The Pentax K-3 uses the Pentax KAF2 mount with a 1.53× crop factor (about 23.5 × 15.6 mm sensor), 24.3 megapixels, announced in 2013. 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 |
|---|---|---|---|
| 8 mm | 12 mm | 120.9° | 111.5° |
| 10 mm | 15 mm | 109.3° | 99.2° |
| 12 mm | 18 mm | 99.2° | 88.8° |
| 14 mm | 21 mm | 90.4° | 80.0° |
| 16 mm | 25 mm | 82.8° | 72.6° |
| 18 mm | 28 mm | 76.2° | 66.3° |
| 20 mm | 31 mm | 70.4° | 60.9° |
| 24 mm | 37 mm | 60.9° | 52.2° |
| 28 mm | 43 mm | 53.5° | 45.5° |
| 35 mm | 54 mm | 43.9° | 37.1° |
| 50 mm | 77 mm | 31.5° | 26.4° |
| 85 mm | 130 mm | 18.8° | 15.7° |
| 135 mm | 207 mm | 11.9° | 9.9° |
| 200 mm | 307 mm | 8.1° | 6.7° |
| 300 mm | 460 mm | 5.4° | 4.5° |
| 400 mm | 614 mm | 4.0° | 3.4° |
Multiply by the 1.53× 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 | 22.4 s | 26.8 s | 14.5 s | 40.7 s |
| 10 mm | 17.9 s | 21.4 s | 11.6 s | 32.6 s |
| 12 mm | 14.9 s | 17.9 s | 9.7 s | 27.2 s |
| 14 mm | 12.8 s | 15.3 s | 8.3 s | 23.3 s |
| 16 mm | 11.2 s | 13.4 s | 7.3 s | 20.4 s |
| 18 mm | 10.0 s | 11.9 s | 6.5 s | 18.1 s |
| 20 mm | 9.0 s | 10.7 s | 5.9 s | 16.3 s |
| 24 mm | 7.5 s | 8.9 s | 4.9 s | 13.6 s |
| 28 mm | 6.4 s | 7.7 s | 4.2 s | 11.6 s |
| 35 mm | 5.1 s | 6.1 s | 3.4 s | 9.3 s |
NPF = (35 × f-number + 30 × pixel pitch) ÷ focal length, with a pixel pitch of 3.88 µm (from 24.3 MP). 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 | 1.8 m | 0.9 m | 0.6 m | 0.5 m | 0.3 m |
| 14 mm | 3.6 m | 1.8 m | 1.3 m | 0.9 m | 0.6 m |
| 16 mm | 4.7 m | 2.3 m | 1.6 m | 1.2 m | 0.8 m |
| 18 mm | 5.9 m | 3.0 m | 2.1 m | 1.5 m | 1.1 m |
| 20 mm | 7.3 m | 3.7 m | 2.6 m | 1.9 m | 1.3 m |
| 24 mm | 11 m | 5.3 m | 3.7 m | 2.7 m | 1.9 m |
| 28 mm | 14 m | 7.2 m | 5.0 m | 3.7 m | 2.5 m |
| 35 mm | 22 m | 11 m | 7.8 m | 5.7 m | 3.9 m |
| 50 mm | 46 m | 23 m | 16 m | 12 m | 8.0 m |
Focus at the hyperfocal distance and everything from half that distance to infinity is acceptably sharp (circle of confusion 0.0196 mm). Use the hyperfocal calculator for other settings.
Maximum print size
| Print resolution | Inches | Centimeters |
|---|---|---|
| 150 ppi | 40.2 × 26.8 in | 102 × 68 cm |
| 200 ppi | 30.2 × 20.1 in | 77 × 51 cm |
| 240 ppi | 25.2 × 16.8 in | 64 × 43 cm |
| 300 ppi | 20.1 × 13.4 in | 51 × 34 cm |
300 ppi suits close viewing; 150–200 ppi is plenty for large prints viewed from a distance.
Compatible lenses (190 in our database)
Native and adapter-free compatible lenses from the Lensfun database. Third-party and adapted lenses may also work.
How to check the Pentax K-3 shutter count
Pentax and Ricoh DSLRs store the count in MakerNotes; ExifTool decodes it with `exiftool -ShutterCount image.dng`.
ExifTool tag: ShutterCount. 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)Other Pentax KAF2 cameras
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