40D focusing issue

[shybull]

My 40D will not focus with the center point or the top three other points. The other focus points work fine. The confirmation light in the view finder (when using the 4 bad focusing points) just keeps flashing and never confirms focus. The other focus points will stop flashing when focus has been achived.  I chose the points individually. I've tried several different lenses with the same results. I took out the focus screen and blew it out. Still no focus with those points. I've had this camera for 7 years or so. It has maybe 40,000 actuations. Is this the sign somehting failing?

[TTMartin]

Likely there is dust interfering with the AF sensor.

When the mirror is locked up you will see some holes at the bottom of the mirror box. The AF sensor is below those holes.

You can try using a bulb blower (don't use canned air) and blow down through those holes to try and clean the dust off the AF sensor.

Note: Do NOT touch the mirror as it can easily scratch, use mirror lockup mode (preferred) or manual sensor cleaning mode to lock the mirror up. If using manual sensor cleaning mode, be careful not to get dust on the image sensor.

[shybull]

Locked up the mirror and used a blower to blow at the AF sensor holes. Not luck. Still not focusing with the same four points. Most of the time it defaults to infinity using those focus points. Off for repair I guess. 

[RobertTheFat]

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@shybull wrote:

Locked up the mirror and used a blower to blow at the AF sensor holes. Not luck. Still not focusing with the same four points. Most of the time it defaults to infinity using those focus points. Off for repair I guess. 

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What's a used 40D worth these days? If it's less than the repair cost, maybe Canon will let you trade it in on a refurb 60D or something.

[amfoto1]

Before sending for repair, double check that your focus screen is fully seated and locked in place. If not, correcting that might be a quick, easy fix.

If it isn't the focus screen and since you have likely ruled out any dust or obstructions on the AF sensor array, I'm afraid it's probably something failed and a bigger repair job.

***********
Alan Myers

San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
FLICKR & PRINTROOM 

[shybull]

I took the focus screen out and put it back in. No difference. I replaced the original screen with the S screen when I first bought the camera