Yesterday I finally got around to checking the precision of the auto-focus on a couple of our lenses. By doing so, I learned a little something that I wanted to share. To do the test, download a focus test chart. I got mine from “Focus Test Chart“. You could actually improvise and make your own, but hey, the thing is free. Anyway, five photos follow. All shots were taken using a 1D Mk III. You can click on them to get a closer look.
Photo #1: my simple set up on the kitchen table. You’ll need a tripod and a cable release. Simply lay the test chart on the table and set the camera at a 45 degree angle.
Photo #2: Canon 24-70 L f/2.8 shot wide open (1/60 sec). This shot shows a very slight front-focus situation which definitely won’t do for a tack-sharp ring shot that you HAVE to have when covering a wedding event. And, this is the lens we normally use for the ring shot, so now I know we must either use manual focus at this f-stop, or go to say f/3.5.
Photo #3: Canon 50mm f/1.4 shot wide open (1/250 sec). This shot indicates a slight front-focus as well, but more than that, it shows how soft this lens is when wide open. Not nice! I had no idea how soft this lens is wide open.
Photo #4: Canon 50 mm f/1.4 shot at f/2.8. This shot shows how sharp this lens can be. Nice!
Photo #5: Canon 50 mm f/1.4 shot at f/2.0. This is the minimum f-stop I’ll ever use with this lens.
I’m glad I took the time to do this bit of research. I learned a lot by doing this, and I’ll do it with each new lens I purchase.
Chris
