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StephenC
10-09-2006, 02:39 AM
Hi there, I've just bought my first dSLR and am still finding my way around it, so excuse me if this is a bit basic.

I have a EOS 400D and both a Canon 50mm f1.8 and a Canon 17-85mm IS USM. The prime lens works great. The 17-85 seems to work fine when at wide angle but can't seem to auto-focus when zoomed. It just shuttles back and forth and if it does settle it is often well out of focus. This seems to be the case on the dummy settings (landscape etc) and the creative settings. I have it set to one shot AF and have tried 9 point AF and centre point AF.

Any ideas or suggestions?

coldrain
10-09-2006, 03:12 AM
Since it is the camera that judges focus, it is hard to say what actually is going on. You are not just talking about very dark subjects and low light photos where focus goes wrong, are you?

If not, then go test some different lenses on your 400D at a local shop. Like 75-300 USM III or a 28-105, or 28-135 IS USM. If they all work without flaw, the camera's AF module is upto spec and your lens should be looked at by Canon. If all these consumer zooms that do not have a big aperture do not focus accurately all the time, then your 400D should be looked at by Canon.

StephenC
10-09-2006, 03:45 AM
Thanks for the quick reply.

I can't decide if it is the camera or the lens. There is no decent camera shop nearby (I bought these via mail order) but I have tried both the other lenses I have. The little 50mm focuses brilliantly, in all circumstances. I also have a really old Sigma 28-200mm f3.5-5.6. This takes its time but focuses well in the end. Unfortunately it isn't complatible with the 400D and gives an err99 if you release the shutter, hence the new 17-85.

With the 17-85 it only has a problem at the 85mm end. I am using it in a well lit room. If I leave the apature at 5.6 (the best it will manage at full zoom) it will still focus at the 17mm end and continues to do so up to about 35mm but the AF struggles thereafter.

I agree with you that the camera handles the AF but as it only seems to happen with one lens I guess it must be that. I'll keep playing and see if I can find a few more lenses to try out.

coldrain
10-09-2006, 03:54 AM
No, it "must" not be the lens, it CAN be though. It does not matter what aperture you use, the aperture only gets closed to the selected value when the actual photo is being made, not when focus is determined.

The 50mm has f1.8 while focussing, the 17-85 f5.6 when focussing. The amount of light that reaches the focus sensors of the camera with the 50mm is a LOT more, and therefore it is easier to focus with a lens that has a larger max. aperture.

Try to focus with the 17-85 on things that actually have some contrast differences and structure. I can to see what you tried to focus on, so maybe you already were doing that but I can not know that. Also try how it focusses when you are outside.

Until you tell or show on what the lens can focus on and on what it has difficulty, it is hard to speculate.
But remember, the 50mm f1.8 will always have an easier job focussing than a 85mm f5.6, because of the amount of light that actually reaches the focus sensors. And the focus sensors look at contrast, that is the only thing they can see.

StephenC
10-09-2006, 04:20 AM
There you go. Even if I end up having to take my camera or lens in for repair, I have learnt something today. Thanks.

I will try again tomorrow, when it is lighter outside and also try to find time to commute to a bigger camera shop and try a few lenses. The Sigma focuses at 5.6 max appature in the same conditions however.

If it turns out to be the lens would you suggest a repair / replacement or a differnent lens. The 17-85 IS USM seems to be pretty universally disliked on these forums (which I didn't know about when I placed my order). What would you suggest as a similarly priced replacement, either a single lens or two cheaper lenses?

StephenC
10-09-2006, 06:18 AM
I'm not sure what the problem was but everything is working now. I haven't changed anything and the room lighting is exactly the same. The USM is suddenly blazzingly fast and focuses perfectly at any zoom. I'm not going to complain but will keep a close eye on it for a few days so I don't miss my opportunity to return it, if it plays up again.

cwphoto
10-09-2006, 06:55 AM
Welcome aboard Stephen.:)

I was up your way on the weekend.

StephenC
10-09-2006, 02:38 PM
Where's Shitney? I assume you came up for the race? Both thrilling and tragic at the same time. Did you get any good photos? I would imaging a 300kph car makes for a challenging shot.

Honest Gaza
10-09-2006, 04:25 PM
Where's Shitney? I assume you came up for the race? Both thrilling and tragic at the same time. Did you get any good photos? I would imaging a 300kph car makes for a challenging shot.

Welcome Stephen....in response to your question to CW....yep, he got a couple of photos of the cars....some weren't too bad, but he'll get better :D (my stomach is hurting)

cwphoto
10-09-2006, 04:26 PM
Where's Shitney? I assume you came up for the race? Both thrilling and tragic at the same time. Did you get any good photos? I would imaging a 300kph car makes for a challenging shot.

Shitney's about three hours East of you - big place by the water.:cool:

Yeah got a couple of pics, you can see a few here:
http://www.dcresource.com/forums/showthread.php?t=24624

noyjimi
10-09-2006, 10:29 PM
Just curious, how far are you from the subject?

