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05-08-2010, 04:23 AM   #1
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K7 - Bad Auto Focus or what?

I'm not happy with the auto focus on my K7.
As an example for this post, I took two shots of the wooden decorative top of my patio umbrella. The K7 was mounted on a tripod with shake reduction off and I used a remote timer. The AF point was set to center focus and the red indicator was dead on the top of the umbrella. The sample images are cropped and I was using the Pentax 50-200 WR lens.
Using AF on the first shot, the image was blurred. The AF on the second shot was tweaked manually and was much sharper.
I bought the K7 to shoot birds and other wildlife and liked the weather resistance feature but the image quality is horrible when I rely only on auto focus. I'm thinking that the AF alignment is way off or there's something wrong with the camera.
Any advice?

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05-08-2010, 04:36 AM   #2
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A couple of things...does this happen often or is it just this one photo you have noticed? Second, try something with a bit more contrast and see if the AF point is more accurate. Thirdly, a slightly better exposed shot may yield better results.

Test something else and see what your findings are....AF hunting is normal to an extent, maybe yours just locked on the wrong point in this particular photo. If all your test shots are thins bad, return the camera for a replacement as it is not normal.

P.S. post the exif data as well...

Jason
05-08-2010, 04:50 AM   #3
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Take a sheet of paper and draw a small dot on it (1/4 inch?). Just enough to be able to get focus.
Set the camera to the Auto focus point detection.

Now with the the paper taped to the wall, hold down the focus button on the camera and move around so the dot moves in and out of each focus area. Watch where the camera changes from one focus sensor to another.

You may find the focus points are not quite where you expect. My old istD has the focus points down about 1/10 the screen height and slightly to the left. I could send for repair or adjust when critical focus location was necessary. I just compensated. It is one way to see if the sensors are out of place...
Although in this example it does not appear anything is in focus.

Other factors also come into play.. if you're relatively close with open aperture and/or long lens you have narrow depth of field. Simply leaning a bit forward or back a tiny bit can cause items to get out of focus as you push the button.
Not that this is your problem, but I often suffer from unconscious leaning. Paying attention to what I'm doing and getting a more stable stance often fixes the problem. (took me a long time to figure this out)
05-08-2010, 08:22 AM   #4
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I tried the dot on the sheet of paper and the auto focus indicator is right on the dot.
How about this as a test.....
I'm going to take a shot outdoors in good sunlight. I'll drop iso to 100 and take a high contrast shot of a static subject with a high aperture setting, say f/11. The subject will be 30' away from the K7. I'll go with AV mode and I'd expect the shutter speed will be at least 1/250. That should give me a broad DOF, good exposure and low noise. I'll shoot from the tripod with a remote sensor and SR off. Being that I usually need the maximum range of the 55-200 WR lens when shooting birds I'll go with 200mm for this test. I would expect the subject to be very sharp when cropped. Is this a good test plan or should I change the conditions?

05-08-2010, 08:30 AM   #5
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I suggest you try this...

PENTAX DSLRs: PART-1. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35

It will quickly tell you if you have any autofocus problems, and how to fix them...

Title states it is for the 20d, but works with any camera with adjustable settings for focus.
I don't have a K7 but I see from the reviews it has similar capabilities in Custom setting No 37.

Dick
05-08-2010, 08:39 AM   #6
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Your camera/lens combo might suffer from back/front focus. Time to read the manual how to adjust the focus.

Hm, must type faster as Dickl beat me on this one. 9 minutes grumph I'm really slow
05-08-2010, 02:28 PM   #7
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QuoteOriginally posted by seachunk2 Quote
I tried the dot on the sheet of paper and the auto focus indicator is right on the dot.
No, that's not really the point. There is rarely any question that the camera is capable of focusing on something right under the center indicator. The question is, how much *beyond* that can the camera still focus on. Keep experimenting with that dot on the sheet of paper, and you'll see that it can focuses on things that are *not* directly under the dot also. Most likely that's what happened here.

QuoteQuote:
How about this as a test.....
Not sure what think it will be testing. It will all come down to whether the camera actually focuses on whatever is directly under the focus indicator, or whether it (legitimately) focuses on something "near" that indicator. Doesn't matter how deep DOF is; if a distant background is "near" that center, the camera might still happen to focus there. You need to make sure you test subject is large enough to cover not only the focus indicator, but the entire area 8around* that focus indicator, as determined by the dot-on-paper test.
05-08-2010, 03:17 PM   #8
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QuoteQuote:
You need to make sure you test subject is large enough to cover not only the focus indicator, but the entire area *around* that focus indicator, as determined by the dot-on-paper test.
That is a really good point. I cannot count how many times the center focus light came on, but the focus was on the background, because my intended point of interest was only partially within the center focus area. The camera has to choose something to focus on, and the camera and I apparently had a difference of opinion. :-)

05-09-2010, 12:27 AM   #9
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I thought about that as well, but I don't think that that is the problem here (I might be mistaken however). The crops don't show anything else that could have been focused on and that is in focus. As these are crops, we can't be 100% sure, but I'm sure OP would have picked up if something would have been in focus.
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