Focus Problems

That article explains a lot, thanks for that!

Funny, just ran into this just the other day when trying to take a photo of some text with very small DOF (not quite Macro distances, but still close to the lense).
The slight change in angle while trying to focus and recompose just made it impossible to get a sharp image.
Took me a couple of tries before I realized what was going on. You just don't notice this with larger distances.

In practical terms, this is an erroneous argument. I understand what is being suggested, but at normal distances it isn't relevant IMHO.

The use of the central focus point followed by recomposing works just fine even for the most critical applications.

For macro work, on a tripod, manual focus is the best option in most cases and the relvant part of the screen is where we look for sharpest focus.

In photography, sometimes the simplest of things can be made complicated quite unecessarily.

Unfortunately it is difficult at times for me to correctly determine the exact point of focus with the tiny view finder. I need to rely on the camera to do the work. For me, and possibly for others, it is an important issue to keep in mind when certain conditions exist.

For those with perfect vision, this is most likely an experiment in futility and would in fact be quite unnecessary.

In theory, a guy with my looks, wit, intelligence, and charm should be rich and famous....in theory.....
javascript:emoticon('')
In reality, I can only speak for hands on results with thousands of portraits under my belt and say I wouldn't recomend something that didn't work for me.
focus, recompose and shoot works for me whenever I'm not using manual.

I focus, re-compose, and shoot. And it works. But in fairness, I try to focus on something that's a similar distance away from me as the bit that I want to be in focus. Focussing on a bollard, then composing on a mountain, is unlikely to work very well.

G

Yeah, depending on the distance, aperture and the lens, the difference is not noticeable. I don't remember if the lens and distance were mentioned in the article linked above, but I would have to guess that for most portrait work this is not an issue. In fact I'd be hard pressed to believe there would be a problem for the example given at that link.

I certainly have never noticed it myself (not that I have much experience in that arena, but still, I know if the final shot looks like crap)

But, for a recent photo I tried to do, I used a 50mm1.4 at about 18 inches. This gives a DOF of about .25 inches (.5 cm?). When focusing and recomposing on a point distance (on the same focal plane) 2 inches form the intended focus point you get a focal length that is about .1 inches longer.
If the physics holds true and the range of DOF is roughly 30% in front of the plane of focus and 60% in back, this .1 inch difference will cause the intended plane of focus to appear out of focus. Even at 50% either way, things may start to look unsharp.

In fact, this exactly matches what I saw in my recent attempt a couple of days ago. It took me a couple of tries to realize the arc being made during focusing and recomposing would make a difference at that level.

Thanks, my old bridge camera did not have any other focus points so had to do this and I hoped it didnt make much difference but it didnt allways produce sharp shots anyway. Much hapier now with an SLR again.

On a related note, my left eye is better than my right so I tend to use that which puts my nose on the focus point select D-Pad not making the easiest to use.

you got me thinking with this subject....
I noticed that when I shoot and recompose, I do not tilt or swing my camera around at all....I tend to move my body by stepping side to side, and bend at the kneees when recomosing. It would seem that I've been instinctually keeping my camera parallel and level, and maintaining an accurate distance even when recomposing.

the effect described in the text might come into play, if one recomposed by tilting or swinging the camera while fixed on a tripod, essentially you'd have to refocus because you changed your camera angle. How much leeway you get would matter if your dof was very shallow....