Afyer 35 years of experience, I dont need no stinking formula, everybody knows the depth of field is image locked once you make the exposure. To change it ( increase or decrease the relative depth of field ), you have to change the in-camera magnification or fstop before shooting. You cant manipulate more or less image DOF ***after the exposure ***. Making a print larger or smaller doesnt change DOF, nor does declaring a the COC bigger or larger. To increase or decrease the image DOF you have make changes BEFORE the exposure....AFTER is impossible.
While not a formula, its a rule, DOF is proportional to f-number and inversely proportional to in-camera image magnification. Relative DOF = (f-stop number)/(in camera image magnification). These are the only two factors that increase or decrease relative DOF. These cannot be changed after the exposure. NOTE how, COC, Format, focal length, print size, etc do not matter. ONLY in-camera magnification changes and/or f-ratio changes can increase or decrease the relative DOF. Its very basic. JC O'Connell hifis...@gate.net -----Original Message----- From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of Bob W Sent: Tuesday, April 07, 2009 4:03 AM To: 'Pentax-Discuss Mail List' Subject: RE: Trading resolution for depth of field 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 > hifis...@gate.net > > > > 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 > > hifis...@gate.net > > > > > > > > -----Original Message----- > > From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] 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 PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions. -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
