The Pentax smc Pentax-FA 31mm f/1.8 AL Limited is a 31 mm prime lens with a maximum aperture of f/1.8 for the Pentax KAF2 mount. Here are its field of view on different sensors, hyperfocal distances, Milky Way exposure limits and the cameras it fits.
Focal length
31 mm
Max aperture
f/1.8
Mount
Pentax KAF2
Designed for
Full frame
Field of view by sensor
| Sensor | Diagonal angle of view | 35 mm equivalent |
|---|---|---|
| Full frame | 69.8° | 31 mm |
| APS-C (1.5×) | 49.0° | 47 mm |
| Canon APS-C (1.6×) | 47.1° | 50 mm |
| Micro Four Thirds | 38.5° | 62 mm |
Hyperfocal distance
| Focal length | f/2.8 | f/5.6 | f/8 | f/11 | f/16 |
|---|---|---|---|---|---|
| 31 mm | 11 m | 5.8 m | 4.0 m | 2.9 m | 2.0 m |
Circle of confusion 0.030 mm (sensor size the lens is designed for).
Longest exposure for sharp stars
| Camera | NPF rule (wide open) | 500 rule |
|---|---|---|
| Full frame (24 MP) | 7.7 s @ f/1.8 | 16.1 s |
| Full frame (45 MP) | 6.3 s @ f/1.8 | 16.1 s |
| APS-C (24 MP) | 5.8 s @ f/1.8 | 10.5 s |
Cameras that fit (43)
- Pentax 35mm film: full frame
- Pentax *ist DL2
- Pentax *ist DL
- Pentax *ist DS2
- Pentax *ist DS
- Pentax *ist D
- Pentax K-m
- Pentax K100D
- Pentax K100D Super
- Pentax K110D
- Pentax K10D
- Pentax K20D
- Pentax K-30
- Pentax K-50
- Pentax K-500
- Pentax K-7
- Pentax K-52010
- Pentax K-5 II2012
- Pentax K-5 IIs
- Pentax K-32013
- Pentax K-3 II2015
- Pentax K-3 III2021
- Pentax K-3 III Monochrome
- Pentax K2000
- Pentax K200D
- Pentax K-x
- Pentax K-r
- Pentax K-S2
- Pentax K-S1
- Pentax K-01
- Pentax KF2022
- Pentax KP2017
- Samsung GX10
- Samsung GX20
- Samsung GX-1S
- Samsung GX-1L
- Pentax K-12016
- Pentax K-1 II2018
- Pentax K-702016
- KMZ Zenit 122K
- KMZ Zenit 212K
- KMZ Zenit 312K
- KMZ Zenit KM
Where to buy
B&H PhotoAmazonKEH (used)MPB (used)FAQ
What is the Pentax smc Pentax-FA 31mm f/1.8 AL Limited equivalent to on APS-C?
About 46 mm (1.5×) or 50 mm on Canon APS-C (1.6×).
Which cameras is the Pentax smc Pentax-FA 31mm f/1.8 AL Limited compatible with?
It fits Pentax 35mm film: full frame, Pentax *ist DL2, Pentax *ist DL, Pentax *ist DS2, Pentax *ist DS and more (see the full list above).