EF 24-70mm f/2.8L USM Lens focal length mismatch after repair

[sashrof]

Hi I recently serviced my EF 24-70 2.8 1 st generation lens at a local servicing store and upon receiving it back it seems that the lens is wider at 70 mm than my EF 70-300 F4-F5.6.

I took it back to the serviced and they are quite baffled because according to them if the lens was set at incorrectly it would impact focus. The lens is focusing well and is producing sharp images.

I also placed the camera at the edge of the table, connected the 24-70 and placed a 24 inch ruler approximately 4 feet away from the camera until it filled the 24 inches in the frame. I took the 1st shot at 70mm. I then repeated the process with a 70-300 lens and took the second shot also at 70mm. I got about 1.5 inches narrower field of view from the 70-300 mm. 

Really appreciate any feedback on what could the issue be and potential other ways of trouble shooting. Thank you all!

[rs-eos]

Did Canon perform the repairs?

[sashrof]

No it was performed by a reputable local repair shop that works with B&H photo and Adorama 

[jrhoffman75]

Lens focal length numbers aren't always exact. You are reporting about a 6% difference between the two lenses. One could be slightly greater than 70 and the other less.

Did you run this comparison test before the repair?

[sashrof]

I did not run a comparison prior to the repair per se, however I did observe that at 70mm the magnification through my view finder of the 5D mark3 was always greater than 1:1. This is still true for my EF 70-300 where the magnification is slightly higher than 1:1, the 24-70 however shows a 1:1 magnification after the repair 

[sashrof]

The 24-70 needed the superstore mechanism to get fixed as it died and was locked at a very high F stops. The repair shop had to replace the mechanism and realign the glass to canon specifications

[ebiggs1]

Most likely the repair shop didn't do it correctly. There are stops in side that limit zoom travel. Perhaps they are not set correctly.  To align a lens, some lenses require a little disassembly like removing a snap-fit plastic ring or part, however on some you can do it by turning screws on the outside of the lens (not the real outside but inside of that).

No lens has the exact FL that is printed on the lens. The printed FL is a job the ad department does. And they are looking for the best one to put on it even if they have to stretch the limits of credibility a bit. BTW, most lenses have less FL than advertised. Plus the FL can be different at different focus distances combined with FL. Generally referred to as focus breathing. One lens I had was the Nikkor 70-200mm VRI at closest focus it could only manage 135mm equivalent.

[kvbarkley]

Focal length should be measured at infinity focus. Here is a good way to do it:

https://bobatkins.com/photography/technical/measuring_focal_length.html