The Phase One P 25 uses the Mamiya 645 mount with a 0.58× crop factor (about 62.4 × 41.6 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.
Equivalent focal length & field of view
| Lens focal length | Full-frame equivalent | Diagonal FOV | Horizontal FOV |
|---|---|---|---|
| 18 mm | 10 mm | 128.7° | 120.0° |
| 20 mm | 12 mm | 123.9° | 114.7° |
| 24 mm | 14 mm | 114.8° | 104.9° |
| 28 mm | 16 mm | 106.5° | 96.2° |
| 35 mm | 20 mm | 93.9° | 83.4° |
| 50 mm | 29 mm | 73.7° | 63.9° |
| 85 mm | 49 mm | 47.6° | 40.3° |
| 135 mm | 78 mm | 31.0° | 26.0° |
| 200 mm | 115 mm | 21.2° | 17.7° |
| 300 mm | 173 mm | 14.2° | 11.9° |
| 400 mm | 231 mm | 10.7° | 8.9° |
| 600 mm | 346 mm | 7.2° | 6.0° |
Multiply by the 0.58× 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 |
|---|---|---|---|---|
| 18 mm | 13.3 s | 15.3 s | 8.3 s | 48.1 s |
| 20 mm | 12.0 s | 13.8 s | 7.4 s | 43.3 s |
| 24 mm | 10.0 s | 11.5 s | 6.2 s | 36.1 s |
| 28 mm | 8.6 s | 9.8 s | 5.3 s | 30.9 s |
| 35 mm | 6.9 s | 7.9 s | 4.3 s | 24.8 s |
| 50 mm | 4.8 s | 5.5 s | 3.0 s | 17.3 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 |
|---|---|---|---|---|---|
| 24 mm | 4.0 m | 2.0 m | 1.4 m | 1.0 m | 0.7 m |
| 28 mm | 5.4 m | 2.7 m | 1.9 m | 1.4 m | 1.0 m |
| 35 mm | 8.4 m | 4.2 m | 3.0 m | 2.2 m | 1.5 m |
| 50 mm | 17 m | 8.6 m | 6.1 m | 4.4 m | 3.1 m |
Focus at the hyperfocal distance and everything from half that distance to infinity is acceptably sharp (circle of confusion 0.052 mm). Use the hyperfocal calculator for other settings.
Compatible lenses (10 in our database)
| Lens | Focal length | Max aperture | Mount |
|---|---|---|---|
| Schneider-Kreuznach 28mm Digitar f/2.8 | 28 mm | f/2.8 | Mamiya 645 |
| Mamiya 35mm f/3.5 | 35 mm | f/3.5 | Mamiya 645 |
| Mamiya 35mm f/22.0-3.5 | 35 mm | f/22 | Mamiya 645 |
| Mamiya 55-110mm f/4.5 | 55–110 mm | f/4.5 | Mamiya 645 |
| Schneider-Kreuznach LS 55mm f/2.8 | 55 mm | f/2.8 | Mamiya 645 |
| Mamiya 80mm f/2.8 | 80 mm | f/2.8 | Mamiya 645 |
| Schneider-Kreuznach LS 80mm f/2.8 | 80 mm | f/2.8 | Mamiya 645 |
| Schneider-Kreuznach LS 110mm f/2.8 | 110 mm | f/2.8 | Mamiya 645 |
| Mamiya 120mm f/32.0-4.0 | 120 mm | f/32 | Mamiya 645 |
| Mamiya 150mm f/32.0-3.5 | 150 mm | f/32 | Mamiya 645 |
Native and adapter-free compatible lenses from the Lensfun database. Third-party and adapted lenses may also work.
How to check the Phase One P 25 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.
Where to buy
Compare new and used prices at these retailers:
B&H PhotoAmazonKEH (used)MPB (used)