manual vs auto focus

Do the head-on test first. There are a number of ways the 45-degree test can steer you wrong. If the camera passes the head-on test, you need not even dip into treacherous waters.

transcend wrote:
here is the result of the test.

Taken at 45 degs (as per marking on tripod, may be slightly off).
40mm, f 4.5, 3 foot distance aproximately. On 17-40L

I would assume that at 40mm/4.5 DOF would be pretty decent, would being off of 45deg even a tiny amount make the test worthless? It looks like it is back focusing a fair amount.

Also, as for the diopter, i just tested it and my manual focusing indoor in not so great light is not good. WAY off for now, i wear a fairly bizarre Rx pair of glasses tho (oddly shaped eyeball due to concussions). I matched it up so that AF looks sharp, when looking through it, but obviously this wont work if AF is off.,

http://www.transcendma​gazine.com/random_pics​/focus_test.jpg

this shot is from straight on

http://www.transcendma​gazine.com …s/focus_test_st​raight.jpg

To be honest with you, I don't think your lens is off at all. Your "target" line seems to be pretty in focus to me.

First, judge all images as 8x10 prints of the full image. Canon's tolerances are based on the DoF at 8x10 hardcopy enlargement, no larger. Canon has published at least two documents urging users not to judge AF at high enlargements on the monitor.

Second, remember that the camera may focus on ANY contrast in within the area seen by the sensor (at random, and not necessarily consistently). On the 20D, that area is NINE times the size of the marked central square, so it includes many more lines than the one you focused on. The camera may lock onto any of them and still be within Canon's tolerances.

Third, the camera may focus anywhere within 1/3 of the DoF around the intended plane of focus (using the central AF sensor at f2.8 on the 20D, anywhere within the DoF in in other cases). So in that way, it may show "front focusing" or "back focusing," yet be within Canon's tolerances.

I've pretty severaly myopic myself, and now I'm also presbyopic. The camera viewfinder is designed to place a virtual image about 1 meter in front of your eyes--your eyes are actually trying to focus at that distance, so you should wear whatever glasses you need to focus at 1 meter.

To adjust the diopter settings:

Remove the lens and point the camera toward a large, evenly lit area (a blank, light colored wall will do). Look through the viewfinder at the AF marks. That's what you want in sharp focus.

Turn the wheel all the way to an extreme so the marks are strongly defocused. Then turn the wheel QUICKLY to sharp focus. Don't try to focus slowely and carefully, or you eye will adapt to an out of focus condition. You may have to do it several times, going back to a strongly OOF extreme, then going quickly to correct focus.