Lens review

Pentax smc DA 21 mm f/3.2 AL Limited

15 September 2011
Arkadiusz Olech

3. Build quality

As usual the untypical parameters of the Pentax lenses mean that there are problems if you want to compare the tested lens to any direct rivals. You don’t have to think hard to guess that simply no other company produces a 3.2/21 lens. Out of necessity we have to compare the tested lens to full frame devices with similar but not exactly the same parameters. An appropriate comparison is presented in the following chart. It would be difficult to draw any unambiguous conclusions from it. By definition, the Pentax designed for small sensors as a bit bigger pancake lens must be noticeably smaller and physically lighter than its full frame and full size rivals. In the photo below the tested lens is positioned next to other Limited devices, namely the smc DA 15 mm f/4.0 AL Limited and the smc FA 31 mm f/1.8 AL.

Pentax smc DA 21 mm f/3.2 AL Limited - Build quality

The Pentax smc DA 21 mm f/3.2 AL Limited is a small but stylishly designed „pancake” lens. Its housing and mount are made of metal. The only visible part made of plastics is situated in the rear part of the lens; it includes an inscription “Assembled in Vietnam”, which surrounds a rear element, 13 mm in diameter. The rear element’s size is so small that, like in the case of every “pancake”, it can make you feel anxious about the performance on the edge of the frame. The rear element moves with the whole optical system of the lens and, when you pass to the minimum focus, it hides several millimeters inside the housing.

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Pentax smc DA 21 mm f/3.2 AL Limited - Build quality

The housing itself is typical for new Limited series instruments – shapely, stylish, impossible to confuse with anything else. First you have a ring with fine ribbing on the left and on the right and a slivery inscription “PENTAX 21” in the middle. Then you see an immobile part of the housing on which there are depth of field markings by f/22, f/16, f/11, f/8 and f/4 aperture values.

The other part of the barrel consists, by and large, of a manual focus ring. You can find a distance scale, expressed in feet and meters, on it and it features a relatively narrow ribbing. The full turn of the ring takes a turn through less than 90 degrees. The ring works evenly and is well-damped so it would be difficult to complain here. Also carping about its small dimensions would be rather improper, taking into account the type of the lens.

The lens ends with a small inner tube with the front element system which extends while focusing. The front element is 22 mm in diameter and it is surrounded by a ring, threaded by two sides. The next part of the surroundings includes the name, parameters and a serial number of the lens along with a non-rotating filter thread, 49 mm in diameter.

When it comes to the inner construction we deal here with 8 elements positioned in 5 groups. Inside the lens we can also find an aperture with seven diaphragm blades which can be closed down to f/22.

Pentax smc DA 21 mm f/3.2 AL Limited - Build quality

In the accessory kit you get two caps. The rear one is made of plastics, the front one – of metal with inside velvet padding. You don’t put it directly on the lens but on a special hood with a rectangle-shaped window. The hood is attached to the lens using a bayonet mount. You also get a soft pouch in the box.

Pentax smc DA 21 mm f/3.2 AL Limited - Build quality