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07-04-2010, 07:17 PM   #31
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Please use this to check your lens. As I said before, if you are not happy with the lens just ask for a re-imbursement and buy something else. It isn't likely you will like your next copy of it either.

QuoteOriginally posted by Ubuntu_user Quote
Oh here's a photo from a wedding I attended yesterday... Center point focus, f/5.6 I put center focus point on the brides face, locked the focus, then reframed the image. What do you think?

Photoshop.com - IMGP4663.JPG
As far as I see, the lens is focused in the man with the kid in the lower left corner. So that means that the lens is back AND front focusing with the same camera. Since this is not likely, I can only call for user error.

07-04-2010, 07:53 PM   #32
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QuoteOriginally posted by summonbaka Quote
As far as I see, the lens is focused in the man with the kid in the lower left corner. So that means that the lens is back AND front focusing with the same camera. Since this is not likely, I can only call for user error.
After checking the EXIF on this pictures, something is not quite right. You have the fix center focus locked, and if you did locked (pressing half-way on shutter release) and recompose, you did not move much. And yet, the focus point seems to be on the lower left corner as Summonbaka suggested.

If you have another lens, try to see if you can replicate that. If so, the fix center-focus selection on the camera does not function properly. The distance between the bride and persons sitting in the lower left corner is quite large for any front and back focusing issue. Do you use half-press of shutter to lock focus or do you use AF button to lock focus? It appears to me that the camera is selecting on some things else and not the center point. Try multi-point focus selection option and leave it in center, see if you get the same result. If you get different result, then the "fix center-point" focus button setting is not working.
07-05-2010, 05:35 AM   #33
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I also noticed that the shutter speed is 1/20, which could also be a contributing factor if you are not holding the camera steady enough. For indoor shots without flash, TAv mode is mostly helpful as you don't want to keep the shutter speed and aperture constant at the same time. Hopefully, it is user error and not problems associated with the lens or the camera. Good luck...
07-05-2010, 08:02 AM   #34
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Thanks aleonx3 for your help! Like you say, the focus point is way way off from the center. I didn't hardly move after I locked the center focus on the bride (I use the AF lock button, not the shutter). I took a few photos and every single one of them turned out like that.

Here's a keyboard shot. The H key was exactly in the center focus point. Camera was tripod mounted.
Photoshop.com - IMGP4751.JPG
I know, hangu, my previous pictures are horrible. Probably the worst I've seen... Sorry about that. Hope this one is better for you.

07-05-2010, 08:51 AM   #35
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QuoteOriginally posted by Ubuntu_user Quote
Thanks aleonx3 for your help! Like you say, the focus point is way way off from the center. I didn't hardly move after I locked the center focus on the bride (I use the AF lock button, not the shutter). I took a few photos and every single one of them turned out like that.

Here's a keyboard shot. The H key was exactly in the center focus point. Camera was tripod mounted.
Photoshop.com - IMGP4751.JPG
I know, hangu, my previous pictures are horrible. Probably the worst I've seen... Sorry about that. Hope this one is better for you.
I'm not saying your photos are horrible. I'm saying you had a knack for picking horrible test subjects.

Judging by the keyboard, (I hope you turned off shake reduction when you tripod mounted it) it seems like it's back focused by a centimeter or two, not a huge problem. Just compensate for the back focusing in the camera body. By the way, you're negating the benefits of using a keyboard as a test subject by slanting it... When I said 45 degrees to the subject, I meant along the Z-axis, not both the Z and X-axis.
07-05-2010, 10:14 AM   #36
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QuoteOriginally posted by Ubuntu_user Quote
Ah! I agree. It is as though the camera just "chooses" to disregard the center focus point and then focuses somewhere else. If it were a problem with the camera, then wouldn't I have the same issue with other lenses?
Hard to say. Two or three pictures don't prove anything one way or another. Could be simple coincidence that you've noticed this on one lens but not another. Still, I'm thinking it very unlikely it's a camera problem (using a different focus point despite you selecting the center). The fence seemed to be a simple matter of it happening to notice the background behind the fence instead of the fence itself. Cameras don't read minds. Not sure on the wedding shot, but I unfortunately agree you seem to have a knack for picking test subjects that don't really work well - way too much in the scenes for the camera to select from even when telling it which focus point to choose. In the wedding shot, I'd have not been the least bit surprised to see the camera focus on the background. The fact that it focused on something in the foreground makes me wonder, but I could still imagine a whole bunch of explanations (like maybe you weren't *really* on center point mode, or something walked by the exact moment you were focusing and the camera caught that).