StephenC
10-10-2006, 01:25 AM
Nice shots, I especially like the first one. I assume you are using a tripod for a 500mm zoom? You certainly had nice weather for it, you have got to feel for the drivers, stuck in a metal box in that heat. Maybe I'll have got the hang of all this (and bullied my wife into letting me buy some nice lenses) and can get some shots of next year's race.

cwphoto
10-10-2006, 02:59 AM
Nice shots, I especially like the first one. I assume you are using a tripod for a 500mm zoom? You certainly had nice weather for it, you have got to feel for the drivers, stuck in a metal box in that heat. Maybe I'll have got the hang of all this (and bullied my wife into letting me buy some nice lenses) and can get some shots of next year's race.

Thanks Steve.:) No tripod, but a monopod is the way to go for this lens and subject combo. Tripod is impractical for sports.

Pedantic point of order: it's not a zoom.;)

Merlin
10-10-2006, 03:53 AM
Sorry for a bit of a hijack; Question for you cw,

Do you find it at all difficult to frame your subject properly when your stuck at a constant focal range, eg. 500mm?

^_^

cwphoto
10-10-2006, 07:19 AM
Sorry for a bit of a hijack; Question for you cw,

Do you find it at all difficult to frame your subject properly when your stuck at a constant focal range, eg. 500mm?

^_^

Nope. You just need to remember your cricket coach's advice (move your feet). ;) :D

Seriously, non-zooms can be very satisfying. They force you to change position (which changes perspective with respect to your subject) where zooms simply change magnification. And that I think is good practice for a lot of photography - for me it forces me to think more about composition.

Obviously there are times when zooms are extremely practical (event or travel photography for instance).

As a bonus, they're usually brighter - and I'm a hopeless large f-stop junkie like many around here.:o :D

Merlin
10-10-2006, 09:01 AM
hehe, I'll remember that one :) Thanks mate.

StephenC
10-23-2006, 12:17 AM
Going back to my original post.

The camera and lens had been behaving well, after initial problems. Yesterday it stopped working again and I can't work out why. The 17-85mm can't seem to autofocus, it just hunts back and forth. It seems to be worse at the zoom end of it's range and is not dependant on ambiant lighting (I've been out in the sun and indoors), apature settings, camera mode (I've tried virtually every permutation of ISO, mode, metering etc.). I took it back to the shop and they tried my lens on a different 400D with the same problem. They also tried a 70-200mm Canon lens on my body, which worked fine. It would seem to be the lens that is a problem.

As I bought the lens online it seems it now has to make a trip back to Canon, for repairs. It's strange that it seems to come and go.

30D or XTI
10-23-2006, 01:10 AM
Going back to my original post.

The camera and lens had been behaving well, after initial problems. Yesterday it stopped working again and I can't work out why. The 17-85mm can't seem to autofocus, it just hunts back and forth. It seems to be worse at the zoom end of it's range and is not dependant on ambiant lighting (I've been out in the sun and indoors), apature settings, camera mode (I've tried virtually every permutation of ISO, mode, metering etc.). I took it back to the shop and they tried my lens on a different 400D with the same problem. They also tried a 70-200mm Canon lens on my body, which worked fine. It would seem to be the lens that is a problem.

As I bought the lens online it seems it now has to make a trip back to Canon, for repairs. It's strange that it seems to come and go.

Hi Steven,

Did you turn the display off ?? You'll get 100% total control of the camera and the lense AF if it's off, otherwise....The little sensors below the viewfinder can play trick on you as far as quick AF. That sensor is something new to the Canon's product, similar to the new Sony A100. Just a suggestion, hope will solve the problem of your new toy.

Mike @ Las Vegas.

cwphoto
10-23-2006, 01:14 AM
Hi Steven,

Did you turn the display off ?? You'll get 100% total control of the camera and the lense AF if it's off, otherwise....The little sensors below the viewfinder can play trick on you as far as quick AF. That sensor is something new to the Canon's product, similar to the new Sony A100. Just a suggestion, hope will solve the problem of your new toy.

Mike @ Las Vegas.

Mike you've lost me.:confused:

StephenC
10-23-2006, 01:39 AM
I have to confess, I'm a bit lost too. The display automatically goes off when you look through the view-finder. I'm not sure what the display has to do with the focusing but I'm willing to give it a go if it helps. Saying that, I'd be pretty disappointed if a Canon digital (EF-S) lens isn't compatible with a camera that has an LCD. Can you clarify what you mean?

30D or XTI
10-23-2006, 01:50 AM
Mike you've lost me.:confused:

Never mind what I said, I messed up, I thought the sensor works exactly like the Sony A100, then I went back to 1 of the review site, the Canon's IR emitter sensor only turns the display off if it detects our eye or any subject in front of the sensor, it'll not start up the AF....... Well, I messed up.

Here is the review of that site.
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Just above the LCD and below the optical viewfinder are the IR emitter and sensor that detect the presence of your eye or other object (such as your stomach if you have the camera on a strap). This tells the camera that the monitor no longer needs to be on, and prevents glare from interfering with the light coming through the viewfinder. It does not start up the autofocus system as we've seen on the Sony A100; Canon has opted to leave that job to the shutter button.
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