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03-19-2013, 02:56 PM   #1
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K5 with Fast lenses : Help required

I upgraded from K200D to K5 a month back. So far I have 4 lenses –Pentax 18-250mm, Pentax DA 35mm f2.4, Pentax A 50mm f1.7 and the Sigma 50-150mm f2.8 acquired 2 weeks back. I would like to point out that I am not a fan of either using flash or LV until and unless it is a ‘Do or die’ situation.
I am having a ‘not so good time’ trying to get the autofocus on the K5 to work accurately. I am not sure if it is a something wrong which I am doing (which is easily fixed), is this a problem with the K5, a problem with one or more lenses, or I am simply trying to push the tools to their limit which is causing this. The K200 was unable to autofocus in most of these cases so I am happy but because most of the times the focus is off, it is not of much help. So far most of my testing has been indoors in well-lit tungsten lighted hotel room but I have had the privilege to take the camera out on two weekends, once with the 18-250mm and 35 mm and the other time with the Sigma and the 35mm.
I was facing some initial challenges with the autofocus but once I upgraded the firmware to 1.14 it seemed to fix the AF to a large extent, or maybe it is just my perception.
The Pentax 18-250mm seems to be working fine in most cases and the focus seems to be spot on, maybe I feel so because of the large F number. This has been my workhorse lens for most of the 5 years I have used it with the K200 and my favorite walkabout lens.
I have not yet tested the A 50mm f1.7 as it is a manual lens so keeping it out of the equation as of now.
The other two lenses are the ones which I seem to have issues with
First - The 35mm f2.4 (when shooting wide open)
I mostly shoot it wide open, I know it is a bit soft at that setting but with the K200 I needed the additional light. With the K200 I did notice at times that the subject would be front focusing if not lit properly, eg. the subject has the sky in the background, etc but having the flash on, took care of that. Also, if the distance from the subject was large, then again it would be out of focus by a large magnitude. But in most cases (approx. 90%) it stood ground. With the K5, it is a similar experience but maybe much lesser accurate focus shots. Did not have LV with K200 so cannot comment but with the K5 using the LV, the focus is spot on.

Now for the Sigma (when shooting wide open most times which started all of this)
Before the K5 firmware upgrade, the focus was all over the place. Post the firmware upgrade, I was able to focus it consistently by dialing in -10 on the AV Micro Adjust. It was still not a 100% there but almost. Following the advice of some ‘Gurus’ on the forum consistent with elsewhere on the net, I sent my K5 and the Sigma lens to Sigma for recalibration. Got it back last evening and still had to dial in -10 to get it nearly there. Still not there 100%. Not a major change from before. The focus via LV is perfect and spot on (when it works).
https://picasaweb.google.com/104645425869793713046/ScrapbookPhotos#5857227846587287570 - using view finder
https://picasaweb.google.com/104645425869793713046/ScrapbookPhotos#5857227846891060738 - using LV
So not sure if it is a lens issue or a K5 issue.
Major observations
• Overhead lighting seems to force the AF to front focus considerably. So far have tested it only with tungsten lighting both at home and at a concert.
https://picasaweb.google.com/104645425869793713046/ScrapbookPhotos#5857226934049031426
https://picasaweb.google.com/104645425869793713046/ScrapbookPhotos#5857226971362355378
• When shooting up close, the focus is acceptable (not 100% accurate though) but as the distance from the subject increases, it gets worse.
• I noticed yesterday that when shooting a subject lit by tungsten at 150 mm the focus was fine but the same subject when shot at 50mm was front focusing substantially
• Bright light sources seem to throw the focus off. Also, shooting a glass covered subject, eg.a clock there was a significant back focus.
https://picasaweb.google.com/104645425869793713046/ScrapbookPhotos#5857226930593967346

• Backit subjects cause front focusing substantially.
https://picasaweb.google.com/104645425869793713046/ScrapbookPhotos#5857226930387686098

I am not sure if the size of the AF points is a problem but I am aware of that and can work around it. Or if the lack of 2.8 AF sensors in the K5 are causing this which has been rectified in the K5II. Or if low light is a problem but the 18-250 works fine in the same light so a faster lens should work better.

