AF shutter lock (10D)

[bryantg]

Hi - I was using my 10D today with a rental 28-105 lens on a soccer picture day. Tons of kids, teams, etc.

Several times I went to shoot, and got nothing. No shutter release at all. This was always when I pulled the zoom back for a team shot - never on a zoomed in shot at all.

Switched to a backup, finished my part, came home and hit the book. It looks like the auto-focus wasn't focusing, which was preventing the camera from releasing the shutter. This was on a cloudy day, no shadows, but kids in white or blue soccer jerseys against green trees, or even just shooting a red & blue soccer ball on the ground (i.e. pretty high contrast). Again, If I pulled all the back on the zoom (28mm), it would usually not shoot, push it in to around 38-105 and it was fine.

The guy using the 20D next to me had no problems, and the 1DmkII I borrowed as a backup was fine. Just the 10D with this lens.

Is this just plain user error, or could it be dirty contacts not consistently moving the af in the lens? I hate blaming equipment, but it *was* a rental lens. At least now I know to switch to manual focus.

Thanks,
Greg

[robertwgross]

There are all sorts of things that would inhibit a shot. Lack of sufficient light is one. If the light is too dim for the camera settings, it will not fire. We don't know what shooting mode you were in, so the rest is pure guesswork.

If it turns out to be associated with just that one lens, then that would be a good thing to avoid. As a general rule, though, if a lens or the mount is bad, then you'll get some kind of camera error message relating to the lens or else Err 99, which could be the lens.

---Bob Gross---

[bryantg]

Thanks - of course I can give settings, but it's a bit harder to give a light sample so they make sense :) . manual, iso200-400, 1/90 & 1/125, f8-11 (depending on the thickness of the clouds), AWB. Again, no problems with individuals at about 60mm, but pulled back to 28-35 for a group, it wouldn't shoot. And not consistently, either. Either a group of kids (faces, arms, shirts, etc) or red & blue ball on the grass at 11am should have plenty of contrast. At the same time, I think it would be unusual to have a lens act that way, so I just don't know.

Greg

[robertwgross]

We still don't know what mode you were shooting in. For example, Tv, Av, etc. Where was the autofocus drive mode? For example, single shot.

---Bob Gross---

[bryantg]

err, I actually did say manual in the previous post. For the rest, it's one shot AF, eval metering, no compensation, large/fine jpg, center af point, single frame drive mode. Continuous numbering <g>. Tried a new, fresh battery, too!

I was just noticing that if I take a lens (Canon 50mm 1.4) and in a poorly lit room aim at a solid color, I can get the af lock to work (i.e. blinking circle, no shutter release). What's different is that it rolls the focus all the way in and out before giving up, and I don't remember it doing that yesterday. (The rental was returned yesterday, as it was rented by the company I was shooting for, so I'm stuck with guesswork).

So I'm still not sure.

Anyway, I do appreciate your thoughts. My main job is as a studio recording engineer, and I hate not knowing why a piece of gear is acting the way it does.

Thanks,
Greg

[robertwgross]

err, I actually did say manual in the previous post.

The term "manual" means different things. Manual exposure mode is more specific. Manual focus is more specific.

Yes, when you are in a dimly lit room and try to get the camera to autofocus on something, it will often hunt in and out and then stop without any autofocus lock.

You have several alternatives. You can try to adjust the settings to provide more sensitivity, you can try to autofocus on some subject with better contrast, or you can kick the camera over into flash mode and let the autofocus assist give the camera something better to work on.

---Bob Gross---

[bryantg]

ah - sorry about the manual confusion.

You bring up an interesting point. I've been using a flat black road case about 2m away from me here in the studio as a test object. If I aim at it with no flash, settings definitely too high for the amount of ambient light (like 5.6 at 1/90), it won't focus. If I flip up the built-in flash, it does it's little modeling rapid-fire flash (or whatever it's called), but it still won't focus. If I put on a Sigma EF-500 (which should be a 550EX, but that's a whole 'nother story :) ) in ETTL mode, it doesn't do the modeling thing, but the camera seems to be able to focus better. With the Sigma, it got everything I tried the af on (black road case, gray berber area rug, LCD monitor that was turned off), and only had trouble when I aimed into the darkened tracking room. This is the flash I had on yesterday when I had problems.

Do you know how this might be? Does the flash use an alternate method (ultra-sonic or something) to determine distance, and if that failed, could it mess up the af?

See, the more I think about it, the more bits I remember that might help.

Greg

[robertwgross]

Canon flash units like a 550EX or 420EX output a faint red pattern that allows the autofocus mechanism in the lens and the camera to lock onto the subject.

So, the flash doesn't exactly determine the subject distance on its own, but it does something so that the lens and camera can figure where to lock the focus.

When the shutter button snaps, the flash quits the faint red pattern and outputs a very low-level standard flash pop, which is called the pre-flash. That light bounces off the subject and hits the exposure sensors in the camera, so metering occurs. Then, a tiny fraction of a second later, the main flash pop blasts out, and the camera has already told the lens and shutter what to set for to get that main exposure right.

Anyway, if you want a focus target, stick a bright red thumbtack in the center of a ruler or a yardstick, and set that on a slant between the floor and the wall. Then set the camera on the same level as the thumbtack and try to see what autofocuses and what does not.

---Bob Gross---

---Bob Gross---

[bryantg]

Found the problem.

Borrowed another 28-105 lens, had the same problem. Zoom out to 28-35mm (roughly) and no shutter release. It would AF, though! I could manually take it out of focus, hit the shutter release, it would focus, and then the light would flash saying that it couldn't focus. This was on a high-contrast background.

Took it to a camera shop, they couldn't think of anything, and couldn't find anything about it Canon's tech notes, but thought it might be a compatibility problem with the older EF lenses and the digital body. Grabbed a new EF 28-105 mk II, and it worked fine.

So, apparently the problem is that some Canon lenses are not compatible with the 10D. Note that a 20D at the studio worked fine with this same lens, and as it's not even on tech notes, it might not even be a wide-spread problem, but limited to some bodies.

Greg

[blackviolet]

could you take photos in manual focus mode? did it err99, or just not take photos?

were you in aiservo mode?

also, you borrowed a 1dmk2 and used it as a backup??!?!

[bryantg]

It would autofocus, then not shoot. If I flipped the lens to manual focus, it would then shoot (and be in focus! - which is, at least, a workaround). This was in One Shot AF mode. No errors at all, it would focus, and then the "focus confirmation light" (little round light on the right hand side) of the viewfinder would flash, indicating no focus. I could manually take it out focus, hit the shutter release again, and it would focus and then flash the confirmation light.

They let me borrow the 28-105 lens that was causing problems (mk I) so I could play with it some more. It happens in any AF mode (One shot, AI Focus, AIServo). It only happens if I'm zoomed out further than ~40mm (at about where I expect 40mm to be, it works). Anything else that would be pertinent that I should play with?

The 1D belonged to another photographer there and she had been pulled over to the registration desk, so when mine had problems, she shoved it in my hands and said, keep going! Yeah, some "backup"! Wish I could have that happen all the time :shock: .

Greg