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Understanding How to Evaluate Lens Focus Consistancy

A lens can have good optical quality, but a lens also needs to focus consistently to be sharp?  Are the tolerances in the lens loose or is the lens tight?  The tighter the tolerances in the lens, the more reliable its focus.  To check consistency you will need to do dynamic testing - test the image after the lens Auto Focuses.


SPTs Canon Service Adjustment software allows you to test Focus Consistency quickly and easily.  With our software you can electronically measure the focus point on a series of test shots after AF, display the measurement as an easy to understand graph and screen shot the series of test shots for your customer. 


Sharpness relies on two factors:

  • Lens Sharpness.  The combined optical quality of the lens elements.
  • Focus Consistency.  The combined tolerance of the mechanics.


Factors that Effect Focus Consistency

  • The AF Sensor.
  • The combined mechanical tolerances of the Focus Cams.
  • Lubrication. 


Insert video Link ‘Testing Focus Consistency’ here .. under construction



The Tools and Procedures are the same as shown in Understanding How to Evaluate Lens Sharpness / Testing Lens Sharpness.

  • Select the Center AF Sensor using the camera’s Mulit-Controller (Custom Function) or by whatever method your camera uses.  This should eliminate AF Sensor variations.


  • Take a Series of Test Shots using your 3D Target and the softwares Focus Tool.  Does the lens focus to the same point each time?

Defocus between shots so the lens has to Auto Focus for each test shot.  You can repeat the test at several distances.  Your concerntration should be on the consistancy of the point of focus, even if it is not on '0'.


Lens Sharpness and Focus Consistency are combined into a single test, done simultaneously.   You will rapidly gain experience and be to Evaluate Lenses Sharpness using our Canon Service Adjustment Software.  And as importantly you will be able to do the test quickly and present it to your customer in a easy to understand format - Screen Shots with Focus Point Graph.




Series of Test Shots using the Focus Measurement Tool

All Shots focusing at '0'  + / - 1mm



All our Canon Service Adjustment Software offers Help files linked to that Service or Adjustment Function!