I suppose the list is getting tired of this, so via direct e-mail. (Oops! apparently, your ISP has my ISP blocked, so posting to the list after all).
I am going to have to do some re-research to figure out exactly how I came to the original conclusions. Which means a trip to the library. The problem being that there are almost as many formulas for DOF on the internet as there are internet sites. I need to go back to a basic optical physics book. In other words now I am confused. Thinking did not used to confuse me <SIGH>. See other comments inline: Ciao, Graywolf http://pages.prodigy.net/graywolfphoto ----- Original Message ----- From: "Mike Ignatiev" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, July 25, 2003 3:17 PM Subject: Re: Shallow DOF with 6X7 lenses > I think this is a really good version of the formula, > especially, if you write it as > Dn = h/(h+l), Df = h/(h-l) when h>l Dn = hs/(h+s), Df = hs/(h-s) Is what that book gives. What would you get if h>1? And, why would you want to focus beyond infinity? > > However, in the definition of what h (hyperfocal distance is) the "1000" factor should really depend on the final enlargement. Do you insist that h would be > the same for 4x6 print and 40x60 alike? > > One (also approximate) definition of h is > > h = d*f/c, where c -- COC, f -- focal length, > d -- actual aperture diameter. > Your "1000" means f/c = 1000. > This is interesting, and it means that as you change > the film format (say, double both f and c), as long as > you keep the enlargments of the same size, the hyperfocal distance does not change. And neither does > DOF. Yes! Or, your enlargement is viewed at a distance where the perspective matchs that of the original scene. > > Btw, your formula does not prove your point -- > you express it through diameter and distance-to- > subject. Not magnification and COC <G>. > No, becomes a fixed value, because it is the same for the final print. The formula is somewhat specialized. BTW, I think now precive why the formula Mark quoted did not work for me. I was trying to use it as a general formula and it is specific to magnifications near to 1. But, why did I get values that seemed correct for farther distances when I used aperture rather than f-stop? I shall have to run some numbers, and see if I can figure that out. I wish I could find the book that gave that formula (or what I remember being the same formula), but I probably do not have it anymore. I am sure it was a general photography book, not one for close-up photography though. > But of course, all these things are related > geometrically. Yes, we kids do know it all <VBG> > Or, at least your math skills are fresher. I will admit, that it gets harder as I age, and use them less an less <NSVBG>. But, I do good for a 10th grade dropout.
