Archived posting to the Leica Users Group, 1999/07/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Any distance other than the plane of focus is going to be out of focus. The near and far ranges of the DOF are supposed to be the minimum and maximum distances for which objects will not be so out of focus that it will be obvious on a 8 x 10 print viewed at a certain distance (I forget how far that's supposed to be). The DOF formulas depend on the size of the circle of confusion, which is a measure of how out of focus something is. It is purely optical theory and doesn't take into account lens characteristics. Theoretically, a perfect mathematical point which is out of focus will produce an image which is a disc, or circle, rather than a point. The diameter of this disc is the circle of confusion (COC). The largest allowable COC determines what is known as "acceptable" focus. The smaller the allowable circle of confusion, the sharper the acceptable focus. Zeiss seems to favor 0.025mm, while Leica seems to use 0.033mm. Using a smaller COC in the DOF formulas results in a shallower DOF. The COC is merely a way of making the idea of "acceptable" focus mathematically precise. What COC to use in the formulas depends on the size of the enlargements you wish to make, the viewing distance, the prominence of the film grain, etc.There are so many variables that it's hardly worth bothering with. Richard S. Date sent: Thu, 8 Jul 1999 12:10:53 +0200 To: leica-users@mejac.palo-alto.ca.us From: Mikiro Mori <arbos@silva.net> Subject: [Leica] DOF? Send reply to: leica-users@mejac.palo-alto.ca.us > Hi, I have a beginner's question. What is a definition of DOF? I assume > that a plane of focus has no depth or thickness and that resolution/contrast > is a function of the distance from the plane.... Such functions should > depend on lens design and may explain lens characters.... If so, DOFs > calculated with a single formula have limited significance in real shooting. > Could someone please enlighten me. > > Cheers, > > Mikiro > > >