The focustestchart web site has my focus target of choice - giving the AF sensor a single line to focus on amidst a blank area saves tremendous "did it decide to focus on the edge instead" headaches.Ī) I'm glad I bought the Katz Eye focus screen - it's really nice to have the chance to see when the focus is very close.Ī1) Also, the actual 50D center AF sensor when used on an f/2.8 lens is actually about the center 60% of the split prism center area - much larger than the little box.Ī1i) Test this by getting a bit out of focus, then getting the box near (left/right) a vertical line on a blank paper - get nearer/farther until you find the border where it does, or does not, autofocus. Posterboard was set on the floor at the bottom of my stairs, or leaned against my garage door. Test targets included an 8.5x11 target, the same blown up to 11x17, and a white and black piece of posterboard set next to each other (vertical line contrast for AF!) with a ruler laid next to it, or balanced atop it. My 400 f/5.6L went in for Canon service.Ĭase, I shot a semi-appropriately sized test chart at a 45 degree angle, at each focal length, at a variety of working distances (except the true macro end for the Sigma), center point only (note that for me, 400 f/5.6 excepted, that means I'm using the high precision cross type f/2.8 sensor). I've recently finished micro adjusting my Sigma 50mm f/2.8 EX DG Macro (which registered as if it were a Canon 50mm 2.5 Compact Macro!), 24-70 f/2.8L, and 70-200 f/2.8L IS with and without 1.4x Canon extender II.