Focus Point Questions

Letting the camera choose your focus point will likely result in more times when the camera doesn't focus on the point you want to focus on. I always select the specific focus point I want to use and minimize any focus/recomposition issues.

Thanks.. that what I thought.... I've had this nagging feeling though that all points focusing might affect DOF somewhat in how the camera determines shutter/aperature in Program mode... just a thought.

Centre mostly, but commonly just use the one closest to the main subject or part of subject most important.

Usually the center point.

Automatic Focus Point Selection behaves differently between OneShot and AIServo. I would never think of using AFPS in OneShot mode because the camera is going to determine what AF point it's going to use and you have no control over that.

However, in AIServo mode, the AF acquisition always starts with the center AF point and remains there unless the target moves off the center AF point. Then, the camera tracks the target with the one of the other AF points if the target is covered by any of the other AF points. There are times when I do use AFPS in AIServo mode when shooting birds in flight.

I'm always changing my focus point... I love the 40D for this reason.... just push the button, spin the wheel and you focus where you want to, not where the camera does.

In the rare circumstances where I do want all the focus points, I just switch to A-DEP cause that's what I'm after.

I use manual FP selection, and I use the multi-controller to select them. It is clearly the quickest and most efficient way to control the AF.

I don't track moving subjects much so I haven't tried auto selection in AI Servo.

When I first got my XSi, used all the points.

You can get the hang of that, and as long as you pay attention to what is getting focus lock, it can be effective. But sometimes frustrating. Success once trained: 80% in focus

Then I used center point. Learned the DOF make a difference in DSLR when focus and recompose. Without recomposing, shots became boring - main subject always in center with lots of sky above head to get her eyes at the center focus point. Success 80 in focus (and still did some recomposing)

Live mode trial. inanimate objects 100% focus. Moving objects - object not technically out of focus, they just aren't in the frame any more. Live focus very effective for stationary objects (portraits, landscape), less helpul when used as a digicam.

The best method is to become very quick at selecting the ponit at your subject. It is a 9 point pattern so easy to memorize, and button pushing without looking will quickly develop. Ideally focus point right at eyes of main subject. Success 95% in focus

I use center point exclusively with oneshot. Haven't ventured into AIServo much.
I wish there was a easier on the fly method to changing the focal point though on the XTI.
I realize there is the Cf selection but then I lose use of the ISO and metering functions.

m-bartelt wrote in post #6036388
I'm always changing my focus point... I love the 40D for this reason.... just push the button, spin the wheel and you focus where you want to, not where the camera does.

In the rare circumstances where I do want all the focus points, I just switch to A-DEP cause that's what I'm after.

change it so that you use the multi-controller to control which AF point. You will love this even more that a press+wheel spin method. One touch in the direction of the point and that is the one you will use.

Nelson

I went to a clinic recently given by a well known nature photographer. He described using all focus points as the Canon circle of failure. I have to agree. My camera seems to inevitably set the point on something I don't want in focus.

Consider this...the classic film SLR of 30 years ago had a focus aid in the center of the frame to help with precision focusing. The photographer manually focuses, then recomposes the frame for good composition, then shoots. Now simply apply that usage model to the modern dSLR, and you have a very workable solution.

Yet many photographers will challenge, "But what about the focus shift caused by focus-recompose?!" The response is, usually the DOF of the lens at the shooting aperture will more than compensate for the plane-of-focus shift which occurs, unless you are at very close distances at wide open aperture. In general, the DOF will compensate if the angular shift is under 20 degrees (outside the visible frame on a telephoto FL!) even with wide open aperture. Yes, using manual focus point selection initially, rather than the center AF point, would reduce the issue of focus-recompose, but I am merely pointing out the issue is not as dire as some would lead you to believe...after all, decades of film photographers coped, and they had the lesser DOF of 135 format and medium format SLRs to cope with!

I almost always use the centre point for static subjects except situations that would result in a shift of the point of sharp focus away from the intended distance with narrow DOF. I don't do much of that kind of shooting, though.

With sports subjects, I mix between the centre point and all points depending upon the subject. Where all-points comes into its own is a reasonably flat subject that has a lot of large gaps in it. In other words, a cyclist passing your position. If a single point falls into one of the gaps, it just locks onto the background and wrecks the shot, but the all-points mode does a very good job of maintaining a lock on the bike/rider on the nearest point of good contrast without needing to compromise the composition. I get good results from that, while a single point fails too often. However, all-points is not very good at dealing with a subject that provides appreciably different planes of focus, which tends to produce a potentially unacceptable degree of inconsistency unless the DOF is deep.

Wilt wrote in post #6037048
Consider this...the classic film SLR of 30 years ago had a focus aid in the center of the frame to help with precision focusing. The photographer manually focuses, then recomposes the frame for good composition, then shoots. Now simply apply that usage model to the modern dSLR, and you have a very workable solution.

Yet many photographers will challenge, "But what about the focus shift caused by focus-recompose?!" The response is, usually the DOF of the lens at the shooting aperture will more than compensate for the plane-of-focus shift which occurs, unless you are at very close distances at wide open aperture. In general, the DOF will compensate if the angular shift is under 20 degrees (outside the visible frame on a telephoto FL!) even with wide open aperture. Yes, using manual focus point selection initially, rather than the center AF point, would reduce the issue of focus-recompose, but I am merely pointing out the issue is not as dire as some would lead you to believe...after all, decades of film photographers coped, and they had the lesser DOF of 135 format and medium format SLRs to cope with!

So, are you saying that you manually focus your lens instead of using AF?