Archived posting to the Leica Users Group, 2001/02/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Austin Franklin jotted down the following: >> >> http://www.silverlight.co.uk/resources/dof_calc.html >> >>> From: "Austin Franklin" <austin@darkroom.com> >>> >>>> Wide open and focused close, the depth of field of the 75/1.4 >>>> is between 6mm >>>> to 8mm (just over a quarter inch). >>> >>> What are you basing this number on? > > I don't believe it's accurate. I routinely shoot at 1.4 with both a 75 and > an 85, and I find my critical DOF to be much much larger than 6mm to 8mm. I > also print typically 13x19...so DOF is quite noticeable. Again, DOF is a perceptual effect, not a physical property of the world. It is based upon the perceived zone of sharpness around the plane in focus and, as such, is affected by how good your vision is, how large is the print, and the viewing distance from that print. 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. - -- Martin Howard | "We can't make mistakes like that on our Visiting Scholar, CSEL, OSU | own. We need computers to help us." email: howard.390@osu.edu | -- A pharmacologist on computerization www: http://mvhoward.i.am/ +-------------------------------------------