In fact – both.
Unfortunately I don’t read my articles, I only write them… When I opened a 5dMkII with shutter failure, I looked to the cmos if it is fixed on washers (like all of the old cameras), or on springs (like a lot of new ones, for example the 50d https://canonrepair.wordpress.com/2013/01/13/shutter-replacement-in-canon-50d/ ).
They were washers under the CMOS. OK, I disassembled it, without any former measurement.
It was a mistake.
The CMOS was fixed with 3 torx-head screws. “…this kind of screw permits to transmit relative big torques, without axial force…” as I have written before, and it is use to make possible the adjustment of the cmos height without pressing it down with the screwdriver.
But there are no springs under. Yes – the springs are substituted with 3 small rubber tubes (or washers), which You can see on the right side. As You fasten the screw, the cmos base plate will lay on the metallic washer, and the rubber will be compressed as You try to fasten the screw.
As a first try I assembled the body with 5 cm back focus on 100 cm 🙂
After that, I made the measurements with my own method https://canonrepair.wordpress.com/2012/12/30/how-to-adjust-the-position-of-the-sensor-in-a-dslr-camera/. The method makes possible to adjust the distance and the inclination of the sensor in the same time.
After making the calculation, doing the adjustment, and the first assembling, the focus was exactly in the middle (verified on only the central sensor).
….. In fact, this was true only partially – only when using a vertical target line.
How is this possible?
On this never disassembled, never repaired camera, the horizontal and vertical sensors from the centre AF point had a difference of ca. 1 cm on 100 cm. This is possible to demonstrate using a selective focus chart – in normal usage You will only see some bad focused pictures – when the AF automatic chooses the horizontal line instead of the vertical one. And this depends on what You have pointed the camera, if it has a better contrast on a vertical or a horizontal line.
This will be in my next post.