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Understanding Focus Compensation
  • Would it be correct to say it is basically not possible to get 100% AF focus, only very close because of some mechanical and maybe optical tolerances?”  Peter / Accurate Instrument Servicing Pty Ltd

 

        Correct!  

 

Most lenses aren't made accurately enough to focus perfectly, but they should back or front focus consistently. So a lens contains a data file called ‘Focus Compensation’ which tells the camera body how much the lens back or front focuses.

 

 

  • Lens Focus Compensation:
The purpose of Lens Focus Compensation is to make the lens give the best focus for all cameras. It assumes the Camera Body AF systems are in good calibration.  
 
This is not an AF adjustment, Lens Focus Compensation is used by the camera body as part of its AF calculations.

 

 

  • Technical Information:
  • Lens Focus Compensation is only calibrated for the central AF frame in the view finder
  • It has separate calibration values for different types of AF sensor in the central frame
  • It has separate values for different zoom settings
  • It has separate calibration sets for different EOS  AF Systems

 

 

Canon Lens Professional Software:

  • Help / Using the software / Lens Operations Menu / Focus Compensation-Adjustment Overview