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05-01-2008, 03:16 PM   #1
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Is my K200D bad? Point of focus issues!

I need some help!


Here's the deal - For whatever reason, it seems like my point of focus on some shots is off. This is resulting in some very unsatisfying images, ones that I *shouldn't* be screwing up.
(Pentax K200D w/ Tamron LD Di 70-300mm)

Below is a perfect example -- You can look at the original resolution at Flickr.

The shot was *easy*. The bird was almost fearless, was taking his time. I had manual focus on, camera indicating when I was in focus.
Center focus point, bird's head looked sharp through viewfinder, etc. I was focusing on the bird's head.

When I open the file, though, I seem to have missed the focus!




I simply can't understand it.
There were no foreground objects. I was standing maybe 14 feet from the bird, standing up. It doesn't look like an issue of camera shake, but of comepletely missed focus in general, as you can pretty clearly see the focal point just ahead of the bird.


Am I just unlucky? or could something be wrong with the camera?
(I also posted this in the Arstechnica A/V forum - looking for some smarts, as I seem to lack them!)

05-01-2008, 03:32 PM   #2
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Do you have other lenses to test with? Its certainly possible that you have a problem either with the body or lens. One missed shot doesn't really indicate a problem, but if its consistent and the same direction every time its worth testing more rigorously.
05-01-2008, 04:04 PM   #3
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What focus point where you on? The head is of center, so did you move the camera aim or used another sensor then center one? The focus indicator in manual use is quite sensitive, so it is easy to go slightly past the indicated focus point. Try with the autofocus instead, so you'll know if it is the camera/lens combination. There is also the possibility of sensor not being exactly positioned where the red indicator in the viewfinder shows. You should try to download a focus target and check with it.
05-01-2008, 04:12 PM   #4
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Thanks for the suggestions -- I may need to try with autofocusing.

A helpful guy at Ars posted a link to an autofocus test -- I printed out the pattern, tested it out and ran the test -- very slight backfocus with this lens but nothing serious.

I was on the middle focus point .


Of about 15 shots of this bird, 12 or so have this problem, so maybe it's me ><
Bah!

Oh well, thanks for the help

05-01-2008, 04:15 PM   #5
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Have you tried adjusting the diopter? you may have it off by a click or two, where it will LOOK in focus in the viewfinder, but isn't really focused, happened to me once..
05-01-2008, 07:15 PM   #6
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How do you check AF point alignment? I think i have the same problem with K100D super.
05-02-2008, 06:41 AM   #7
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Your bird head looks front focused. I suggest you should check if this FF problem is consistent or not before coming up to any conclusion.

AF sometimes does fail and inconsistency does occur. As long as the failure rate is not too high and that the inconsistency is not too large, I think it is just acceptable.
05-03-2008, 03:12 PM   #8
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Rice, cputeq was using manual focus, not AF. My initial thought coincided with Stratman's; it's not unheard of to knock the diopter adjustment off, leading to problematic manual focus.

Another thought was that, at fairly close range, a 200mm FL (even at f/8) will have a fairly narrow depth of field. If one is shooting handheld, small unsteadinesses of the standing or kneeling human body (I refer to whole body movement, not hand shake) on the z-axis (back and forth motion) often occur, and may affect the focus plane if they happen after focus is locked but before the shutter is released.

The SR system can't compensate for nearly as much z-axis movement as the photographer's body can generate while trying to keep its balance. In my experience , such unsteadiness can significantly shift the point/plane of actual focus. (That's why we love tripods, when we can use them!) Just a possibility to consider when out shooting.

05-03-2008, 03:43 PM   #9
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QuoteOriginally posted by jdg Quote
How do you check AF point alignment? I think i have the same problem with K100D super.
You put your camera to AF-C, you select one AF sensor and you aim at a wall wit something for the camera to focus on (a brick wall is great), then, with the shutter button at half pres and watching through the viewfinder, you slowly push a pencil (or something similar) toward the selected focus point and you'll see when the camera start shifting focus. It should be very close to the intended focus sensor you selected.
05-03-2008, 05:03 PM   #10
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QuoteOriginally posted by flyer Quote
You put your camera to AF-C, you select one AF sensor and you aim at a wall wit something for the camera to focus on (a brick wall is great), then, with the shutter button at half pres and watching through the viewfinder, you slowly push a pencil (or something similar) toward the selected focus point and you'll see when the camera start shifting focus. It should be very close to the intended focus sensor you selected.
Just tested my k100ds AF points and it's a little bit off to the right side.
05-05-2008, 09:05 AM   #11
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Yah, any serious focus testing needs to be carried out on a tripod and preferably with a release.
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