Unable To Calibrate
Rarely do we come across a situation in which we are unable to correct for a front or back focus problem. If problems are seen, this is due to either excessive optic (in the lens) or AF sensor (in the camera) displacement or a combination of both.This normally requires a repair to either the lens or camera.
Little did we know that a recent visit by a customer with a problematic Canon EF 24-105mm F4 L IS USM coupled with his 5D Mk IV had already been repaired ! The customer mentioned that he had dropped his lens but that is was repaired by a Canon authorised repair agent. Since the repair though, he had been experiencing problems with lack of sharpness.
Onto The Rig It Goes
When we put the lens / camera lens combo up on the test rig and ran the test, even we were surprised at the amount of lens displacement + 265 correction at 105mm…..
For those of you who are unaware the amount of correction that can be applied in camera is + or – 20 micro adjustments…
For additional measures we also tested the lens on our benchmark 7D Mk2 body.In this case said repair agent had not properly checked the lens or had displaced the optic block (Canon L series lenses can be adjusted or shimmed in either a horizontal or vertical axis).
A word of caution – Without a specialised rig this cannot be performed. The solution – back it goes for repair but probably not to the same repairers….