Last edited by Marc Sabatella; 07-05-2010 at 10:21 AM.
07-05-2010, 10:29 AM   #37
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QuoteOriginally posted by hangu Quote
Judging by the keyboard, (I hope you turned off shake reduction when you tripod mounted it) it seems like it's back focused by a centimeter or two
You can't conclude that from this test at all. The H might have been dead center, but the actual focus sensor is fairly large, and would easily have included the back edge of the key and perhaps the key "above". Which is to say, the camera could have legitimately focused exactly where it did.
07-05-2010, 05:25 PM   #38
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QuoteOriginally posted by Marc Sabatella Quote
You can't conclude that from this test at all. The H might have been dead center, but the actual focus sensor is fairly large, and would easily have included the back edge of the key and perhaps the key "above". Which is to say, the camera could have legitimately focused exactly where it did.
I'd disagree based on the tests I've conducted, but I also know you're probably more knowledgeable than I on this subject. However, if that were the case, then his lens is spot on focus-wise, right?

I really want to see him photograph a brick wall from the distance of 10-15 feet. I think that test would be better.

07-05-2010, 06:14 PM   #39
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Ubuntu_user, I would start something very basic to test the AF focus point change works; here is an example of testing my 50-135mm lens (actually testing SDM). I have the focus point set to the middle right off center aiming at the ripe raspberry. The DOF 2.8 is shallow but the shutter speed is more than adequate to ensure no camera shake. Can you find something similar to that and make sure that it is not the camera issue?
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07-05-2010, 09:10 PM   #40
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QuoteOriginally posted by hangu Quote
I'd disagree based on the tests I've conducted
Disagree with what specifically? If you've done tests to determine the size of the focus sensor, then you cettianly know they are much larger than the little red squares that can optionally display on some cameras. The only question might be whether they are so large they encompass the rear edge of the H key. Sure looks likely to me. but in any case, if you're trying to ascertain something like that, it's time to stop guessing and put away all poorly conceived ad hoc tests, and download a real focus test chart where you *know* the camera won't choose anything but the target.

QuoteQuote:
if that were the case, then his lens is spot on focus-wise, right?
If it chose to focus on the rear edge of the "H" key, then it does appear it did so successfully, but it's hard to say because a keyboard makes a poor test subject. Again, that's why people gave gone to the trouble of producing focus test charts that not only present a clear target to the camera, but also present the user with a clear way to to evaluate the results.

QuoteQuote:
I really want to see him photograph a brick wall from the distance of 10-15 feet. I think that test would be better.
No, it wouldn't. A brick wall shot stragith on would not show you if focus was in front or behind the wall. And a wall shot at an angle is a wall that you don't know *where* exactly the camera focused. Again, focus test charts exist for a reason - they are designed to eliminate the common (and they are *very* common) errors people make when trying to test focus on their own.
07-06-2010, 03:19 AM   #41
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QuoteOriginally posted by Marc Sabatella Quote
Disagree with what specifically? If you've done tests to determine the size of the focus sensor, then you cettianly know they are much larger than the little red squares that can optionally display on some cameras. The only question might be whether they are so large they encompass the rear edge of the H key. Sure looks likely to me. but in any case, if you're trying to ascertain something like that, it's time to stop guessing and put away all poorly conceived ad hoc tests, and download a real focus test chart where you *know* the camera won't choose anything but the target.



If it chose to focus on the rear edge of the "H" key, then it does appear it did so successfully, but it's hard to say because a keyboard makes a poor test subject. Again, that's why people gave gone to the trouble of producing focus test charts that not only present a clear target to the camera, but also present the user with a clear way to to evaluate the results.



No, it wouldn't. A brick wall shot stragith on would not show you if focus was in front or behind the wall. And a wall shot at an angle is a wall that you don't know *where* exactly the camera focused. Again, focus test charts exist for a reason - they are designed to eliminate the common (and they are *very* common) errors people make when trying to test focus on their own.
In my experience, the focus sensor is either small enough to focus correctly on the H key or it's more sensitive in the very middle. I feel the letter H has more contrast than the edge of the keys and the focus sensor seems to lock on it well. Of course all keyboards are different.

I think someone has suggested the OP to use a focus chart but for whatever reason he hasn't done it yet and has opted for other lesser and more convenient targets. I figured a keyboard was convenient enough for the OP to use.

The OP claims that most of the problem is with focus beyond 6+ feet, which a focus chart would not help with.

Frankly, I think it's 99% user error with a possibility of a tiny bit of back focusing. Based on what the OP has said and his selection of test subjects, I'm not entirely convinced that he knows how to use the equipment properly.

I figured a brick wall straight on would at least tell the OP if the camera is focusing properly or not. He wouldn't know whether or not it's front/back focused but at least it would cut down on the possibility of user error. Right?
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