100mm f/2.8 macro USM - drifting focus

I've done a search and cannot find a related topic.

My 100mm f/2.8 macro USM lens' focus drifts, at least when I am attempting to shoot macro. In this particular case I have it mounted on my Canon 40D and am in the "one shot" mode (NOT in AI Servo). The lens seemed to focus properly initially, but as I continued to partially depress the shutter button, the focus seemed to drift backward (away from the camera) within a second or two of the initial focus.

I put my 70-200mm f/4L IS USM on the 40D, focussed on a subject (partially depressed shutter button) and while keeping my finger partially depressing the shutter button I moved to other subjects at a much different distance - they all looked blurry (i.e., the lens did not continue attempting to focus on any new subjects), therefore I'm assuming the camera is fine.

I've had the lens for 9 months (purchased new) and have only used it very briefly three or four times since then. It's never been dropped. I plan to use it for macros of wedding details (rings, flowers, invitations, seating cards, etc.) and have not had a need to use it much to this point, but I have a wedding in May and I want it working properly. I'm about to send it back to Canon for adjustment, but just wanted to confirm (as crazy as it may sound) that this isn't "normal" for this lens. God I hope not.

Mike

Hate to mention this but 98% of people would not be using AF for macro work = not really an issue.

Yup, what he said. I've noticed the same thing happen now and then with my Sig 180mm macro, and I figured it was just the nature of the beast. I shot some stuff around the house when i first got the lens (handheld), and the focus would go out every now and then. But, I was out shooting some flowers (handheld again) with it and it stayed focused.

Go figure

But, if I'm not out shooting something, I'd be on a tripod with a macro rail and Manual focus.

Thanks very much gasrocks and katodog. I thought about manual focus as a more realistic option after the post. I'll have to explore what tripod options may be more workable on a wedding day.

Mike

Yeah, same thing happens to me all the time, then I realize I need to get off AF. I'm pretty sure that's normal with most lenses doing Macro work.

MJH1 wrote in post #7623160
I've done a search and cannot find a related topic.

My 100mm f/2.8 macro USM lens' focus drifts, at least when I am attempting to shoot macro. In this particular case I have it mounted on my Canon 40D and am in the "one shot" mode (NOT in AI Servo). The lens seemed to focus properly initially, but as I continued to partially depress the shutter button, the focus seemed to drift backward (away from the camera) within a second or two of the initial focus.

I am assuming you are handholding. Have you tried it on a tripod and duplicated the problem?

As I am sure you are aware, at macro distances, the DOF is mm...probably fractions of mm. You may not realize it, but you are probably slightly swaying.

yep, between slight movement and AF adjustment I used to 'get close' with AF via the * button than trim focus with manual, that way the shutter button didnt affect focus. The key thing is practice of course.

jrsforums wrote in post #7625633
I am assuming you are handholding. Have you tried it on a tripod and duplicated the problem?

As I am sure you are aware, at macro distances, the DOF is mm...probably fractions of mm. You may not realize it, but you are probably slightly swaying.

That might be a possibility, OP. Personally that's a big problem for me - I can't get my body to remain rock solid - that, coupled with shaky hands, are a constant frustration for me when I do macro.

I still love it though...

For using Macro lenses, the key thing is practise.
Most of the people use Manual focus to avoid all such attempts

Thanks very much for the comments and suggestions everyone.