AF Micro Adjustments on Zoom Lens

[Scott_Witcher]

Hello all,

The latest article by Peter Gregg is about AF Micro Adjustments to calibrate lenses. It's by far the best article I've read on the subject but that's not my point.

The point is that every article I've seen on AF Micro Adjustments to calibrate lenses is done with prime lenses, but what about zooms??? Does the process work the same way and does it work for all focal lengths??

Has anyone tried AF Micro Adjustments to calibrate a zoom? and what were you results?

[AndrewRodney]

According to the doc's with LensAlign, you can (and should) calibrate at the longest zoom focal length, wide open. Might not be ideal for all zoom ratio's but I have to suspect that doing this is an improvement over nothing, assuming at that ratio, its back or front focusing.

[Peter Gregg]

Scott, doing zooms is just as easy as doing primes. You do them at the long end of the lens and at the wides aperture just like on a prime.

This doesn't mean the short end will be correct though. But is IS a good test to see if your lens needs to go in for a service job to have it aligned. If the long end is correct, and you then test the short end and it is NOT correct, you have no control over this and it is visible proof to you that the lens is off on one focal length or the other - send it in.

You can read a more elaborated version of my answer in the Canon 1D forum on this same forum.

Peter

[Scott_Witcher]

Peter, thank-you for the reply. Your article and the post in the Canon 1D forum were very helpful. I checked my workhorse AF-S 70-200 f/2.8 VR and noticed that it is perfect, no AF adjustment needed when at 200mm but when at 70mm there is a bit of front focus. Would I be correct in just leaving things as is, since the focus is accurate at the longer lengths where focus is more critical?