Pentax HD PENTAX-DA 40mm f/2.8 Limited Lens Review

HD PENTAX-DA 40mm f/2.8 Limited Performance

At maximum aperture, sharpness in the centre of the frame is already excellent, and the clarity recorded towards the edges of the frame falls just short of good levels at this aperture. Stopping down improves sharpness across the frame, with peak performance being realised at f/8. Here sharpness is outstanding in the centre and excellent towards the edges of the frame.

40mm @ MTF

How to read our charts The blue column represents readings from the centre of the picture frame at the various apertures and the green is from the edges. Averaging them out gives the red weighted column. The scale on the left side is an indication of actual image resolution. The taller the column, the better the lens performance. Simple. For this review, the lens was tested on a Pentax K-5 IIs using Imatest.

Chromatic aberrations are extremely well controlled, with remaining well below a quarter of a pixel width at nearly all apertures.

CA @ 40mm

How to read our charts Chromatic aberration is the lens' inability to focus on the sensor or film all colours of visible light at the same point. Severe chromatic aberration gives a noticeable fringing or a halo effect around sharp edges within the picture. It can be cured in software. Apochromatic lenses have special lens elements (aspheric, extra-low dispersion etc) to minimize the problem, hence they usually cost more. For this review, the lens was tested on a Pentax K-5 IIs using Imatest.

Falloff of illumination is well controlled for a lens with an f/2.8 maximum aperture. At f/2.8 the corners of the frame are 1.03 stops darker than the image centre and visually uniform illumination is achieved with the lens stopped down to f/5.6 or beyond.

Only a minute amount of barrel distortion is present in images taken with this lens. Imatest detected 0.538% barrel distortion, which will be very hard to spot, unless straight lines very near the edges of the frame run absolutely parallel with the frame border. The distortion pattern is uniform across the frame, so if you require absolutely straight lines, this low level of distortion should be relatively easy to correct.

During testing, this lens proved itself very resistant to flare and contrast levels remain good, even when shooting into the light. The dinky little lens hood that is supplied with the lens does a great job of shielding the lens from extraneous light, as well as from bumps and scrapes.

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