Steven, It does not matter which equipment you use. The DOF is a function of (roughly) (1) magnification (M) (2) focal length (f) -- weakly (3) aperture (N) (4) acceptable circle of confusion (c)
and it (changing one parameter at a time) increases with aperture and (insignificantly) focal length and decreases with magnification. DOF ~ N*(1+M)*c/(M^2*(1 +or- (N*c)/(f*M))) ~ N*(1+M)*c/M^2 + or - depends on whether it is front or rear DOF. 0.03mm is a good number for c, M is ~ 0.2 in your case, so this gives you DOF = 0.9N (mm). A few mm DOF means N is < 8. I don't think any special macro equipment is needed for this purpose, an extension tube + a prime or any macro zoom should be OK. Hope it helps, Mishka > From: steven gilson > Subject: OT: limiting DOF for macro??? > Date: Thu, 23 May 2002 11:44:12 -0700 > -------- > > I need advice on how to severly limit DOF for macro work. I realize > that most (all?) macro equipment tends to reduce DOF. I want to > limit the sharp area to a few millimeters on a (35mm) frame filling > shot of a 5 inch subject. What is the best set up for this? Tubes, > reversing ring, close-up filters, dedicated macro lens? > > I have no true macro equipment now so I will be buying whatever it is > that I need so cost is a factor. I do have a 35-105/3.5 and 80- > 200/4 "macro" zooms plus 28/2.8, 50/1.4, 135/3.5 and 200/3.5 primes > if any of these can be worked to the set up. > Thanks in advance for all replies > Steven. LAUNCH - Your Yahoo! Music Experience http://launch.yahoo.com - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
