Originally posted by osv contrast that with the o.p., reh, etc., who want to take one semi-measured focus point only, throw some sloppy unmeasured dof at it, and then take multiple photos, without re-focusing on objects that have moved within the dof region.
No! No! No!
I never said anything about taking multiple shots.
The issue is getting just one shot of a moving subject.
Here are several scenarios that involve taking just one picture, but a deep assured DOF is needed, and there is no way to use LiveView or "chimping" to provide that assurance:
(1) I already described taking pictures of my daughter playing basketball. That description had nothing to do with taking multiple pictures .... I was trying to get just one picture of her, using an MF lens. Keeping her in focus by moving me was not a viable option, because I was in a gym with rows of seats and various steel railings that limited mobility. Since she would not stay put long enough for me to focus on her, I had to draw a DOF box around her, so I knew if she stayed in a certain region she would be "in acceptable focus". That is not perfect, but it is better than nothing.
(2) I take pictures of wildlife Often the animal will start to leave just after I have focused on it. Take the picture now, or never, because most likely it won't come back. An appropriate DOF assures that the {one} picture taken just after it has started to move will be essentially as good as the {one} picture that wasn't taken just before it started to move. The entire process doesn't leave sufficient time to use LiveView or "chimping" to evaluate DOF
(3) Sometimes I visit Indianapolis Motor Speedway. Cars come around the corners at high speed; you can hear the car coming, but either you cannot see it at all, or your view is insufficient to tell which "line" it is following. I don't know until the car actually arrives whether it is following the specific line I had focused for, leaving insufficient time to move to maintain current focus or to refocus, even if I could determine what changes need to be made. They keep the track clean and smooth, so there is very little to use for evaluating focus in advance using LiveView or chimping, but an appropriate DOF assures that the car will be "in acceptable focus" regardless of which line it is following.
(4) You take pictures of drag racers; I take pictures of trains. Your pictures appear to be taken roughly perpendicular to the vehicle, so virtually everything is close to the plane of focus. My pictures are often taken at 30- 45 degrees away from perpendicular; an 80' passenger car or locomotive will extend nearly 30' on either side of the plane of focus, so I need significant and assured DOF to get the entire object in acceptable focus in the {one} picture I take.
---------- Post added 04-20-16 at 10:42 AM ----------
Originally posted by osv "A camera lens can only focus on one plane of the subject. This is the only area of the scene that is really sharp."
Depth-of-field - Canon Professional Network
there is no doubt that a sharp plane of focus can be seen... i don't get how you could think otherwise.
I haven't seen anyone here doubt that a plane of focus exists. The issue is that you keep insisting that it is a physical entity, and at times have acted as though it has actual depth. It is a reference entity, like a longitude marking. It is a mathematical construct, the locus of points a certain distance away, and being a mathematical plane, it has two dimensions, height and width, only. It has no meaningful depth - you are into DOF as soon as you are any measurable distance from it.