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Unusual auto focus problem
Old 11-12-2005, 09:08 AM   #1 (permalink)
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Taya manually focused at Virginia Key

I have to work sooooooo hard!


This probably means it's time to send the camera in to Canon, but here's my problem. In the middle of a shoot yesterday the auto focus system suddenly failed to achieve focus lock. The selected focus point would light, the lens would hunt, but the lens never achieved focus lock and the camera wouldn't fire.

Obviously I switched to manual focus and finished the shoot (oh, the horror!), but while shooting I occasionally noticed the focus point lighting up (that happens in manual mode as a signal you have manually achieve focus), and then when I'd switch to auto focus the camera would achieve focus for a few shots (like two) and then fail again. Sounds like (as in "sounds like") some sort of electrical contact problem but I haven't been able to run it down.

Thoughts? (Oh, the camera is an EOS 10D for what it's worth).

John

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Re: Unusual auto focus problem
Old 11-12-2005, 09:23 AM   #2 (permalink)
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Did you try cleaning the contacts on the lens and camera body with a pencil eraser?
Sometimes that is all it takes to get things back in order.
Mark
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I\'m not sure. . .
Old 11-12-2005, 09:48 AM   #3 (permalink)
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this is the same problem but I found that there certain fabrics that donot furnish enough what ever it is that the autofocus focuses on. Also our studio had to switch from the IS lens because it seemed to lose fine focus in some shots.
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Re: Unusual auto focus problem
Old 11-12-2005, 10:29 AM   #4 (permalink)
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Are you sure you didn't switch the focus to one of the other modes other than "One Shot" and it isn't trying to track your subject??

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Re: Unusual auto focus problem
Old 11-12-2005, 11:20 AM   #5 (permalink)
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I'd second the suggestion to clean the contacts. Also try a couple different lenses. That might help you discover if its a camera or lens problem.

Nice shot, for a MF shot. ;-)
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Re: Unusual auto focus problem
Old 11-12-2005, 01:36 PM   #6 (permalink)
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Sounds like a problem solved by Nikon about a decade ago. I'm sure that a top notch company like Canon has solved it as well (I ain't knocking Canon, or bieng sarcastic.) On my Nikon F4, it has some difficulty when I'm shooting on continious auto focus when I hit something that has a lot of similarly textured and colored area. I usually switch to single or manual, or I just focus on something else that will give me sharp focus and throw on the AF lock.

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Re: Unusual auto focus problem
Old 11-12-2005, 06:15 PM   #7 (permalink)
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I've shot tens of thousands of shots with the Canon 10D and 20D and the auto focus has always worked very well on many varied and different subjects. You can have a potential problem if you are using a rather slow variable fstop Zoom lens. Suppose the lens is 4.5-8 as its max fstop range. That mens as you zoom you're zooming out where f5.6, 6.3 and 8 become the aperature that the camera is using to focus with. For many lens, this will then be the fstop being used to do the autofocus. In the Canon manual it makes it clear that when you stop down to 5.6 or further, that the autofocus will be less accurate if not impossible (at about f8 I believe). I only have one lens that has this problem, and I just do the focus before zooming (when the fstop is wider) and then zoom out for framing of the photo. So that is one possible reason.
Naturally it could be a connection issue in which case cleaning will help. Or it could be a bad lens, which can be tested by changing lens, or it could be a problem with the camera.
cheers,
rfs
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Re: Unusual auto focus problem
Old 11-13-2005, 01:57 AM   #8 (permalink)
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[ QUOTE ]
I've shot tens of thousands of shots with the Canon 10D and 20D and the auto focus has always worked very well on many varied and different subjects. You can have a potential problem if you are using a rather slow variable fstop Zoom lens. Suppose the lens is 4.5-8 as its max fstop range. That mens as you zoom you're zooming out where f5.6, 6.3 and 8 become the aperature that the camera is using to focus with. For many lens, this will then be the fstop being used to do the autofocus. In the Canon manual it makes it clear that when you stop down to 5.6 or further, that the autofocus will be less accurate if not impossible (at about f8 I believe). I only have one lens that has this problem, and I just do the focus before zooming (when the fstop is wider) and then zoom out for framing of the photo. So that is one possible reason.
Naturally it could be a connection issue in which case cleaning will help. Or it could be a bad lens, which can be tested by changing lens, or it could be a problem with the camera.
cheers,
rfs

[/ QUOTE ]

Wow... I must be the unlucky one.. I owned two 10D bodies,...and I now own a 5D & two 20D bodies, and I've found that they all suck to hell when working in overcast lighting, and especially shade light.. there is just something about that low contrast lighting that is inconsistant with them.. much worse for any camera, is back lighted subjects... that can get ugly..

I use fast primes too.. My slowest lens / lenses,...( minus the 10-22mm 3.5 - 4.5 EF-S lens) are f2.8.... I seem to have more trouble with the 135mm f2.0 on the 10D than I do on the 20D bodies,...and the 70-200mm f2.8 L,....sucks on all three different models.. I don't know exactly why,...but I have captured many nearly focused shots with them,... I often get better results when manual focusing them.....especially when shooting action..

[img]/ubbthreads/images/graemlins/frown.gif[/img]

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Re: Unusual auto focus problem
Old 11-13-2005, 02:10 AM   #9 (permalink)
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That's a very unusual sounding problem you have there John.. I'll bet you that if you got the camera fixed, you will probably only be able to reclaim about that amount + about another 1/3rd more after you sell it on ebay......so,...is it even worth fixing? I put a brand new shutter into my first D30 body,...along with getting the whole thing adjusted, and the latest firmware updates,...that cost me exactly what I sold it for... 432.00.. [img]/ubbthreads/images/graemlins/frown.gif[/img]

The bellow photo was taken with my 5D body... the AF is a LOT better, but it still has slight issues in overcast & shade lighting.. The more I shoot with the 5D, the more I appreciate it.. I have over 9,000 exposures on it already.......that's what...?? 3K / week..? [img]/ubbthreads/images/graemlins/grin.gif[/img] I'm diging it!

JP

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Old 11-13-2005, 02:33 AM   #10 (permalink)
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In addition to the DSLRs, I have a Canon G5 point & shoot, that I generally like a lot for casting, parties, location scouting, etc, but as with its predecessor (to me), the G1, it will occaisionally refuse to focus after successfully focusing on the same type image for several shots. In typical "only me" fashion, I had a model come see me the other day who wants to get into Playboy, so I had her throw on a bikini to do my usual sequence of casting shots. I set her up in front of a plain tan colored wall, and we get about 20 shots - headshots, 3/4, front, back - with the G5 and its built-in flash (these are only for MY eyes, my files, just need something to reference her with). The focus locks in, flash goes off, pictures are totally sharp. Then she takes off her top, and after the second frame of topless, the camera refused to focus. I could watch it rack right through the focus point, and fire as soon as she was unrecognizable, 10 times in a row. I hadn't changed anything, and I did try using manual focus, but I don't really know how that works on that camera, so I said screw it and told her to get dressed. After she did, I wanted to try a couple shots in her sweater, and of course they were perfectly sharp. Now someone tell me how I explain that to a Canon tech.

Regards,
Andy Pearlman
Andy Pearlman Studio
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