Archived posting to the Leica Users Group, 2001/02/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Martin Howard wrote: ><Snip> > When DOF is calculated, it is based upon normal viewing distance (I forget > exactly what this is) of an 8x10" print and the "normal" human actuity of > 0.2mm, which translates into circles of confusion in the 35mm negative of > 0.03mm. > > It's a guideline. Not an absolute. YMMV. In fact, it's almost guaranteed > to do that. Much like exposure metering in that way. > > M. > Aha! the only math thing i know is viewing distance! a 50mm lens is two inches long. 35mm film is one inch on the short side. If you make a 6x9 image that is a six times magnification. 6 (mag) x 2 (focal length) = 12 inches (viewing distance). So hold up your print exactly a foot from you eyes and see if it glitches to all its wonderfulness. I kind of like to do that sometimes. A 24mm lens is one inch so hold the print 6 inches away then and see how the perspective looks just right! You've got to climb right in there! A 9 inch mag on a 11x14 print shot with a 90 is 3.5433 x 9 is 32 inches away!! so stand back almost a yard from the wall and get a proper perspective on that print. you've got room to stand and look at a print with those numbers working for you. 11x14's are definitely wall size, if not 16x20's if you are not using long lenses. markrabiner