Auto Focus issue: I have a Canon XSi with both the 18-55 and the 55-250 kit lenses. Lately, both lenses sometimes have problems in auto focus, trying to focus but failing to zero in on...

bish Loc: Tully NY

I have a Canon XSi with both the 18-55 and the 55-250 kit lenses. Lately, both lenses sometimes have problems in auto focus, trying to focus but failing to zero in on the perfect focus. Not sure if it's a contact issue in the electronics at the camera or what. Anyone else seen this behavior?

nyweb2001

I rarely use Auto Focus. In most of my landscape shots the camera really doesn't know what I want to focus on. These cameras ARE advanced today, but they can't read our minds !

JimH Loc: Western South Jersey, USA

bish wrote:

I have a Canon XSi with both the 18-55 and the 55-250 kit lenses. Lately, both lenses sometimes have problems in auto focus, trying to focus but failing to zero in on the perfect focus. Not sure if it's a contact issue in the electronics at the camera or what. Anyone else seen this behavior?

AF looks for shiny stuff. High Contrast. If that's not what YOU'RE looking at as a focus point, that's why your shots seem out of whack.

Try setting the CENTER spot only, instead of the whole grid. That way, the AF focuses more on what's exactly in the center of the frame.

Use a smaller aperture - this will make DOF greater.

Center spot and f/16 will make almost ANY scene look good except maybe a closeup of a bug on a leaf.

ShakyShutter Loc: Arizona

I though we were suppose to focus on the subject closest to the camera. Isn't that why the mfg's created that feature in the first place?

charlessmall18

One fundamental fact about auto-focus: the camera does not and cannot measure the actual distance to the subject. No auto-focus camera sends out an infra-red or radar beam and measures the reflected signal. They all INFER focus by looking for maximum contrast between area of differing reflectivity.

MtnMan Loc: ID

I haven't seen that issue. But if both lenses are doing it then it is unlikely that the lens that is the problem.

Starting at the contacts to the camera isn't a bad idea. It can't hurt to clean them.

I would first suspect some setting in the camera. I know I sometimes forget that I set something for some purpose that later had an undesired effect. The obvious place to start is the settings that control focus....although it may even be something more subtle.

I have a Nikon and there are actually three settings that affect focus. One sets the type of focus, the second the focus area, and the third, which applies only to certain focus modes, has you use the control wheel to pick one of eleven points for the focus. You know what's coming next: "read the manual". It may have a troubleshooting section.

Regards,
Larry Leach

bish wrote:

I have a Canon XSi with both the 18-55 and the 55-250 kit lenses. Lately, both lenses sometimes have problems in auto focus, trying to focus but failing to zero in on the perfect focus. Not sure if it's a contact issue in the electronics at the camera or what. Anyone else seen this behavior?

Jay Pat Loc: Round Rock, Texas, USA

1. Maybe, you are too close to what you want to take a picture of.

2. If you are taking a shot of two people and the camera center focuses in between, background will be in focus and the people won't.

3. Subject may be out of Depth of Field for the settings (aperture).

4..... I haven't thought what 4 would be......

Post the image you are having a problem with, along with settings.
We will do our best to figure this out.
Pat

Armadillo Loc: Ventura, CA

bish wrote:

I have a Canon XSi with both the 18-55 and the 55-250 kit lenses. Lately, both lenses sometimes have problems in auto focus, trying to focus but failing to zero in on the perfect focus. Not sure if it's a contact issue in the electronics at the camera or what. Anyone else seen this behavior?

Try this suggestion:

Snap on a lens.
Looking trough the eyepiece select the subject for sharp focus.
Depress the shutter button half way down and hold it there.
Re-compose your image to what you want and then press the shutter all the way down.
this is know in most cameras as "Focus Lock" and may also provide a primary and secondary exposure measurement.

Michael G

MtnMan Loc: ID

Hi,

Which reminds me of one of those potential subtle settings I mentioned that can affect both lenses. The Nikon has a setting in which you can tell it to not take the picture if it isn't done focusing or you can select to go ahead and take the picture regardless when you push the release all the way.

If that got changed to allow shooting whenever you press you might get unfocused images where you did not before. The lens isn't done focusing when the pic snaps. It would happen with both lenses.

Regards,
Larry Leach

Armadillo wrote:

quote=bish I have a Canon XSi with both the 18-55... (show quote)

stephen f. rich

Auto focus lenses seek the nearest reflective surface to the camera. Try setting the camera to manual. Also the manual mode allows you to choose a different f/stop which can give more depth of field. The smaller the aperture (f16 or f22) the greater the depth of field. If you wish to control your selective focus, the larger apertures (smaller numbers, e.g. f5.6 , f4 or f2.8)can offer sharp focus at different points within the frame and you select these ranges. If you wish the background to be soft, use a large aperture. Proper use of depth of field can be an important aspect in shooting. film cameras have a DOF scale on the lens barrel. Also, auto focus cameras have a difficult time with the color green. Good luck, Stephen

MtnMan Loc: ID

Hi,

I never heard that about green. Why?

Regards,
Larry Leach

stephen f. rich wrote:

Auto focus lenses seek the nearest reflective surf... (show quote)

bish Loc: Tully NY

Ihanks for all the suggestions. This is not a problem of not understanding how the camera functions work. I've been using this camera extensively for 2 years now with approx 40,000 shots with no issues before this, so it's looking more like an electrical issue with the camera. I'll try cleaning contacts first, if that doesn't work, I'll probably take it in to my local dealer, they're pretty good. I just wondered if anyone else had experienced similar issues. Thanks again.