Focus Problem with New 70-200L f4 at shortest length.

[Johnny V]

Hello everyone,

I'm new to Canon and the Rebel.

Along with the Rebel I purchased two lenses - the 70-200L f4 and the 50mm f1.4.

Both lenses are sharp for sure - and the 70-200 seems incredibly sharp wide open at f4 but I'm having a focus problem with it. Focuses fine 90mm to 200mm but at 70mm the lens back focuses more than 50% of the time. I have only the center focus sensor set. I can focus on a car's license plate about 30 feet away and the plate will be soft but behind it will be sharp. Also I focused on an object about 250 feet away - part of a house - and that was soft but the house behind it was sharp. This is all wide open at f4 at 70mm. Seems like it has problems focusing at it shortest length. At 200 it's tack sharp.

Anyone know if it's the lens or the camera? I have a couple of more days to exchange it.

Thanks for your help!

John V. :cry:

[drisley]

If the problem doesn't exist with the 50F1.4, then it's the lens, not the camera.

[Johnny V]

Thanks Drisley!

I'll do a little more testing tomorrow just to make sure the 50mm is OK - but it think it's fine.

Best,

John V.

[hank1105]

I sometimes have this problem with my 70-200 f/4 as well. In my case it is caused by the subject matter just being too close for 70mm, if I switch to something else it works out fine. Sometimes I have to switch to MF because the rebel tries to AF but the subject is too close. Can be a pain in the butt sometimes, but I am a noob so I need patience.

Hank

[Johnny V]

Thanks!

All my test shots have been at 15 feet and beyond. I haven't tested today as it's raining outside.

Hope it clears up some!

[Johnny V]

Did some more testing today. And a more confused then ever. Seems like the 50mm also has problems back focusing too. So it looks like it's the camera. But the problem - I mounted the camera on my tripod, so the bottom is a little marked up and I don't think I can return it.

I'll call B+H tomorrow just to see what they say...but I think I own it now.

Geez I don't remember buying/using a new camera was ever this difficult. My old Nikon 8008's auto focus camera was dead-on-focus all the time - still is. And the Fuji S2 I've been borrowing for the past couple years has had no problems either. Neither the Canons my clients use.

[RichardtheSane]

Exactly what test are you doing?

[Johnny V]

I shot real objects.

As an example...

I shot a car's license plate at about 30 feet. I was approximately at 45 degree angle from the back of the car. On tripod with only center focus sensor active I zoomed in to 200mm got focus conformation, shot, then zoomed out to 70mm and made sure focus lock conformation, shot again. This test resulted in the 200mm was dead sharp while the 70mm shot was soft at the plate but had a sharp tail light further back. The tail light was nowhere near the focus sensor.

Shot a cupola on top of a roof using the same technique. 200 was sharp but at 70mm focus was on the trees behind it. And there was plenty of the cupola to focus on at 70mm.

Same problems with my 50mm - always seem to focus back further.

My guess is my Rebel is the problem.

Geez I have a Nikon 8008 that has had perfect 100% auto focus for the past 12 years. You'd think with all this new technology that auto focus would be better than 100%.

When I get my replacement I'm going to take the camera out for ten minutes and shoot. If any of the images are not sharp I'm returning it and getting the 20D.