Pentax FA 31mm Limited lens
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 | |
| Maker | Pentax |
|---|---|
| Technical data | |
| Type | Prime |
| Focus drive | Screwdrive |
| Focal length | 31mm |
| Focal length (35mm equiv.) | 46.5mm |
| Aperture (max/min) | f/1.8 / f/22 |
| Close focus distance | 12 inches (30 cm) |
| Max. magnification | 0.16x |
| Diaphragm blades | 9 |
| Construction | 9 elements in 7 groups |
| Features | |
| Application | Normal lens (APS-C), Wide-angle lens (Full frame) |
| Physical | |
| Max. length | 2.7 inches (69 mm) |
| Diameter | 2.6 inches (66 mm) |
| Weight | 12.2 ounces (350 g) |
| Filter diameter | 58mm |
| Accessories | |
| Lens hood | Built-in |
| Angle of view | |
| Diagonal | 70° (full frame), 50° (APS-C) |
| Retail info | |
| MSRP | 1,299.95 USD USD |
The SMC Pentax-FA 31mm f/1.8 AL Limited is a full-frame moderate wide-angle lens for Pentax K-mount. On an APS-C camera, it gives a normal field of view. It lacks Quick Shift Focus, which is now found on most other Pentax lenses, and therefore does not allow manual focusing while in autofocus mode.
The eventual design of this lens was the second major attempt. An earlier design by Jun Hirakawa of a smaller 31mm f/2.4 lens was rejected by management for being too "slow" (i.e. too narrow at maximum aperture), and so the f/1.8 version came to be developed by Takayuki Ito and Masayuki Murata.[1]
