Was: "I use this lens with My k5. Same problem. Generally, I think the lens is a disaster, with the exception of 17- 24 mm. not only focus is bad. It has a terrible quality (going soft/blured) with high contrast conditions. One of the worst lenses I've ever owned."
I spent the day troubleshooting the lens based on all comments in this thread. I would like to moderate my rather categoric statement above. My conclusions are the following (all tests conducted at f/5.6 ISO 400 using both K5 and K20d):
- Results are the same on both bodies
- The autofocus sharpness at the 17-50 range is stunning. It is better than Sigma 18-50 2.5. It is not quite up to the Pentax DA 50-135/2.8 (at 50) lens but closer to that than to the Sigma lens. The sharpens at the 17-24 range is significantly better than my Pentax DA 12-24/4
- At 70mm, the focus is very unreliable (as escrowed by other posts). With manual focus, the sharpness is very good.
- Highlighted areas loose more detail and become a bit "blur" (edges "shine" into the surrounding areas and thus look unsharp) compared to the Sigma lens. With Aperture, I could compensate for that by reducing exposure (till details are back and blur is gone) combined with adjusting the luminance channel.
- The lens is not suitable for filming since there is not enough resistance in the focusing ring. I've been folding a lot with the lens and I constantly find my self mistakingly touching the focusing ring.
Test pictures at 70mm f5.6
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Plain_autofocus:
Autofocus with slight pressure on focus ring:
Manual focus