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Lens review

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR

8 February 2014
Arkadiusz Olech

3. Build quality

As it is often the case with a Pentax, it is difficult to find a direct competitor, directly comparable to it, due to untypical parameters. A similar range of angles of view is provided by the mirrorless Samsung NX 20-50 mm f/3.5-5.6 ED so we included in our comparison chart. We complemented it with the full frame Tokina 19-35 mm and the fast Sigma A 18-35 mm f/1.8, designed for smaller APS-C/DX sensors.

In the photo below the tested Pentax 20–40 mm is positioned between the Zeiss Macro-Planar 2/50 and the Sigma A 35 mm f/1.4.

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR - Build quality


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The Pentax 20–40 mm starts with a metal mount, surrounded by a red, rubber gasket which ensures the joint between a camera and the lens is sealed. Inside the mount you can find contacts and a thin, black bottom with a 15-mm hole through which you see a rear element. On the bottom there is an inscription “ASSEMBLED IN VIETNAM”. The rear element changes its position, being on the same level as the mount at 20 mm and hiding about 2.5 cm deep inside when you pass to 40 mm focal length.

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR - Build quality


The proper body of the lens is made of metal; it starts with an immobile ring with an inscription “2.8-4/20-40” and is surrounded by fine ribbing from both sides. A zoom ring is the next part – it is 17 mm wide, with comfortable protuberances and ribs. Its work is beyond reproach: even, smooth and well-damped.

Further on, you meet a depth of field scale with markings for f/32, f/22, f/16, f/8 and f/4. The presence of the f/32 marking means that the scale concerns 40 mm focal length because only at that length such an aperture value is available.

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR - Build quality


Above the scale you get a manual focus ring, 11 mm wide, covered by fine ribs and adorned by a red stripe. The ring moves both in the MF and AF mode and its work is beyond reproach. Still you can have one reservation – the working range is too narrow. In order to run through the whole distance scale you need a turn of less than 70 degrees. It is really not enough.

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR - Build quality


The front element system is set on a movable tube which position changes along with the change of the focal length and/or focus. It is hidden the deepest at 32 mm with the focus set at infinity and then its dimensions increase to the maximum when you pass to 20 mm focal length, with the focus set at 0.28 of a meter.

The front element is slightly convex, 40 mm in diameter. It is surrounded by an inscription with the name and the parameters of the lens with a non-rotating filter thread, 55 mm in diameter. Unfortunately the same filter thread is also used to attach a small hood which, in turn, serves also as a cap adapter ring. When you screw the filter in, you can use neither a hood nor a cap in order to e.g. protect the lens and the filter. I have to say such a solution is rather ill-considered…

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR - Build quality


The lens consists of 9 elements positioned in 8 groups. One element is aspherical, one is made of extra-low dispersion glass (ED) and another one – of a different kind of glass with exceptionally low dispersion. Inside you can also find a circular aperture with nine blades which can be closed down to f/22 at 20 mm and to f/32 at 40 mm focal length. The Pentax company additionally boasts of employing new, efficient HD coatings.

The buyers get both caps and a tiny hood in the box.

Pentax HD DA 20-40 mm f/2.8-4.0 ED Limited DC WR - Build quality