HD PENTAX-DA 15mm f/4 ED AL Limited Lens Review

Pentax HD PENTAX-DA 15mm f/4 ED AL Limited Performance

At maximum aperture, sharpness in the centre of the frame is already excellent, although clarity towards the edges of the frame falls behind somewhat. Stopping down the aperture improves sharpness across the frame, with sharpness in the centre reaching outstanding levels between f/5.6 and f/8. Performance towards the edges of the frame never quite catches up to that of the centre, and is fairly good between f/5.6 and f/16.

MTF @ 15mm

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 very well controlled for an ultra wide angle lens, with fringing remaining around half a pixel width at all apertures.

CA @ 15mm

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 reasonably controlled for a wide angle lens. At f/4 the corners of the frame are 1.43 stops darker than the image centre and visually uniform illumination is achieved with the lens stopped down to f/8 or beyond.

Distortion is also well controlled for a lens of this type. Imatest detected 1.23% barrel distortion, which isn't much at all. Unfortunately the distortion pattern isn't uniform across the frame, having a very slight wave to it. This may be an issue if you require absolutely straight lines, as it will make applying corrections in image editing software afterwards more difficult.

During testing, this lens proved itself resistant to flare and contrast levels remain good, even when shooting into the light. The pop out hood built into the lens is petal shaped and does a great job of shielding the lens from extraneous light.

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