Problems with autofocus on Rebel XT

[djdante]

Hey all, I just received my Rebel XT yesterday with a 17-85mm canon lense, and while it takes great shots on manual focus mode, when I try to automatically focus it, all the shots are out of focus. Does anyone have any ideas as to what might cause this?

I have tried just using the middle point for focus, but to no affect.

I have quickly taken two test shots to demonstrate my point. They are not meant to be works of art. Unfortunately due to the sizing cap on this site, the difference is not as pronounced, but you can see that the photo on the right is out of focus.

[Bob_A]

Where was your AF point for these photos?

[djdante]

the AF for the picture on the right was set to automatic, but I already mentioned that centre point focus is no better. The same applies if i do a portrait shot as well. I have a UV filter on for these, but again, taking it off made no difference to the AF problem.

[robertwgross]

the AF for the picture on the right was set to automatic, but I already mentioned that centre point focus is no better.

Does this mean that you let the camera decide which AF point to use? Sometimes we get better results if we manually select the exact point to be used, but it sounds like you have tried that.

I suggest you try a standard focus test (ruler test). That will tell you if your camera/lens combination has a front- or back-focus problem. If there is no problem, then we are back to potential "user errors" which happen frequently for a new user. For example, sometimes a focus problem is claimed, and it turns out to be a camera shake problem.

---Bob Gross---

[djdante]

Thanks Robert, I have done this test, and you can see that the error lies with the autofocus. The question is, how can one get this fixed?

In case anyone asks, YES the focus point was the centre dot, which was resting on the middle line. The image that looks correct is the manual focus, also centred on the dot, but this time focused by myself.

Is this something I am going to have to send the camera back for? I hope not, have gone through hell to get this thing.

[steve.banks]

either my eyesight is shot, or you transposed the 'manual' and 'auto' pictures...

[CyberPet]

If the AF is off, you should have the lens calibrated.

[robertwgross]

The trouble with a front- or back-focus problem is that you don't know whether it is the fault of the lens or of the camera body. When Canon does a calibration job, they can calibrate your lens to their standard body, or your body to their standard lens. For your case, I would send the camera and lens together.

---Bob Gross---