and everything from half that distance to infinity is acceptably sharp (circle of confusion 0.03 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 KMZ Zenit 312K 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.
1.00×. A 24 mm lens frames like a 24 mm lens on full frame.
What shutter speed should I use for the Milky Way with the KMZ Zenit 312K?
With a 10 mm lens at f/2.8, about 28 seconds keeps stars sharp (NPF rule).
How do I check the shutter count on the KMZ Zenit 312K?
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 KMZ Zenit 312K?
Lenses for the Pentax K mount and compatible mounts (Pentax KA, Pentax KAF, Pentax KAF2) — 190 are listed above.
