You can read some threads about it but I prefer focussing with the button on the back. You hear the sound and look at the distance scale readout inside the viewfinder. If it looks approximately correct you are good to go. You can push it several times to see if it comes back to the same place. I believe member Socke also likes this focus button.
I think the following is correct. The most extreme focus test would be shooting with the 90 wide open or close to it. Focus on something that has lines to it. That is how the rangefinder calculates distance. Shoot some film. If your shots focus properly it is calibrated well. Your other lenses will also focus even easier unless damaged.
Then just run through all the feature buttons to make sure they are working. Single auto focus, continuous autofocus, exposure lock, manual focus, speeds, shutter. The dial on the left does a bunch of things too.
Read how to turn the lenses properly. If they have been forced in the past some small electronic pieces could become damaged. Then some of the functions won't work. 🙂 🙂
