Snow flake, and an naive question on the 100mmL

[wcleung]

I got the 100mmL yesterday. I made a point to quickly test the AF of the lens+camera and noticed nothing before I paid. At home with subjects of better interest, the AF "success" (I don't mean sharp, I mean not blatantly out of focus) rate ranges from
<0.5% for small water condensation on a flat window (so the focus should be easy)
0% for snow flakes (understandingly hard, MF has 2% success rate)
<1% for water droplets sprayed on a CD, to
50% for bank notes.
That's over a total of several hundred shots, handheld.
Is this normal?
Is everyone using MF only (or mostly) for their macro work? (Including in flight shots?)
At some point I was quite worried that either AF or IS malfunctioned, and if not for a word from a friend, I'd have brought the lens back to the store. Pointers to earlier posts on this are appreciated. Since it's a major purchase, I think most of you who know what to expect would not mind passing a word of reassurance or warning.
Many thanks in advance.
Debbie

[CactusJuice]

Keep in mind the depth of field at 1:1 is very narrow, a few millimeters! For macro you need to have it on at least f11. Try something in the range of f11 to f16, f18...somewhere in there. And yes the IS helps but again we're talking millimeters so use at least 1/125, tripod if possible. And expose properly; you're samples are underexposed. I think your lens if fine. Just need more practice

[wcleung]

Many, many thanks! The DOF turned out less than 1mm the first time. Stopping down (so I finally have 1-2mm DOF) and borrowing a little natural sunlight this morning helped tremendously. Debbie

[gmillerf]

I've never had a macro system that supported autofocus, so I can't really tell you what to expect. But, if since you're doing this handheld, I'm betting you're moving the camera too much after you've already autofocused.

One way to test your autofocus performance is to put the camera on a tripod (and use a cable release). Set up a ruler far enough way to focus on angled at about a 40deg slope (so you can read the numbers, but have the ruler exceed the depth of field). Then autofocus on a number in the middle and take a picture. Then view the picture full size and make sure the number you focused on is in focus. Most DSLR cameras will let you compensate slightly if your lens is consistently focusing to far in/out.

There are also fancy tools you can buy that do the same type of testing, but using a ruler works pretty well. I've found that the AI Servo and AI Focus on my Canon 50D are off compared to One Shot focusing mode. So make sure your camera isn't set in a "tracking" focus mode.

[wcleung]

Many thanks. I will certainly test the AF carefully on tripod. Debbie