Pentax SMC-DA 21mm f/3.2 AL Limited - Review / Test Report
Lens Reviews - Pentax

Review by Klaus Schroiff, published May 2007

Special thanks to Patrick Pihl for providing this lens!


The Pentax SMC-DA 21mm f/3.2 AL Limited is one of three so-called pancakes lenses in the current Pentax lens lineup. As you can observe below pancake lenses are pretty tiny beings - the DA 21mm has a length of merely 25mm. The species is not overly popular when looking at the whole industry. Nikon used to have one but it has already been discontinued again and none of the others offer one. Pancakes have advantages and disadvantages. They're obviously as small and light-weight as it gets. Optically they're contra light masters due to the low number of lens elements (and therefore surfaces) and they tend to produce a relatively even image. On the downside they have a comparatively slow max. aperture and the peak performance tends to be a little lower compared to conventional lenses - the theory tells that the degree of correction increases the more elements you add to the design ... assuming you do it right (there're limits to this specifically in terms of production quality). The DA 21mm f/3.2 is a dedicated APS-C lens so it can only be used on Pentax (and Samsung) DSLRs. Its field-of-view is equivalent to 32mm (full format) so it can be regarded as a perfect for street photography - a classic sweet spot of the Pentax system.

The DA 21mm is a Limited lens which means that Pentax uses quality material, a mainly manual assembly and an above average quality control (they say). The lens is certainly a very high quality item with all parts made of metal and tight tolerances. The tiny focus ring operates smooth and slightly damped. As you can see below the lens extends a marginally when focusing towards closer distances. The front element does not rotate so using a polarizer is no problem. We received a user report that it is not possible to use a filter and the lens hood at the same time because the filter prevents the hood from locking at its intended position.

Typical for most Pentax lenses the DA 21mm f/3.2 has no internal AF motor and relies on a slotted drive screw operated by the camera. Consequently AF operations generate a moderate degree of noise. The AF speed is very fast on the K10D - finally the focus group is about as light-weight as it gets. Thanks to a "Quick-Shift Focus System" manual focusing is instantly possible once the AF has achieved focus - this works very well and noiseless.

Equiv. focal length32 mm (full format equivalent)
Equiv. aperturef/4.8 (full format equivalent, in terms of depth-of-field)
Optical construction8 elements in 5 groups inc. 1 aspherical element
Number of aperture blades7
min. focus distance0.2 m (max. magnification ratio 1:5.9)
Dimensions63 x 25 mm
Weight140 g
Filter size49 mm (non-rotating)
Other featuresfloating element for close focus correction