Micro Focus Adjustment Revisited
I was in the Eastern Arctic. It's a very harsh and rough environment. It's cold, it's windy, it's dry, it's windy, it's dusty, (did I say that it's very windy with a very cold wind from the North Atlantic?), very wide temperature difference... There is a reason why professional bodies are so much more expensive than "regular" cameras. The sealing, the weather proofing is very expensive with Canon and Nikon cameras. How does Pentax do it?
The temperature differences, from -5°C/23°F outside to +25°C/77°F indoors (in the summer), can wreck havoc on the micro-focus adjustments of the AF by contracting and expanding the internal parts of the lenses and the camera. The micro-focus adjustment of the auto focus is to compensate for the minor variations of the lens as compared to the theoretical/engineered design.
- The body of the camera must be straight and at 90° of the base of the target. A tripod with a head that has a bubble level is "mandatory" and is more accurate that the electronic level sensor, at least on my 7D. Using a bubble level that fits on the camera's hot-shoe is not good enough. I have tried a few, from the ones that fall straight out of the hot-shoe, to the "better" ones, i.e. more expensive. By checking with the electronic level of the camera and a carpenter level, they were off by as much as 10°. No camera manufacturer guarantees that the hot-shoe is exactly perpendicular (90°) to the sensor.
- Do NOT use the
Live Viewmode. The
Live Viewmode uses the image on the sensor for focusing and should never need any MFA. You MUST use the "regular" focus.
- The best focusing mode is the
Spot AFmode. The purpose of the MFA is to tell to the motor to add or deduct an increment for the focusing so the camera needs to know exactly where to focus for getting the "correct" measurements.
- The place should be "bright enough", so that the focusing is clear to you and to the camera.
- The distance? That depends! It depends on the wind, the weather, the age of the captain... and who you listen to. Some people say 50 times the focal lens, SpiderCal, the Lens Align people, say 10 times the focal lens. I say the usual distance that you use the lens the most. Some lenses are mostly used for portraits, i.e. closer, some lenses are mostly used for landscapes, i.e. far away... You decide...
- Download a focusing chart: I use a Pentax chart but it works great and is easy to use: Autofocus adjustments for Pentax and Download the focusing chart.
Canon 7D: C.Fn III -5 - AF Micro Adjustment
My adjustment procedures
- Place a small cardboard at the back of the middle portion, so the middle portion is straight without any sag.
- Place the camera on a sturdy tripod and head.
- Set the focus type to Spot AF. The Spot AF must be enabled with C.Fn III -6: Select AF area selec. mode
- Use the self timer or a remote shutter, take the photo at +10MFA, another at 0MFA and another at -10MFA, then check.
- Adjust the lens by +5 or -5 in the "correct" direction, then repeat until you are happy within 2MFA or 1MFA.
- If the combination camera/lens front focuses: + numbers: add
- If the combination camera/lens back focuses: - numbers: subtract
By The Way, this is also applies to Nikon, Pentax, Olympus, Sony...