Digital cameras forum: Auto Focusing Problem

From reading your previous questions, I have a good guess that you're new to DSLRs. Just a couple of more questions.

Have you read the manual from front to back?

Do you understand depth of field?

I'm guessing you're using the 40D in auto mode with all focus points active. People can't use a DSLR like a point and shoot camera. The camera doesn't know what subject that you are wanting in focus and usually chooses the closest point with contrast. Since DSLRs have a shallow depth of field then you can easily mess up the photo by having it focus on the wrong area and thus blaming the camera for the problem.

I see you are wanting to do portrait/glamour photography. I'd recommend learning the basics first(exposure, shutter speed, focal lengths, aperture, etc.). You can buy the most expensive equipment you want, but the most important part of making a good photograph is the person behind the camera, their knowledge, creativity, and skill.

You're friends DSLR might have been set up for centerpoint only or he chose his focus points. If you shoot in the green box and haven't set up the AF then it's set to all points active, which is not very good for normal shooting.

If you still think it's the lens then change your AF(auto focus) to center point only and take some photos with one of your friend's lens. If his lens is fine on his camera then it should work just fine on yours. You can also test your 18-55IS lens the same way by doing the same thing, but making sure that the subject is in center when you compose the shot.

Since you're new then you really really need to read the manual. Even if someone has used a DSLR before they need to read the manual to understand the differences/updates to this new DSLR. On dpreview.com's forum there was a slew of people that had DSLR experience and had horrid problems with the Canon 7D not focusing properly. All of them were completely due to operator error and not reading the manual because the 7D has a much more sophisticated AF system that can be tailor set to many more possibilities than their 30D, 40D, or 50D.

I've also seen tons and tons of people new to DSLR who said their lens or camera wasn't focusing properly. Over 90% of them were due to not reading the manual, not understanding depth of field with DSLRs, not understanding the AF system of their Canon DSLR, and using it like a point and shoot. That's the reason I asked so many questions, which I'm still hoping your going to answer the first barrage of them.

With you being new to DSLRs you should expect that you are the problem and work from there first. There is a chance that the camera or lens has a problem but it's almost always the operator error, especially with people with little knowledge of the camera, photography, and who are new to DSLRs.

Lenses can be changed between bodies. The reason I want you to try out his lens is to make sure the body isn't the problem or that the AF setting isn't the problem. You should make sure to set the AF system to center-point only and make sure the thing you want focused on is in that center AF point while looking through the viewfinder.

If the lens is a problem then it would not be off by much...were talking 2-6" off. If you're getting photos that show the focus is off by more than that then it's probably not the lens.

Lastly, did you look at your photos in the software I told you about and looked at the where the camera chose to focus? That might just end the speculation right there without having to do anything with the camera or lens. If you use the software to view the photo, choose to show the focus points chosen, and the thing that is in focus is right in/next to that focus point then you have found out the camera did it's job, just not what job you were expecting it to do.

Are you using a polarizing filter on the lens? That may also cause problems with autofocus.