Jun 4, 2009
I made a 'device' (see pic) to micro adjust my lenses on my 5D2 and I have to say, it works perfect! The focus target and the circles are made with Excel, printed on plain A4 and A3 paper and glued on the wood. The beauty of this thing is that it's clearly visibly where the actual focus area is on the 45 degree angle plane in comparison to the vertical focus plane.
Some rules I followed;
1. mount the camera on a tripod, level the camera and pointing at the, also leveled, focus target
2. the distance from the sensor plane to the focal plane is Focal length * 5 (i.e. 50mm * 5 = 2.50m)
3. use mirror lockup and selftimer (2 sec) with cable release to avoid any camera movement
4. choose the widest aperture (lowest number) for the smallest DOF
5. use the central focuspoint and manual exposure at ISO100
6. autofocus on the vertical plane (by first holding your hand in front of the lens to initiate autofocus) and then take a shot. Repeat this 5 times per micro adjustment step. This means 41 micro adjustment steps (-20, 0 and +20) * 5 shots = 205 shots per lens. Yes, it's an aweful lot of work... So better to find out what's more or less the right MA setting per lens and then go from -10 to +10 around this MA setting.
7. Then evaluate the sets of 5 shots per MA setting and choose the sharpest one, delete the less sharper shots
8. Out of these 21 shots (with each a different MA setting) choose the sharpest one. It's very difficult, if not impossible, to see which shot is 'more in focus' only by the judging the focus target when the ideal focus point is likely reached. The 45 degree angle plane is very helpfull because it shows perfectly where the focus area around the focus point is.
The DOF behind the focal plane should be a little bit bigger then the DOF in front of the focal plane, however, you can choose whatever you like and create a kind of 'personal signature' for your photography. In portraits, for instance, you can increase/decrease the blur of the nose, eyebrows or ears when focussed on the eyes. Allthough you need a f/1.4 or f/1.2 lens for this trick... I also discovered that the amounth of CA's can be controled a bit by adjusting a little + or - the ideal focus point.
In step 6 I discovered that my 50L lens is quit inaccurate in focussing (whats new...). The autofocus 'chooses' a slightly different focal point every time I press the shutter release button halfway. The focus sets at three (or more) different positions, devided something like 20-30-50%. Mind the stationairy setup! All my other lenses are far more consistent in focussing. Maybe it's working better/consistent when the focal plane is not on axis but slightly off axis? Never tried it.
My lenses needed these adjustments;
16-35L II +3, 70-200L IS +2, 15FE +3, 35L -2, 50L +11, 85L II -3.
My old 5D + lenses were calibrated by Canon but I have to say that it's more satisfying to do MA myself and know what's happening exactly.
The Micro Adjustment setting is in the EXIF data and is visible in Canon's DPP (and in the pictures info on 5D2).