Originally posted by PentaxPoke The primary uncertainty in the angled chart methods is that the center AF point is not an infinitessimally small dot. This means that when you focus on the line, AF might lock when the line is at the bottom of the sensor region, or at the top.
I am not sure what you mean. If you center the line horizontally across the sensor, it's going to focus on the line, period. The only issue is the *thickness* of the line, but that's what, a millimeter? Very few lenses have a DOF so shallow that this is is going to be an issue (although to be sure it can happen at macro distances). Usually we're looking at a zone of acceptable focus that is probably like 100 times larger than the thickness of that line.
FWIW, angled charts in which the target is the border between solid black and white blocks rather than a black line of non-zero width against a white background are also available - I just haven't liked other aspects of those charts that I've seen, so I keep coming back to Jeff's.
Quote: The best way to fix BF or FF on the k20d is to not use the angled charts, but simply set up your camera, and use text on a wall. Adjust the lens correction + or - until it is perfect.
That works too, but it has issues too. For one thing, requiring more trial and error to figure out out what's going on. But also, if there is any variation - say a lens that needs different focus adjustments at different distances, or a zoom that needs different adjustments at different focal lengths - you'll drive yourself crazy trying to figure out what is going on. The angle method lays it out on the line for you. But once you've identified the nature of the problem that way, I'd agree the type of method you're describing could work well for actually doing the calibration, because it's not like you can actually *solve* either of the problems I mentioned.