Pentax DA* 60-250mm F/4 SDM Review

Pentax designed a new optical formula for the DA* 60-250mm F/4 SDM to match the ultimate resolution at the time and provide room for higher-resolutions in the future. Back in 2008, Pentax DSLR just jumped from 10 to 15 MP. The result is a lens that produces legendary results with contemporary cameras and remains reasonable on modern 26 MP DSLR that capture 70% more resolution!

It is significantly easier to produce a telephoto lens than a wide-angle one without distortion. Unsurprisingly, the DA* 60-250mm F/4 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.

Optically, this constant-aperture telephoto zoom offers a similar yet slightly superior performance than the DA* 50-135mm F/2.8 SDM launched one year earlier. Much performance characteristics are comparable but contrast notably improved with the DA* 60-250mm F/4 SDM. This lens is extremely resistant to flare and chromatic aberrations. Purple fringing is also a rare occurrence.

Pentax 60-250mm F/4

Pentax DA* 60-250mm F/4 SDM Sharpness

Excellent sharpness is achievable with this lens when stopped down sufficiently. There is much less variation in sharpness in relation to focal-length than with other DA* lenses, although output is slightly better towards the longer half of the focal-range. Near the wide end, there is generalized softness from edge-to-edge which improves by stopping down. Around F/6.7, everything is acceptably sharp and at F/8 the entire image becomes completely sharp.

Towards the middle of the range, there is some definite softness across the frame yet it is minimal near the center. Closing the aperture to F/4.5 makes the center sharp and improves corners. Only a half-stop more at F/5.6 does the entire image become sharp from edge-to-edge. Stopping down further to F/6.7 and F/8 incrementally sharpens the image. Diffraction starts taking effect around F/13.

The extreme telephoto focal-length of this lens shows similar qualities than the middle. The entire image has a slight softness at F/4 and this improves at F/4.5 with a greater improvement near the center. F/5.6, just one stop down from wide-open on this lens, captures sharp images. To maximize corner-to-corner sharpness, it is necessary to stop down to F/6.7.

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 clearly show the progression from generalized softness to fully image sharpness according to aperture. The good news is that images can be sharp from corner to corner when stopped down 1.5 stops from wide open. There is a slight bias towards the long end of the zoom yet this difference has little impact on typical print sizes.

Autofocus Performance

This is a repetition of the analysis of first-generation SDM motors encountered in the DA* 16-50mm F/2.8 SDM and DA* 50-135mm F/2.8 SDM. Only launched a year later, this lens does not show any reliability improvement with its SDM motor. It has a tendency to fail which is why the backup screw-drive autofocus system saved the series.

Autofocus speed of this lens is highly variable. It can focus quite quickly when the SDM motor responds well but this is not always the case. The screw-drive system is much more reliable. It is a little slower but never stalls completely. This lens can handle tracking subjects with medium speed.