Focusing problems?

Do an auto focus micro adjustment on your Canon EOS camera.

Article and photos by Loftus Viljoen

It is often said that some zoom lenses e.g. the Canon 100-400mm L USM IS lens, has a problem focusing on full 400mm zoom as being “soft” and how many times have you wished that you can just slightly adjust the focusing to get a sharper image?

In some of the Canon cameras like the EOS 5D Mk II or the EOS 7D there is a setting you can use to do these adjustments. Normally you will not require this adjustment, but you may use this adjustment if a certain lens gives you a “soft” focus that you do not want.

I came upon this adjustment quite by chance after a discussion on the focusing problems some people have on the Canon 100-400mm L USM IS lens especially at 400mm.

The adjustment under discussion is on the Canon EOS 7D camera – check your manual to see if your Canon camera has a similar custom adjustment setting.

When you go to custom functions under C.Fn III-5 there is an AF Autofocus/Drive AF Micro setting. You need to roll the setting to number 5 which will appear in the top right hand corner [the 5D Mk II has the same function under C.Fn III-8].

On screen you will now see 3 settings:

0: DISABLE [normally this setting is highlighted]

1: ADJUST ALL BY SAME AMOUNT [using this setting will adjust all lenses you are going to use by the same amount]

2: ADJUST BY LENS [this will give the camera the ability to do adjustments for a specific lens or lens and extender combo.] Up to 20 lenses can be stored if it is registered on your camera. Once you have connected a registered lens the point of focus for that lens will be shifted automatically each time you change lenses.

You need to select one of the above settings by pressing the OK button. With setting 1 or 2 selected you must now press the <INFO> button to view the adjustment settings. You now can make fine adjustments for the AF’s point of focus in ±20 steps (-: Forward / +: Backward). The adjustment amount of one step will vary depending on the maximum aperture of the lens. On the INFO screen you will see the description of your lens – check to see if it is correct.

For the AF micro adjustment I set my camera at Av on maximum of F5.6 for my lens and then stabilized the camera on a tripod as not to get camera shake which could influence the sharpness/focus of the exercise. I started off by going to -10 then -5 then ±0 then to +5 and lastly to -10. This gave me 5 shots to see where the best adjustment would be.

Set your camera at quarter slice L [Jpeg] and remember for each reading you need to set the adjustment [OK] before taking the shot – it will revert back to the last registered reading/setting so make sure that you have OK’d the setting before taking the shot.

To clear the settings you simply go to the “bust bin” on screen and delete.

Just a couple of tips:

· It is recommended that you do the adjustments at the actual scene you want to photograph as this will give a more precise adjustment.

· If you want to use an Extender in setting 2 the adjustment will register both the lens and extender as a combination.

· Please note that the registered AF micro-adjustments will be retained even if you use the “clear all” setting under the Custom Function main menu. You will have to clear the micro-adjustment setting manually and then set 0: DISABLE.

Here are the pictures I took on the Canon 100-400mm L IS USM F4.5-5.6 lens at f5.6 on Av priority:

The photo above is standard without any adjustments and the zoom opened at full 400mm : it seems quite sharp but when it is cropped and enlarged it looks like this: