Instead of making an unsupported assertion why don't you provide a formula for calculating depth of field? Then we will all be able to test your assertion.
I have provided a formula which shows quite clearly that you are wrong. The calculation uses coc as a factor. The formula for coc depends on viewing distance and print size, therefore by changing either of these the coc changes. If the coc changes, the depth of field changes. You can't argue with the numbers. Give us a formula which shows you are right, then people might start to take you seriously. Jose > > NO WAY JOSE. you can never change the dof > after the shot, DOF is an "in camera" thingy... > you have to change the in camera image magnification or > f-stop to change the image DOF. > > JC O'Connell > [email protected] > > > > Coc is always a factor. > > You can change the viewing distance or the print size, and > the depth of > field changes. > > Bob > > > > > The question was regarding relative DOF, COC is not > > a factor. The only way to increase DOF from whatever > > your reference is, is to decrease IN CAMERA magnification > > or increase f-stop number. All that other stuff is moot. > > You cant change the relative DOF of an image after you > > shoot it. > > > > JC O'Connell > > [email protected] > > > > > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] On > > Behalf Of > > Larry Colen > > Sent: Monday, April 06, 2009 5:47 PM > > To: Pentax-Discuss Mail List > > Subject: Re: Trading resolution for depth of field > > > > > > On Mon, Apr 06, 2009 at 10:32:37PM +0100, Bob W wrote: > > > > So, if I'm willing to trade resolution for depth of field, am I > > > > better off using a wider angle lens and cropping (my > > intuition says > > > > yes), or do I get the same benefit by just combining > > pixels (which > > > > would also reduce noise) for a larger circle of confusion? > > > > > > > > > > To calculate the nearest (dn) and furthest (df) points in > focus use > > > the following formulae: > > > > > > dn = U * F^2 / [F^2 + (U * c * f)] > > > df = U * F^2 / [F^2 - (U * c * f)] > > > > Ah. Thanks. Focal length is second order factor, circle of > > confusion is > > first order, so focal length has a greater effect on DOF, than CoC > > (pixel size). > > > > > > > > where > > > c = circle of confusion > > > U = subject distance > > > F = focal length > > > f = f-number > > > > > > To calculate the circle of confusion > > > > > > c = (v * D) / (1000 * S) > > > > > > where > > > v = film format / image size > > > D = viewing distance > > > S = print size > > > > > > Source: The Professional Guide to Photo Data, 3rd edition, > > by Richard > > > Platt. > > > > > > Very easy with a spreadsheet. > > > > > > Bob -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
