Pentax DA* 16-50mm f/2.8ED AL [IF] SDM Lens Review

Pentax DA* 16-50mm f/2.8ED AL [IF] SDM Performance

At 16mm and f/2.8, sharpness in the centre of the frame is already outstanding. Unfortunately the performance of the lens towards the edges of the frame isn't quite as good at maximum aperture, only achieving fairly good levels of clarity. Stopping down improves performance across the frame, with peak sharpness being achieved between f/5.6 and f/8. Here sharpness is outstanding in the centre of the frame and very good towards the edges.

Zooming to 28mm, results in reduced sharpness levels in the centre of the frame at maximum aperture, but performance towards the edges of the frame remains similar to 16mm. Again, stopping down to f/5.6 results in the best performance across the frame, with outstanding sharpness in the centre and excellent clarity towards the edges of the frame.

Finally at 50mm. Overall sharpness takes a hit at maximum aperture, with good levels of sharpness being achieved in the centre of the frame, but performance towards the edges of the frame can only be considered fair. Stopping down to f/8 results in outstanding sharpness across the frame at this focal length.

MTF@16mm

MTF@28mm

MTF@50mm

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 brought under better control, the more the lens is zoomed in. Fringing is most prominent at 16mm and f/2.8, where it exceeds 1.25 pixel widths towards the edges of the frame. This level of fringing may become apparent in harsh crops from the edges of the frame, or in large prints along high contrast edges.

CA@16mm

CA@28mm

CA@50mm

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 fairly typical for a lens of this range and maximum aperture. At 16mm the corners of the frame are 1.62 stops darker than the image centre and at 50mm the corners are 1.1 stops darker. Visually uniform illumination is achieved with the lens stopped down to f/5.6 or beyond throughout the zoom range.

Distortion is fairly noticeable at 16mm. Easing as the lens is zoomed in. Imatest detected 4.11% barrel distortion at 16mm, which is replaced by 0.373% pincushion distortion at 50mm. The distortion pattern is uniform across the frame, which should make it relatively easy to apply corrections in image editing software afterwards if straight lines are paramount.

During testing, this lens proved itself quite resistant to flare and contrast levels are retained well, even when shooting into the light. The petal-shaped hood does a decent job of shading the lens from extraneous light that may cause issues.

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