Topic: The dreaded DoF issue again (Read 6475 times)

howard smith · « **Reply #20 on:** July 21, 2005, 02:34:08 pm »

"... format (size and resolution?)... "

Resolution has nothing to do with format. Format is simply the length and height of the recording medium.. Format is sometimes "shorthanded" to 35mm, for example, to mean 24x36mm. For a "full frame digital" camera, the number or kind of pixels matters not.

"If you think that the size of the range of acceptable sharpeness is NOT the same in both of these large prints, then I think you would conclude that format has an impact?"

To refine the arguement a bit, a "fuzzy" (soft) print may actually appear to have more DoF, all else being equal, than a sharper print. It is more difficult to detect the CoC on a fuzzt print.

Well, Tim, you would be wrong. The DoF on the prints is different, because the degree of enlargement is different, not because the camera formats were different. Surely you aren't trying to tell me that for the camera's format will always tell me the degree of enlargement?

Jonathan Wienke · « **Reply #21 on:** July 21, 2005, 08:45:15 pm »

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It's easy to get information on the pixel pitch of your camera's sensor, so making the CoC equal to the pixel pitch is a way out, but doesn't seem to me entirely satisfactory.

Perhaps not, but at least it's something that accurately predicts DOF for prints ranging from 5x7 to 24x36 (which covers the range of sizes I offer for sale), and gives me something consistent to work with while shooting. What's the downside?

Ray · « **Reply #22 on:** July 21, 2005, 10:41:26 pm »

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What's the downside?

Using an unnecessarily small aperture and slow shutter speed to gain an unecessary degree of DoF for a particular print size?

Ray · « **Reply #23 on:** July 22, 2005, 03:44:50 am »

Bernard,
There's a much more benign way than that. You lead the elephant to a placid lake with a pebbled beach. Coax it onto a barge. Mark the level to which the barge sinks. Get the elephant off the barge. Gradually fill up the barge with pebbles, weighing each pebble first and recording the weight, until the barge sinks to the same level.

This is the Chinese version of the Archimedes' principle. It's also Howard's version of DoF calculation without knowledge of format.

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