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Old Jun 16, 2003, 11:52 PM   #1
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Default 10D, objective focus test. Mine has front-focus

Well, I decided to try a back/front focus test with my 10D. I would like to hear your opinion of the results!

I took two pictures at a shallow angle, then two more at a steep angle, of a sentence I printed out on a regular piece of paper. It seems that my 10D has a front-focus bias. The results are here:

http://www.pbase.com/barthold/focus_test

The first picture shows the front-focus the best. I Focused all pictures on the word "test" (zoomed out images) or on the letters "es" in the word "test" (zoomed in). I used the center focus point. The word "test" is 0.75 inches long by 0.375 inches tall. The whole sentence is 8.75 inches long. Distance from front of camera body to the word "test" is 29.5 inches. Lens used Canon EF 28-105 3.5/4.5 USM II. The camera was on a tripod.

Now the question is, how bad is this? Enough to return the camera? What do you guys think? Most of the DOF is in front of the spot I focussed on. As far as I understand DOF roughly 1/3 should be in front and 2/3 in the back.

Thanks!
Barthold
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Old Jun 17, 2003, 9:13 AM   #2
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Doing a front/back focus test is actually rather difficult. There have been a lot of posts about this on other forums... someone finally got out the Canon official book and showed people the Canon approved method of doing it. Check out this link:

http://photography-on-the.net/forum/...?TopicID=10948
Or this link:
http://forums.dpreview.com/forums/re...essage=4942449

and I have a few more if you want them. :lol:

Among the discussion of info about this issue, they refer you to write ups about the proper way to test the focusing of your camera, and the proper target to use when testing focus.

I worried about this problem when buying my camera, but after reading a lot about it, I concluded that not many actually have the problem and that I should just buy it and try it. If I notice that too many of my shots were out of focus, then I'd do the test.

Eric
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Old Jun 17, 2003, 11:17 AM   #3
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Hi Eric,

Thanks for the links. Will read them! You seem to always have a link to a discussion of whatever topic :-) An endless supply of links :-)

I did notice that portrait pictures I take are out of focus at times. That can of course be user error, or a moving subject, but it could also be the camera (or a combination).

Even if my home-brew test was not Canon approved, the results of the test I did are still interesting. They are not what I expected. If I focus on two letters I expect those two to be the sharpest, not the letters next to it.

Barthold
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Old Jun 17, 2003, 10:58 PM   #4
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One thing to check is to see which focus points was in use. You can do that from the File Viewer Utility. There is an icon on the tool bar (the 6th one from the left) which enables it. It isn't an intuitive icon, so just leave the mouse over it and the tool tip text will appear which is perfectly clear ("Display AF Point".)

A common problem is if you let the camera select the AF point, it can pick the wrong one. I quickly disabled this and only use the center AF point because its more advanced than the others (can focus on both horizontal and vertical contrast.) And it's also easy to focus/meter and then recompose from that AF point.

I have had very good luck with focusing, but on two which were really important to me nothing was in focus (could be me and camera shake) but it was also clear that the area closest to being in focus was in fact below the AF point which registered focus. Weird. So it can happen. When it really matters, I take many pictures. Sucks, but that is part of the tradeoff for buying the 10D over the 1D (or 1Ds.) They have much better AF systems. Canon cut costs somewhere, and the AF system is one place. I don't like it, but I don't blame them.

I have so many photography links from when I was researching which camera to buy its scary. It still amazes me that I can remember them and find the one that I want. I've actually been slowing down recently. I don't read dpreview as much (probably because I've burned out on it... and I've got pictures to view and edit!)

Eric
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Old Jun 18, 2003, 12:50 AM   #5
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Hi Eric,

I'm almost always using the center focus point, and re-composing when necessary. The tests I did where with the center focus point. The cool thing about a fast DSLR is that you can take many pictures, and simply throw away the ones you don't need. I'm just still looking for a small device to store my pictures on when on a trip. Even a 2 Gb memory card is not going to do me much good. 20 Gb would be more like it :-) Last trip I took my laptop, which is great for viewing and editing, but it is a bit big. But I digress.

I looked at your focus test links. I'm going to try one of them, that way I'll have some more standard test to compare to. I'll post the results!

Barthold

Barthold
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Old Jun 18, 2003, 6:02 AM   #6
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Bench test is one thing, but real life is another...

When I checked the AF accuracy on the 10D like in my other posting, it was 100% kosher (and I'm sure everyone will too). What's bothering me is sometime especially on portrait I believe the camera is not spot on (with the center AF sensor only). It could be subject movement after the camera has focused (but I doubt it when it was a group portrait) and the shutter speed was not an issue either!

I'm keeping note on where the focus point is locking on ie skin tone or eyeslash/hair line and try to get a handle on this... Will let you guys know... Or I could be all wet for that matter :lol:
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Old Jun 18, 2003, 9:12 AM   #7
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My Inlaws are visiting and their two cats are now running wild through the house. One was particularly cute by getting on top of the kitchen cabnets and then crawling around like Snoopy through the grass ala "the world war one flying ace."

I took a few pictures to show their owners when they got back. One of them was *clearly* not in focus. F4 & 1/60 with fill flash at 28mm(x1.6) and IS on should be crips (using the 28-135). I got one which was amazingly crisp and clear.... so it can do it. But there isn't enough detail in the cabnets to see if it miss focused there.

So I do agree, some times the 10D just seems to focus wrong. But it's only often enough to make me believe I'm not imagining it. It isn't 40+% or something... that would make me take it somewhere.

I agree about taking so many pictures. I do it some times just to make sure I get the shot. Other times just to see what works. I put about 160MB in 96 images onto a 512MB Cf in 3 hours. I'll probably switch to RAW soon now that I have a feeling for how many I shoot.

Eric
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Old Jun 18, 2003, 9:14 AM   #8
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Barthold,

Check out this one:

http://www.ssdonline.com/detail_page...token=21548403

if the link doesn't work go to:

www.ssdonline.com
the click on FlashTrax 30GB Photo Player on the home page.

Cheers
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Old Jun 18, 2003, 9:54 AM   #9
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Eric

On another note there's much less DOF on the 10D as well, especially with my f2.8 lenses! So may be it's just a matter of adjusment (or re-adjustment) to a different gear... I guess one can be really sloppy with the AF with the D7's large DOF inherent in theses cameras. Whereas the 10D can pick out fraction of an inch, and that was the DOF effect that I was after all! :lol: :lol: :lol:
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Old Jun 18, 2003, 1:54 PM   #10
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tuanokc

Interesting product. I hadn't seen that one. I'll have to save a link.

NHL & barthold

On a different forum it was pointed out that there is a common problem which I might be suffering from as well.

That you lean forwards when focusing. Then as you recompose you lean back a bit. This nullifies that focus you just locked. This can only be a hunching at the shoulders and a straiting up... but that can be enough. This alone might be what forces me to pick a tripod over a monopod.

I have found that I just don't get the DOF that I want some times. I don't normally care. I was just trying of the cat's head and to show its location. But when I was taking a picture of a rare and protected turtle I saw in the wild, I just couldn't get the DOF to cover his whole shell and head. I need to do some tests with news paper and keep shifting the f-stop and watch how the DOF grows.

Eric
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