I desperately need help. This is driving me nuts. I am wondering if I made the mistake of buying into the K5 (rather than the K5II (additional 40%) or jumping the gun to Canon 7D (additional 50-60%)).

I can post sample pictures for whichever point you need data on.


Last edited by skamalpreet; 03-19-2013 at 06:26 PM.
03-19-2013, 03:51 PM   #2
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QuoteOriginally posted by skamalpreet Quote
if low light is a problem but the 18-250 works fine in the same light
There are so many [too many?] variables in this whole problem to make any conclusive statement about what is going on - no FF when close, FF when distant, then the reverse with another lens, bright light, backlighting, overhead lighting, glass ??, tungsten causing FF. Etc etc.

If the 18-250 works OK, it does suggest at a minimum that your lenses are making a considerable contribution to your problems. There may also be issues about your AF and metering settings which are making their own contribution. You may need to review those settings.

Last edited by rawr; 03-19-2013 at 03:57 PM.
03-19-2013, 04:34 PM   #3
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From my limited experience, your A50/1.7 might be very useful here. With F series and newer lenses, the lens provides some information to the camera about what distance is in focus. Without this information, the camera simply has to use its phase detect sensors to determine focus. So using any manual focus lens can help you dial in the accuracy of the AF calibration, especially a fast f/1.7 lens.

I'm assuming that you're using only center point autofocus. If not, the camera could just be choosing the wrong point to focus on. Also, that you're using the green hexagon and not the red square to determine when focus is achieved.

I find it interesting that the 35/2.4 would have worse performance the further away the subject is, and that the zoom would vary between focal lengths. Have you had an opportunity to test this in sunlight?

Finally, I'll commend your observation that the 35mm lens is a lot faster than the 18-250, and I'll add that the K-5 has much more resolution than the K-200. Both of these issues make any AF failures much more apparent.

If I were to narrow down the issue, I'd set up a repeatable test. For example, mount the camera on a tripod (or rest it in a specific location on a stable surface) and test the AF on a high contrast subject that won't move, such as a bookshelf or a building across the street. This way, you can see if there are patterns to the problems, which can help you fix them.

Best of luck!
03-19-2013, 05:07 PM   #4
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QuoteOriginally posted by JonPB Quote
I'm assuming that you're using only center point autofocus. If not, the camera could just be choosing the wrong point to focus on. Also, that you're using the green hexagon and not the red square to determine when focus is achieved.
Affirmative to both of the above

03-19-2013, 05:10 PM   #5
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QuoteOriginally posted by rawr Quote
There are so many [too many?] variables in this whole problem to make any conclusive statement about what is going on - no FF when close, FF when distant, then the reverse with another lens, bright light, backlighting, overhead lighting, glass ??, tungsten causing FF. Etc etc.

If the 18-250 works OK, it does suggest at a minimum that your lenses are making a considerable contribution to your problems. There may also be issues about your AF and metering settings which are making their own contribution. You may need to review those settings.
I tried to explain my problems at length here. I have been shooting for 5 years using Pentax but never faced these issues before. Hence the reason I am baffled.
03-19-2013, 07:55 PM   #6
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One item in your detailed explanation that sticks out for me is when you said you shot a subject with live view and it was in focus, but the same shot through the viewfinder is not in focus. If you setup and subject were exactly the same for both shots, then that points to a camera AF problem. If a shot is in focus with live view the lens is usually fine.

As was eluded to in a couple of the responses above, you need to set up a controlled test. You can't be shooting different subjects at different distances in different lighting conditions and come to any kind of conclusion.

Not to confuse the issue any more than it already is - I have just sent my second K-5 to Pentax repair for AF issues. With both my K-5's they both performed perfectly when they were new. Then after a few months use, I noticed my lenses all of a sudden needed a lot of AF adjustment. It drove me nuts for a couple days until I did a controlled test to prove it to myself that it was the camera AF and not my lenses......or not myself going nuts. In both instances the work order stated that the AF on the camera needed adjusted to bring it back to factory specs - that the camera itself was back focusing. When I got the first one back, it was right on with all my lenses just like when it was new. The second one is on its way back to me right now.
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