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12-30-2010, 05:52 PM   #1
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New K5/lens issue?

My brand new (bought Dec. 27th locally) K5's AF doesn't play well with my 77 Ltd and I wonder if there's something I'm missing. I shot some focus charts and they don't show any real focus issues. But I've noticed significant focus inconsistencies with this lens - today some pictures were back-focused (focused on a retaining wall, the street beyond was in focus), some front focused (focused on a tree, the road in front of the tree was in focus, another one I focused on clouds and the road right in front of the car was in focus) and some right on (though the sign picture was at the edge of being in focus).

I have one lens that front focuses (DA 35 macro) but was easily corrected and is now accurate. The DA*300 seems very, very close if not bang-on. I haven't used the rest of my AF lenses enough to get a good feel for them - other than the fact that they all looked OK when shooting focus charts (not necessarily definitive).

Has anyone else experienced this inconsistency with any lens? Is there something I can do that would help make it more accurate?

12-30-2010, 05:59 PM   #2
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Yes, I have that problem with my DA 16-45. Usually shooting at an angle to something and almost never straight on. Sometimes it occurs with my Sigma 150-500, but not often. The K-5 DOES NOT like my Helios 44 but does like my Industar. I am confused as well.....
12-30-2010, 09:39 PM   #3
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Aparently the AF sensors on the K5 are larger than the indicated area in the viewfinder. Is is possible that it locked focus on something else near the area of interest? Thus far, the only AF issues I've had have been in very low light (in at least one case, it was too dark to manually focus either).
12-31-2010, 11:16 AM   #4
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I don't think it's the fact the sensor is bigger than the indicator with the two front focus shots. Both times where it focused was in the lower third of the frame. I thought it might not be focusing to infinity for some reason but that's not so - one of my favorite shots from the day was a distant shot and everything was in focus. It might have been a factor with the back focused shots as both were fairly busy scenes and the focus subject wasn't that big. Anyone else have a suggestion or possible cause or problems with a particular lens?

12-31-2010, 04:04 PM   #5
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Some Things to Check

QuoteOriginally posted by mtngal Quote
My brand new (bought Dec. 27th locally) K5's AF doesn't play well with my 77 Ltd and I wonder if there's something I'm missing. I shot some focus charts and they don't show any real focus issues. But I've noticed significant focus inconsistencies with this lens - today some pictures were back-focused (focused on a retaining wall, the street beyond was in focus), some front focused (focused on a tree, the road in front of the tree was in focus, another one I focused on clouds and the road right in front of the car was in focus) and some right on (though the sign picture was at the edge of being in focus).

I have one lens that front focuses (DA 35 macro) but was easily corrected and is now accurate. The DA*300 seems very, very close if not bang-on. I haven't used the rest of my AF lenses enough to get a good feel for them - other than the fact that they all looked OK when shooting focus charts (not necessarily definitive).

Has anyone else experienced this inconsistency with any lens? Is there something I can do that would help make it more accurate?
Check your focus point selections and other AF setup options.

If you are letting the camera choose the points it might not be choosing what you expect.

In addition, if you are in AF-C the camera might be selecting something to lock on before you are ready.

Lastly, check if you have the camera set to fps or focus priority. In fps it will take an image even if nothing is in focus.

Ignore all of this if you already know or have tried all of these things.

BTW, my 77 seems to work ok so far, but I do not yet have much time with it and my K5.

Ray
12-31-2010, 05:07 PM   #6
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There would seem to be a low (artificial?) light AF issue with the K-5 where a firmware fix is expected soonish: https://www.pentaxforums.com/forums/pentax-k-5-forum/126234-who-cares-bad-aut...ten-light.html. I too have been a bit puzzled with K-5 AF at times, but I think I wait for the FW update and start to worry about it properly only, if there still seems to be a problem after that :-)
12-31-2010, 06:25 PM   #7
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I know it's not the artificial light issue as these pictures were all taken outside. I have an I-don't-know-what-I'm-talking-about/uneducated theory about the situation, and am waiting to see what type of fix Pentax comes up with about the problem. That's a whole different subject.

Ray - I hate letting the camera choose the focus point, 9 times out of 10 it will choose the wrong thing. So the first thing I did when I got the camera was change to center point and I haven't had a reason to change to other points yet. Hmmm - didn't think about AF-C. I don't think it was set that way as I usually leave it on AF-S, but I HAD used AF-C the day before and might not have changed it back until after I took the pictures in question. Focus priority or fps setting? Forgot someone mentioned that it was a new option on the K5, I haven't even thought about that - it's set for whatever the default is, better dig out the book and check to see what and where to find that. Thanks very much for bringing that up! Gives me an excuse to both read the owners manual and experiment more. Is there anything else I might have missed?

I did some more casual shooting with the K5 and the DA*50-135 and a few with the 10-17. The 50-135 not only is consistent but right-on, a pleasant change since it back focused a bit with my previous camera.
01-07-2011, 06:40 PM   #8
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Update on my K5/77 problem. I first spent a lunchtime several days ago outside walking around and taking random shots with the 77 on the K5. I took 47 shots. 40 were focused correctly. 5 either had excuses or were very close. 2 were way off and had no reason for being as badly focused as they were - one was more or less a close-up where the subject almost completely filled the frame. I took a second picture right after and it was correctly focused.

The next day I took the K5 with the DA 35 macro and the K7 with the 77 on it (I know, different animals). I took 34 pictures with the K7 and all of them were either correctly focused or had excuses, as were all the K5/ DA 35 macro pictures.

Which brings up the question - what is an acceptable rate of AF failure? I've been trying to convince myself to not be disappointed with the results, it's not like I'm a pro and depending on faultless performance for my living. Or shooting sports where you don't have time to chimp. And 2 bad out of 47 is a 95% success rate, it's not horrible. The only problem with this logic is that I've become very used to either perfectly focused shots or ones where it's obvious what the camera focused on.

01-07-2011, 09:02 PM   #9
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My 77 works fine after I entered a +6 correction for back focusing

David
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