Originally posted by konraDarnok I hate to even bring that up, but if you're using Marc Sabatella's technique of photographing a news paper (or book) at 45 degrees -- and you see more lines of text are in focus above the line you're focusing on than below that line, you've probably got a back focus issue.
That's sort of true, but also kind of misleading. For one thing, when people speak of backfocus, they are generally talking about autofocus, not manual focus. If your camera has consistent BF with manual focus, this is a matter of the the focus screen being misaligned relative to the sensor (or vice versa). It has nothing to do with anything that can be fixed with the focus adjustment menu on the K20D.
Second, it's actually *normal* for more to be in focus behind than in front - that's the nature of optics. Although the convention that says it should be 2/3 in back, 1/3 in front is overly simplistic - it really should be much closer to 50/50 than that at most focal lengths.
But most importantly, the fact that the viewfinder will always show *more* being in focus than actually is going to end up in focus in the picture means that iot is kind of pointless to talk about how much is in focus in front of versus in back of the main focus point, because the viewfinder gives you no way to actually be sure what the main focus point is. It's showing you a broad area and saying "the main focus point is somewhere in here", but that's as far as you can tell.
That is, you might be *aiming* for a certain line of text, and the viewfinder might be showing it to you as in focus, but that doens't mean it is actually the mian focus point - the viewfinder is showing you *several* lines that are in focus, and you really have no way of knowing - aside from performing this test and practicing - which of them is actually the main focus point.
The only way you can really say a camera has a BF problem with manual focus is if things are in focus in the picture but *not* in the viewfinder when shooting wide open. That's pretty rare.