Archived posting to the Leica Users Group, 1998/04/21
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Duncan wrote: > A > | > | > | > | > | > | >Camera >----------------------B ---- center of view ( .i.e. camera is aimed > at B ) > > >Distancace to A and B from the camera are different, but if the camera has a >flat field, then both will be in focus. If one recomposes to put A in the >center of the field and B on the edge, then A will behind the plane of focus >and B will be in front. You are correct but that is not the question. The question is if you focus on A and then recompose to B (without refocusing) then, if you assume a flat field, A would be past the point of focus and B would be in front of the point of focus. Because, assuming a flat field the point of focus is closer to the center than it would be to the 2 edges. If you focused a 35 mm lens to 10 feet it is only 10 feet in the middle. The distance to the 2 edges is 11 1/4 feet. If you were to take a picture of a brick building from the middle of the one sides, you know the building is closest to you straigt ahead and it is further away from you to the 2 corners. You depend on a lens's flatness of field and D.O.F. to get the whole building in sharp focus, even though it is farther to the 2 corners. I would bet that lenses flatness of field is somewhere inbetween. In other words you get some curving from the central point of focus. This would help compensate for both situations to some degree. I would further bet that it is only a problem with medium wide angle and "normal" lenses. I would think super wides have to great a D.O.F. and teles have to narrow an angle of view. What can I say to get you guys to think about this. Well, let's see! The first paragraph is math and not subject to interpretation. It just is fact. The second paragraph is my opinion. Art Art Searle, W2NRA, w2nra@erols.com, Lake Grove, Long Island, NY, USA 20 miles east of Nikon USA, 70 miles east of Leica USA