Manual focus issue with 100mm f2.8 usm macro len

[photomike42]

The other day while using this lensin mf mode I noticed that when turning the rocus ring the focus would not change for some time then all of suddenly move with the ring again.  this repeatedly constantly and I could verify it with the lens off camera and watching the focal distance on the lens just stay at a point while turning the ring and then all of suddenly move.

Is this typical for this lens or is this defect?

[ebiggs1]

"Is this typical for this lens or is this defect?"

You have the Canon EF 100mm f/2.8L Macro IS USM Lens?  No, it isn't the way mine works. However, MF is not the easiest thing to do with a DSLR. They really aren't designed for MF any longer.

[photomike42]

Thank you ebiggs1

[MikeSowsun]

I suspect you have the older Non-IS, Non-L, version of the EF 100mm f/2.8 USM Macro. Older USM lenses do tend to wear out with age and some will start to slip just as you describe. 

There is no easy fix and you should really send the lens in for repair. They will probably need to replace the entire USM AF motor.

Here is a video showing how one person fixed a slipping USM motor on an older out of production lens. 

[photomike42]

Thank you Mike