EOS 3 AF Accuracy Problem with 500/4.5 + 1.4x TC

[matt_hagadorn]

I'm having a curious problem with my EOS 3 and EF 500/4.5L. When I

attach the Canon 1.4x TC, autofocus (only the center sensor is active

with this combination) seems to be innacurate. At first I thought it

was just bad technique on my part (lots of slides of swimming ducks

coming back fuzzy), but then I did some tests on static subjects. The

camera seems to focus just in front of the subject. Its just a hair

off, but its definitely noticeable. Without the TC it seems okay, and

with other lenses (300/4 IS) with and without the TC focus seems

okay. Perhaps its just the higher magnification of the 500 + TC that

makes focus accuracy more critical.

 

Could the focus screen possibly be out of alignment or would this

more likely be a problem with the lens? I plan to take the camera and

lens to a local pro shop, but I'm hoping for a few intelligent

suggestions before I go in. Hopefully they'll let me test another EOS

3 to see if the same thing happens (this isn't the shop where I

bought it).

 

Unfortunately I'm making my first trip to Bosque next week, so if

there's a problem I won't have time to wait for Canon to fix the

camera or lens. I'll either have to rent or rely on manual focus when

using the TC. Bosque isn't the place where I want to learn manual

focus tracking techniques.

[bobatkins]

The long Canon telephotos have a focus adjustment in the lens. It's not user adjustable of course. I'm not saying this is your problem, but it's possible. You may need to send the lens and camera and TC in for service. If you are SURE all your other lenses are OK, tell Canon NOT to adjust camera focus though.

 

I'm not certain just which lenses have this focus adjustment. I know for sure the 600/4 does. I'm guessing the 400/2.8, 300/2.8 and 500/4.5 probably do too. These are the non-IS lenses, I don't know if the new designs are internally adjustable.

[rob_sheneman]

I agree with Bob that you should take your lens/TC/camera to the local Canon service rep. They should be able to adjust the lens focusing. If they can't fix it in time, I'd rent rather than trying to rely on MF.

 

I was at Bosque just before Thanksgiving with Art Morris. We had five days of beautiful weather and good shooting. You'll want to use your 500/1.4 and EOS 3 for flight shooting as the geese and cranes come in for a landing in the ponds and farm fields. Manual focus will be VERY difficult (and frustrating) in these situations.

 

Most people stick to the northern loop this time of year, but don't neglect the southern (swamp) loop too. If you're slow and quite, there should be lots of waterfowl and raptors to shoot. Don't forget the coyotes as they come looking for fresh goose for lunch.

 

Good luck, and good shooting!