Archived posting to the Leica Users Group, 1997/08/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]How can this be????????? > >My real world experience tells me this Mamiya 35C doesn't deliver sharp >images period. Someone at Mamiya had to be playing with those circle >of diffusion numbers to show that the Mamiya has more "depth of field". > Anyhow, if I'm shooting at f/16 I usually set the infinity mark to >around f/8 as a safety margin and sometimes bracket focus if it's >really critical. > >Theory is fine, but doesn't always play out in practice. Sorry, I >don't have equivalent Leica lenses to compare yet. > >Duane Birkey >HCJB World Radio >Quito Ecuador > You got it!!!, the DOF are based on different circles of confusion. Not only that but your DOF for a given lens and format will vary depending on big you enlarge. I.e., a contact print will have more DOF than a 40 x 60 inch (1 x 1.5 m) print!!! So if you want bigger blow-ups use the DOF marks for a larger aperture than the one you are actually shooting. Since med. format negs are not blown up as much, DOF can be based on arger COC, hence your observation. If you blow up two negs shot with the same focal length but different sized negatives the same amount, e.g., 10X, the DOF will be about the same. The "about" is used above instead of "exactly" because of pupilary magnification effects, but that is another story! Tom Thomas C. Kline, Jr., Ph.D. Research Scientist/ Diving Safety Officer Prince William Sound Science Center 300 Breakwater Avenue, P. O. Box 705 Cordova, AK 99574, USA 907-424-5800 tkline@grizzly.pwssc.gen.ak.us http://www.pwssc.gen.ak.us/