Pentax SMC FA 31mm f/1.8 AL Limited - Lab Test / Review
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Review by Klaus Schroiff, published May 2012

Special thanks to Knut Kampe for providing this lens!


We already tested the Pentax SMC FA 31mm f/1.8 AL Limited a couple of years ago based on the Pentax K10D (@10mp) but for as another reference test we've just re-tested it again on the Pentax K5 (@16mp). Most of the findings remain valid on the K5 so please forgive us for having reused most of the old review here again.

The Pentax SMC FA 31mm f/1.8 AL Limited is the most pronounced wide angle of classic FA Limited lenses. Similar to its cousins, it offers an absolutely superb build quality ... at a very high price. However, to be fair the ultra-large aperture (for a wide-angle lens) is also off the mainstream and quality simply doesn't come for free. Typical for all FA lenses it supports the full 35mm format so it can be used both on film and digital SLRs. On Pentax DSLRs its field-of-view is equivalent to about 47mm (full format) so within this scope the lens gets transformed to a "standard" lens.

The build quality of the lens is exceptional with all parts made of metal. The small focus ring operates very smoothly and slightly damped. Typical for FA-type lenses there's still a dedicated aperture ring on the lens. The FA 31mm f/1.8 extends a little when focusing towards close distances. Pentax also implemented a built-in flower shaped hood which cannot be removed. The lens is/was available both in a silver- and black-colored variant. Unlike its cousins it isn't really a small nor overly light-weight lens.

The FA 31mm f/1.8 has no internal AF motor and relies on a slotted drive screw operated by the camera. As a result AF operation will generate a moderate degree of noise. The AF speed is very fast on the K5.

Equiv. focal length46.5 mm (full format equivalent)
Equiv. aperturef/2.7 (full format equivalent, in terms of depth-of-field)
Optical construction9 elements in 7 groups inc. 1 aspherical, 1 ED and 1 HRLD element
Number of aperture blades9
min. focus distance0.3 m (max. magnification ratio 1:6.25)
Dimensions65 x 69 mm
Weight345 g
Filter size58 mm (non-rotating)
Hoodbuilt-in, flower-shaped
Other features-

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