K-7 low light focus with fast lenses unreliable

Started Jul 6, 2009 | Discussions thread
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Ayoh
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K-7 low light focus with fast lenses unreliable
Jul 6, 2009

I have had a k-7 for a few days now and so far think it is fantastic. Feels very refined and well built and offers some major improvements over previous cameras. However I am not so sure about the low light focus performance especially with wide aperture lenses. In short it is all over the shop. I compared my k20d with the k-7 using FA 50mm, sigma 30mm 1.4, and 43mm limited lenses. The focus speed in low light, despite all the hype about major improvements, feels only marginally faster on the k-7. The difference is a lot larger though when the k-7's green assist light is switched on. However where the speeds are similar (not that the k20d was that bad) the accuracy is quite poor on th k-7. I calibrated my lenses on both cameras and when light is good there are no issues. Under very low light (~ 1/10s f1.4 iso3200) the k20d still focuses accurately. The k-7 however seems to be inconsistently back focusing or front focusing and seldom gets the focus spot on. The problem is especially evident with on the k-7 with the 50mm f1.4 and 30mm f1.4. The slower aperture 43mm f1.9 performs ok. None of the lenses exhibit the same problems on my k20d.

This has me somewhat worried as an unreliable camera is a lot more frustrating to use than a slow one, and the designers may have made the wrong trade-off. I have been unsing pentax DSLR's since 2003 and generally know what I am doing so there are no user error issues involved. I would be keen to hear other experiences which new k-7 owers have had and encourage other fussy owners to do some accuracy tests in case there is some firmware problem.

Aside from this one negative (although a big deal as far as I am concerned) I really think the camera is a fantastic complete package. ahh perfection eludes us again..

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