24-70 L focus problems. Lens? Body? *pics included*

[Booshanky]

I was taking a few pictures in my crappily lit office today and I noticed that some of the pictures were coming out quite blurry. At first I attributed it to camera shake (slow shutter speed for crap lighting), but then I decided to do some tests and I got some weird results. I'm not entirely sure how to interpret them so I'm just going to post the results and see if anyone here knows what might be going on.


Here's the situation. I've got two 300D bodies at my office, one is mine, one is the companies. I put my camera on a tripod with the 24-70 2.8L lens on it and leaving it at 24mm and f2.8, I take a picture of the light switch on the wall. It comes out super blurry.




BUT! when I zoom in to 70mm, take the auto focus, then set it to manual and zoom back out to 24mm and take the picture, the focus is great.




Strange right?

So i tried it with the other camera body and it seems much better. It still seems very slightly out of focus while getting the focus at 24mm rather than 70mm, but lightyears better than my camera body.




Pictures of other objects show the same problem on my camera body, but look fine on the work camera body.




So I immediatly figured that I've just got something messed up with my focus on my 300D body, however I noticed this discrepancy in a photo taken with the work camera body.



The lightswitch (what I was focusing on) looks to be in focus in both photos, but notice that the dell logo on the printer is out of focus on the photo where I focused at 24mm, but it's in focus in the photo focused at 70mm then zoomed back out to 24mm.

Normally I would have attributed it to a narrow depth of field because it was being taken at 2.8, but both photos were taken at f2.8.




Do i have two bad camera bodies, one slightly worse? Do I have one bad camera body and a slightly bad lens?


If it's a shoddy camera body I'm not too concerned, but I just bought this lens so if it's focusing incorrectly I'd like to send it back for recalibration sooner rather than later.



Thanks for any help.
-Mark

[StealthLude]

its probably the lens... I would take it into canon for a focuc calibration..

[august23]

How long have you had these bodies? They might be reaching their shutter limit? Not sure. Maybe someone with a bit more experience can help.

[Booshanky]

I've had my body for about 2 years, this camera at work was a refurbished model directly from canon that we got about 1 year ago.


And stealthlude, if it was just the lens then wouldn't it show the same problem regardless what body I put it on?

[august23]

I think the bodys life is up, one of em at least. On the other hand, you could have one bad body, plus a bad lens.

[Booshanky]

wow, these things have a 2 year lifespan? That seems ridiculously short. Are all canon Dslr's like that?

[august23]

No. But it depends how much you shot with it.I think the rebel series has a 50,000 shutter life or something like that, while the xxD series and up have around 100,000.

[Booshanky]

Does anyone know a way to somewhat objectively test sharpness and focus for the lens?

[Booshanky]

Originally Posted by august23

No. But it depends how much you shot with it.I think the rebel series has a 50,000 shutter life or something like that, while the xxD series and up have around 100,000.

Ahh, I doubt I've hit that limit. I'm guessing I've just got a bad body. That doesnt bother me much because I'm going to be getting an XTI soon. But since I just blew 1200 bucks on this lens I'd like to make sure that it's 100%.

[august23]

Try it on a friends body if you can. If not, send it to recalibration, the worst they could do is send it back and say its fine.

[Lester Wareham]

With parafocal lenses the suggested focus proceedure is to zoom to tele focus and then zoom to whatever you want.

I think the 24-70 is parafocal from memory.

However I would expect the 24mm end to be much better than that.

What was the lighting level in exposure terms?
Is it as bad if the lighting level is a few stops better?

[canonphotog]

Definitely a light switch problem!

[sumyungguy]

First picture EXIF
Camera Model: Canon EOS DIGITAL REBEL
Tv: 1/40
Av: 2.8
ISO: 100

Second to last EXIF
Camera Model: Canon EOS DIGITAL REBEL
Tv: 1/30
Av: 2.8
ISO: 100

Do you have any shots that where manually focused?? So theres something to compare these to..

[Big Mike]

How long have you had these bodies? They might be reaching their shutter limit?

Even if the shutter life was up (which I seriously doubt)...what does that have to do with focus?

[Booshanky]

Originally Posted by Lester Wareham

With parafocal lenses the suggested focus proceedure is to zoom to tele focus and then zoom to whatever you want.

I think the 24-70 is parafocal from memory.

However I would expect the 24mm end to be much better than that.

What was the lighting level in exposure terms?
Is it as bad if the lighting level is a few stops better?

Oh the lighting is godawful. Two overhead flourescents.


I'll try it with a flash in a few minutes to give you an idea if that's the case or not.