Pentax SMC-DA 21mm f/3.2 AL Limited Interchangeable Lens Review

Pentax have announced this new, compact prime lens for use on their digital SLR cameras. Slim and lightweight, we take a look at this aluminium-housed optic.

Specifications

• Model smc-DA 21mm f/3.2 AL Limited
• Focal length 21mm (32mm equivalent)
• Max aperture f/3.2
  Min aperture f/22
• Construction 8/5 elements/groups
• Angle of view 68deg
• Closest focus 20cm
• Mag ratio 1:5.9
• Filter size 49mm
• Dimensions 25x63mm
• Weight 0.26kg
• Price (SRP) £419.99

Build and handling
The body of this tiny 21mm optic is made from aluminium and is well engineered. The whole lens, when mounted on the camera, only protrudes some 25mm and this is only extended barely 5mm by focusing to the closest point, a commendable 20cm. The lens is supplied with a bayonet fit hood that fits inside the lens cap, again made from aluminium, and slides neatly over the front of the lens with the hood in place. The hood is, in fact, more of a shield than conventional hoods and this must be removed to use 49mm filters or systems. It has small ‘wings’ on the bayonet to extend past the filter thread and cannot therefore be used with filters in place.

The only control on the lens is the manual focus ring, a narrow but usable affair with a milled grip behind which is a cut-out with the distance scale marked in metres and feet. It sports a full, conventional, depth-of-field scale and all of the markings are etched into the metal.

The focus ring is lightly torqued and can be used to over-ride the auto setting without recourse to switching the AF off and this can be achieved with the use of a single digit. The overall impression of the lens is that it is solid and built to last. Supplied in a drawstring leatherette pouch with lens and body caps, the whole thing will fit easily in a pocket or handbag.

Optical quality
The optical quality of this lens is commendable for such a compact design and is relatively consistent throughout the aperture range as far as resolution is concerned. There is a gently improving slope towards the optimum, which is reached at around f/11 and there is no fall-off in quality towards the edges. In fact, the edges measure fractionally better than the centre!

The control of aberrations such as chromatic aberration is good for the most part, although there is some visible evidence as the aperture reaches higher values, especially at the edges and corners of the frame.
Surprisingly for a prime lens, there is some evidence of barrel distortion and although it is not too severe and easily corrected in post processing, it is visible with straight lines near the edges of the frame.

The lens produces neutral colours and the control of flare and ghosting is good, giving decent contrast to images.

Click on each comparison test photo below to view full size versions

Pentax 21mm at f/8

Pentax 21mm at f/3.2

Verdict
Mechanically well engineered and giving good resolution results across the frame and aperture range, this lens makes a nice, but not exceptional wide angle addition to the kit with virtually no space or weight penalty. A pricey headline figure, but expect to find it well discounted.

In summary, the positive points of the SMC Pentax DA 21mm f/3.2 AL Limited are:
Compact in the extreme
Good resolution across the frame
Good build quality gives confidence in longevity

The negative points are:
Some barrel distortion
Some CA when stopped well down.
Price

Check the latest price for the SMC Pentax DA 21mm f/3.2 AL here

Test by Ian Andrews www.wildaboutkent.com