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08-27-2011, 05:36 PM   #1
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Bad focus on K-10D.

My K-10D has always seriously back-focused. Using my 80-200 Tokina f2.8 at 2.8, for say, portrait work, the eyes seem sharp and clear in the finder, and red focus light confirms. When pics are in lightroom, for example, the eyes are noticably soft, and the ears are perfect.
I installed the debug setup in my firmware, and sometimes the corrections seem to work, but with the 16-45, even at f8, focus is often soft. Manual focus with a tripod gives the same results. I'm doing some tabletop product photography at the moment, using both the 16-45 and an old Pentax 50mm f1.7 AF lens. The focus correction is currently set on + 230 nanometres, but there's still a bit of back focus. I've been trying to guess the settings, and doing a crude focus bracket, so some of the shots are turning out fine. This is a bit haphazard though.
What's going on here? Obviously the focusing is done in the finder, and the finder assumes it knows where the chip is. Could this be a by-product of in- camera dust removal? Why does no-one else seem to have this problem? If theres no problem, why is the back focus (secretly) adjustable?
If anybody can enlighten my, I'd be most grateful.

Jan.

08-27-2011, 11:33 PM   #2
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Do you use any sort of split screen?
08-28-2011, 09:03 AM   #3
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QuoteOriginally posted by flashcactus Quote
My K-10D has always seriously back-focused. Using my 80-200 Tokina f2.8 at 2.8, for say, portrait work, the eyes seem sharp and clear in the finder, and red focus light confirms. When pics are in lightroom, for example, the eyes are noticably soft, and the ears are perfect.
The viewfinder shows too much DOF with fast lenses, causing things to look in focus that really aren't. See lots of other threads on the difficulties of manually focusing with fast lenses.

The red light is not the focus confirm - it is merely telling you which focus point is active. It can indeed light up before the subject is in focus. The green hexagon is what you should be waiting for. But even that is not foolproof. All it tells you is that something within range of the focus sensor is in focus - or close enough to in focus, anyhow. Unless you are doing a closeup of just the eyes, nose, and mouth, the focus sensors are not narrow enough to allow you to be sure where on the face focus is being achieved.

QuoteQuote:
Could this be a by-product of in- camera dust removal? Why does no-one else seem to have this problem?
??? I believe you'll find at least a hundred existing thrads where people discuss their focus difficulties. Probably several hundred. Not all, or even most, are describing actual camera problems - often, it is things like failing to realize the viewfinder lies about DOF or that the focus sensos are larger than the red viewfinder indicators. You should definely read up on those theads for advice on conducting good focus tests and the things that simply cannot be solved through the debug menu.
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