Canon T3 won't focus

[art-hur]

I have a Canon T3, and it will not focus correctly. When I press the shutter release, the lens focusses all the way out then all the way back in. It never stops on anything, doesn't seek a fouc point, just the one out and in movement. I have always had trouble with the autofocus on this camera, but this has become continuous. The lens doesn't matter. I have 3 lenses, and am using the 18-55efs kit lens currently. thanks in advance.

Arthur

[jrhoffman75]

First, reset the camera and try outdoors around mid-day (good light). Try focusing on a house or something with good lines and contrast.

[art-hur]

Thanks for your speedy reply. I had found that seris of things to try, tried them and no joy in the results.Still searching. Thanks

[jrhoffman75]

Does it focus if you use LiveView?

[art-hur]

Suprisingly, it focuses perfectly in liveview. didn't think to try it. Hmmmmm...

[jrhoffman75]

It’s a long shot, but perhaps some dust has settled on the AF Sensor. 

Use a squeeze blower to blow out the mirror box. Hold camera lens opening down so any dislodged material falls out. 

[art-hur]

should the mirror be locked up? Where exactly is the AF sensor? Is  canned air too strong for this? BTW thru the lens the screen itself looks pretty dusty.

[jrhoffman75]

If your camera can do it then lock mirror up. AF sensor is at bottom rear of mirror box. Never use canned air. Besides too strong (and could damage shutter) it contains a propellant that could deposit in camera. 

[jrhoffman75]

[deebatman316]

DO NOT use canned air a bulb blower is enough for this task. Mirror lock up should be used for this. The AF sensor is underneath the reflex mirror in the camera.

-Demetrius

Current Gear: EOS 5D Mark IV, EF 16-35mm F/2.8L III USM, EF 24-70mm F/2.8L II USM, EF 50 F/1.8 STM, EF 85mm F/1.8 USM, EF 70-200mm F/2.8L IS III USM, 430EX III-RT, 470EX-AI & 600EX II-RT

Retired Gear: EOS 40D, Sigma 17-50mm F/2.8 EX DC OS HSM & EF 28-135mm F/3.5-5.6 IS USM