C.Fn III -5 - AF Microadjustment

Are you front focusing? Are you back focusing? That's where you adjust the link between the camera and the lens.

Why is the combination of the camera and the lens front focusing or back focusing?

Please note that this apply to all camera manufacturers and not just Canon.

The camera is built to a standard. Depending on the quality of the camera, the standard will be from within 1%, up or down, at the high end to as high as 5% to the low end of the camera scale. Depending on the type and the manufacturing of the lens, the variations can also be up to 5%, up or down. Now take the camera at 3% down, and the lens at 3% up, a perfect match. A camera at 3% down and the lens at 3% down and now we have severe front focus.

Settings

0: Don't do anything. It's the perfect match between your camera and all of your lenses. This is usually after you send your camera and all of your lenses to Canon for calibration.

1: Adjust all the lenses by same amount. It's usually because your camera is screwed up! I would send mine to Canon for fixing and calibration.

2: Adjust by lens. The adjustment is specific to each lens. The Canon 7D can keep track of 20 different lenses. The camera keeps track of the lenses by serial number and not by lens type.

My adjustment procedures

1. Download the focusing chart: It's a Pentax but it works great and is easy to use: Autofocus adjustments for Pentax and Download the focusing chart.
2. Place a small cardboard at the back of the middle portion, so the middle portion is straight without any sag.
3. Place the camera on a sturdy tripod and head.
4. Set the focus type to Spot AF. The Spot AF must be enabled with C.Fn III -6: Select AF area selec. mode
5. Check your focus with live view and magnified to the max.
6. Use the self timer, take the photo and check.
7. Adjust the lens by +3 or -3, then try again until you are happy with +1 or -1.