Canon 100 f2.8 Macro Users please come in.

Some might have already read my previous post so here is one more specific to the MACRO version owners. One big question for you guys.
Has anyone noticed that this lens focuses slower in low light conditions? I've noticed that the focusing mechanism focuses really slowly in low light conditions. I don't mean that it searches , I mean that the focusing ring as seen through the distance scale window moves really slowly indoors in low light. When I use the lens outdoors the focusing mechanism moves back and forth very fast. I also notice that when I leave the lens cap on and press the shutter halfway it moves back and forth really slow and upon removing the lens cap it moves back and forth really fast. My 28-105 with Ring-type USM moves very fast with and without the lens cap. I'm confused. The same thing happens on my old EOS 33. Did I get a faulty lens or is this normal? Any suggestions are greatly appreciated and welcome. Thanks.

David, mine does the same. I believe it's due to the low light condition as you said. It focuses faster when it has more light. It's the same for my other lens. As a matter of fact my 50mm f/1.4 focuses extremely fast in low light condition, even faster than my L lenses (they are f/4). As you can see from my test shot, the result is absolutely okay. I would not worry so much.

Thanks Leorooster. I'm glad I don't have to go through the trouble of returning it now. I owe you one.

You're welcome.....btw, let me know how's your efs 10-22. I am consider this lens. If you get a chance, please post some pics. Thanks.

As soon as I get it I'll post some pics. I have very high expectations for that 10-22. I only hope that the EF-S line doesn't get phased out too soon.

I am pretty confidence that the EF-S line would not be out for a while. Let's cross our fingers. Thanks.

Just tested my 20D/100 F2.8 for you, and mine does the same. When there's lots of light it snaps into place quite quickly, in low light it's slow and hunts a bit.

Thanks Tim. You guys are great!

Ddellatella/Leorooster​. Perfectly normal and expected. Every macro lens you will handle is similar.

Recognize HOW FAR the heavy glass elements have to travel on a tiny gear train inside of a macro lens to have AUTOFOCUS continuous from life size to infinity, and the arrangement of the floating elements for a distortion free flat field, and we'll all have sympathy for the engineering challenge!

Recognize that an f/2.8 macro really has about 1/4 of that amount of light reaching the back for focus. You lose about 2 full stops at life size focus in the lens. It's like trying to focus with a 100mm f/5.6 in low light.

Heck, I'm not even sure I need autofocus on the 100mm macro, except when I'm not using it as a macro. When any macro lens, or any telephoto lens, can't focus lock and goes out-of-focus hunting, they REALLY go out of focus because the elements travel far hither and yon. Takes a while to come back.
That's one reason for the FT-M feature on the lens.
Most users just pre-focus estimate and then manual focus in lower light
Most users will try and focus on a higher contrast tone in the scene
If you're not a macro distance, use focus limiter switch.
Well-heeled users will buy a Series 1 Canon, with a big bright viewfinder. My partner at work has the 1DMkII with 180mm L macro. Both manual focus in the VF and autofocus speed improve dramatically.
The 20D does have a nice coarse ground glass VF focus screen that "snaps" in and out of focus when manually focusing macro. They built it that way for that purpose. It's likely the best VF focus screen in a bad digital 1.6x VF world.

Best of luck and hope that makes you more sympathetic. J.
Want to really have a shocker? Mount your 100 macro on an EOS-3 or even EOS 7 film SLR and see what macro focus looks like in a full frame world... Someday in digital at middle class cost for me.....

Thanks J Rabin. Excellent point about the heavier element. I guess I can start to cut the UPC code off the box for the rebate now that I learned that this movement is normal. Muchas Gracias Muchachos.