40D autofocus issue

FDuff

Hey guys,

I’ve got a Canon EOS 40D, it’s only 2 months old and it’s been already twice for repair at Canon’s... anyway, I’ve realised there seem to be an issue with the autofocus and I’d like to know if someone else has encounter the same type of issue and how to fix it.

The problem I’m facing here is that in Av mode (aperture priority) the autofocus is off by some distance (enough to have a blurred image when zoomed in at 100%) but if you take a similar shoot in let’s say P mode (auto) or Landscape mode the autofocus is much better, almost perfect.



Both pics were taken on the 40D + canon 50mm 1.8 AF, 800ISO, handheld.
one taken in Av (1/200s) - left - and the other one in Landscape mode (1/20s) - right -



As you can see in the pics I’ve taken, one is sharp, not the other and both were taken with the AF on with the focus done on the right eye of Tweety


I’ve been into photography for many years, I also own some EOS 1VHS gear, and from experience had never had such problem with my gear.

City-Exile

What is the aperture of each shot?

Ricky91t

Obviously a lanscape shot is going to have a higher aperture eg f/8 f/10 if the camera is set is aperture priority the lense will be set to f/1.8 allowing only a very little part of a picture to be spot of focus and sharp the rest will be slightly oof

sasar

I would suggest you do a front/back focus test on your gear:

http://photo.net/learn/focustest/

FDuff

for the Av, f1.8 and the Landscape f5.6.

but that doent matter, if the focus was done on the eye, the eye should be sharp.

reminder: focusing pt is the same on both pics (right eye).

is there any way you can actually adjust the autofocus settings??

FDuff

sasar wrote: »

I would suggest you do a front/back focus test on your gear:

http://photo.net/learn/focustest/

cheers Sasar, I'll check it out and go through some tests tom.

Fajitas!

Is there any chance you could have moved, even slightly?

The fact that the one on the left is at 1.8, and you can see the start of one of the antanae (???) is beginning to come in focus shows that there is some sharpness there. The fact that it's just over his right eye makes me think this is the case.

At 1.8, with a subject so close, DOF is going to be minimal.

City-Exile

Your test can't be accurate when you're hand holding.
With a 50mm f/1.8 it's very hard to get the focus right, when you've got the aperture wide open.
It's a cheap lens & needs you to do a lot of the work.

Have you tried it with another lens?

FDuff

Fajitas! wrote: »

Is there any chance you could have moved, even slightly?

The fact that the one on the left is at 1.8, and you can see the start of one of the antanae (???) is beginning to come in focus shows that there is some sharpness there. The fact that it's just over his right eye makes me think this is the case.

At 1.8, with a subject so close, DOF is going to be minimal.

exactly my point! that's why i took care of NOT moving (even so was taken @ 1/200) and focuse on the eye. the top of the antenna appears to be in focus, which would imply that the autofocus in Av mode tends to focus slight nearer than where it's supposed to be... perhaps I will need to bring it back to Canon for further adjustment.

City-Exile

I'll ask again, have you tried it with another lens?

PixelTrawler

Mount the camera on tripod. You need to ensure that hand motion and lens distance, even a small change, is not throwing out your test.

Take the same shot at same f number, in different modes...

Also it could be the AF in the lens, not the body. I had a Sigma lens recently where the AF was faulty and it needed replacement - sigma said the electronics were scrambled in it. I had thought it was the camera.

Further tests - try a different lens on same body and try the problem lens on a second body. If you get consistent results then you'll be surer or the problem - which will help solve it too as you'll be better able to describe it when looking for a replacement

stcstc

which focus point are you using in the view finder

as said above hand holding with that lens wont make sure of no camera shake

also the lens you are using is not exacly the top of the line lens. try using a piece of L glass


I have owned a 40d (in fact one of the first in the country) and have not had any problems with it, although my 50mm is the 1.4 version.

My main lens of choice is the 70-200 F4 which is tack sharp and have no problems with auto focus

City-Exile

I have used the 40D with the 300mm f/2.8, the 70-200mm f/2.8, the 17-35mm f/2.8 & the 50mm f/1.8
None of them have had any issue with autofocus, but the 50mm f/1.8 is the cheapest lens I've ever bought. It has a plastic housing & is slow to focus. The shallow DOF makes it difficult to get the focus right.