Canon EF 70-200mm f/2.8L IS II USM will not shoot at 200mm

[tjwatson11]

I have a EF 70-200mm f/2.8L IS II USM lens that I purchased used.  I use it on a 5D Mark IV.  I have noticed that it is a bit soft and looked into making some adjustments, with the help of Reikan FoCal Pro.  In doing so, I saw that the lens was reported as shooting at 190mm when it was set at 200mm.  Since I wanted to set the AFMA adjustments for both ends of the focal range, this is a problem.  I'm hopeful that someone has had a similar problem and can give me some guidance on how to proceed.  Thanks.  tom

[rs-eos · Accepted solution]

I don't have articles handy, but I believe that is normal. I think the focal length at the 200mm end will vary depending upon how close the lens is focusing on something.

[Waddizzle · Accepted solution]

I have never used FoCal.  But I have done many calibrations.  I have learned that if calibrate both ends of a zoom lens using a focus target at the same distance for each focal length, then you did it wrong.

If you are performing a general calibration, then the target should be about 25-50x the focal length from the camera.  I usually go with 50x.

[jrhoffman75 · Accepted solution]

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@rs-eos wrote:

I don't have articles handy, but I believe that is normal. I think the focal length at the 200mm end will vary depending upon how close the lens is focusing on something.

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That is correct. Focal length is based on infinity focus, and even then there can be slight differences based on design compromises that need to be made. FL are generally rounded off as well.