I've done an AFMA calibration Reikan Software. Assuming this was properly executed, do I need to take the results seriously? All my lenses do suffer from astigmatism, and also my new Canon 24-70 f2.8 ii USM has problems: "Your lens is exhibiting a significantly higher astigmatism factor than other users. (mounted on a canon 5Dmarkiv.) This could indicate internal element misalignment in your lens."

Do I need to return my lens to the shop?


2 Answers 2


Does the lens make pictures you are pleased with & in particular do you notice the technical problems? If so then perhaps. If not then only if you are worried that this problem might somehow reduce the value of the lens & you plan to sell it at some point.

A lens is just part of a machine for making pictures: if the pictures are fine the lens is fine.


Roger Cicala, founder and all around lens guru at lensrentals.com, probably said it best in his blog entry: There is No Perfect lens

Expecting any lens to be perfect, even the one that's supposedly the "best ever made" and according to the marketing materials solves every problem known to man - at least until its replacement is brought out a few years later and we find out how many problems the old one had that the new one now solves, is unrealistic and a surefire way to be disappointed if one tests a lens to its limits.

Having said that, if all of your lenses demonstrate the same astigmatism when using FoCal, it could be an indication that your test setup is not properly aligned. For FoCal or any other focus calibration method the results are only as accurate as the degree to which the test target is properly aligned with the camera's sensor. If your test target is tilted in one direction or another with respect to the camera's sensor, then your results will show defects due to the varying distances each part of the test target is from the sensor.

The FoCal method uses a flat target which must be in a parallel plane with the camera's sensor. It has a module that assists you with getting your camera and target aligned. Even if you are not using the FoCal software, to use a flat target it must be aligned. The easiest way to do this is to choose a sturdy, undistorted wall mounted mirror and adjust the camera position until the Center Focus Point is aimed at the center of the camera's lens in the reflection. Then tape your test target to the mirror with the center of the target on the spot your camera is already pointing at.

The same is true if the lens is not properly square with the camera's sensor. This could be due to a misalignment of lens elements. It might also be due to either the mounting flange of the camera not being square with the sensor or the flange ring on the lens not being square with the optical axis of the lens.

Flat target testing methods will reveal pretty much every minor flaw a lens has. That's the main reason we like to use flat test charts when testing lenses. Even when a camera/lens combo is adjusted just as well as is possible, minor flaws will be visible in the test pictures of a flat target if looked at with enough scrutiny.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.