NO I DISAGREE. Image DOF is the RELATIVE sharpness of objects in front of, and behind, the actual plane of focus. TO INCREASE OR DECREASE this relative sharpness you have to change the incamera magnification or f-stop. PRINT SIZE has nothing to do with changing the DOF of an image. While you can argue all day long that making a print smaller and smaller increases the "perceived" DOF, I dont, because all it does is make it harder to see the **same DOF**, its doesnt actually change the image DOF at all.
Furthermore, I disagree with using the term "critial" to define DOF. Its not critical, its what it is, and thats simply the difference in sharpness of foreground and background objects relative to objects in the plane of focus. It doesnt have to be some "critical" barely perceivable difference, sometimes its huge and obvious. but in any case, if you want to increase or decrease that DOF, you need to know what CHANGES it, and what DOES NOT. JC O'Connell [email protected] -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Paul Stenquist Sent: Tuesday, April 07, 2009 8:35 AM To: Pentax-Discuss Mail List Subject: Re: Trading resolution for depth of field This is a simple issue. Bob is speaking of perceived depth of filed on a viewed print. JCO is speaking of critical depth of field in respect to the ability of a given lens to resolve detail. Both are correct, but each is discussing an entirely different matter. Let it go. On Apr 7, 2009, at 4:02 AM, Bob W wrote: > 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. -- 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. -- 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.
