Pentax DA* 50-135mm F/2.8 SDM Review

Pentax designed a new optical formula for the DA* 50-135mm F/2.8 SDM to match the ultimate resolution at the time and provide room for higher-resolutions in the future. Back in 2007, the highest resolution Pentax DSLR offers 10 MP, while competitors offers 12 megapixels. The result is a lens that produces legendary results with contemporary cameras and remains reasonable on modern 26 MP DSLR that capture 160% more resolution!

It is significantly easier to produce a telephoto lens than a wide-angle one without distortion. Unsurprisingly, the DA* 50-135mm F/2.8 SDM shows virtually no discernible distortion at any focal-length. Also completely absent from images at any aperture is vignetting. The geometry of this lens is exemplary.

This constant-aperture telephoto zoom is also highly resistant to flare and chromatic aberrations. There can be some slight purple fringing right on an edge of extreme contrast yet camera firmware removes this very effectively these days, so it is unlikely to appear in photos. This lens produce fairly good contrast. Its output is not as crisp as that from lenses with modern nano-crystal coatings.

Pentax 50-135mm F/2.8

Pentax DA* 50-135mm F/2.8 SDM Sharpness

Sharpness from this lens varies greatly along edges yet the center is always sharp. Towards the wide-end of the zoom, images are very sharp in the center, even fully open. Stopping down just a half-stop makes the center razor sharp until the point where diffraction appears, around F/9.5. The review until of this lens is slightly decentered which make upper corners softer than lower ones. Wide-open, all corners appear soft at wide-angle. While upper corners took all the way to F/8 to sharpen, lower corners became fairly sharp at F/4. They improved at F/6.7 but never become perfectly sharp.

Around middle focal-lengths, the center of images captured by the Pentax DA* 50-135mm F/2.8 SDM is razor sharp even wide-open. Stopping down maintains this perfect sharpness until F/9.5. Corners appear soft at F/2.8 but they sharpen up quickly. F/4 produces very usable corners Closing the aperture more to F/5.6 results in very sharp corners all around.

The long-end of this zoom shows similar results to its wide end. The center is fairly sharp wide-open then and becomes very sharp at F/3.5 and beyond. Corners are all soft wide-open which improves slightly with every fractional aperture beyond that. Unlike the wide-end, corners at this long focal-length never become sufficiently sharp to make very large prints.

What is shown below are 5 crops taken from a photograph, repeatedly captured for each combination of focal-length and aperture. The smaller pieces are cropped from the extreme corners of the image, while the middle wide crop comes from the center of the image. Select an aperture in a row for a desired focal-length to see the crops from the corresponding image. When judging quality, keep in mind that these crops come from a 26 MP image which is normally used to print an image up to 30x20". On a computer display, these may appear much larger which magnifies image defects.

Upper Left

Upper Right

Center

Lower Left

Lower Right

The above interactive crops really show the difference between extreme corners to the center and how it varies according to aperture. Stopped down at F/5.6 and beyond, this lens produces sufficiently detailed images. There is clearly a loss of image-quality near corners that was not anticipated in 2007. For typical print-sizes though, the difference is much harder to note than in these 100% crops.

Autofocus Performance

The struggles of SDM motors are real. The autofocus speed of this lens is all-over-the-place. Many times, it focuses quickly and quietly, particularly with more distant subjects. It is typical to get AF lock in under a half second. Other times, one can see focus move slowly towards its subject. The screw-drive motor proves a much more consistent experience. It is slower and, on average, faster than SDM.

While this lens can be used with success with moving subject, it is too inconsistent to recommend for sports other types of photography where timing is essential. For the occasional moving subject or street photography where one often prefocuses at a certain distance, then it is capable. For portraits, subject moves yet generally very little and so this lens can manage to track sufficiently well.