>>Re: My own DOF confusion >Date: Mon, 22 Mar 2004 13:39:29 +0300 >From: "Boris Liberman" <[EMAIL PROTECTED]> >To: "PDML" <[EMAIL PROTECTED]> > >Hello. > >Few days ago I received my own pancake lens. This is probably the >cheapest one - Industar 50-2 (50mm f/3.5) lens. I've been told that >being relatively slow and being based on classic Tessar formula, it >should be reasonably good optic... > >Anyway... I've compared the readings of DOF scale of this lens and my >M 50/2.0. Thankfully, it has proper DOF scale unlike modern FA 50/1.7 >that I also have. Industar has considerably bigger (right term?) DOF >for the same aperture. I cannot give the exact numbers, as I am in my >office. > >Nonetheless, I am confused - how can that be? I've been told that if >the lens has less elements (Industar is 4 lenses in 3 groups, if I am >not mistaken), then it presumably should have a bigger DOF. > >Please help me out on this one. > >Confused in Tel Aviv. > >Boris
Dear Confused, Each optical formula affects the dimension of the "circle of confusion" in its own way. And while they may be very close, they're all different. This can even be see in in the finder! The Pentax-A 70-210/4 and the Takumar-A 70-200/4 present the results very differently, even in the finder of a small Pentax body. Just because the focal length is the same does not mean that the behavior is necessarily the same. The loss sustained with standard lens designs for 35mm outfits is something to get used to when going to medium- and large-format designs. Using a Tessar design may provide a better image perspective and you may be either pleased or disapppointed with what you see -- depending on your familiarity with larger formats. The Tessar design has been used on many TLR cameras because of it's compactness. Personally, I'd like to try one just to see how it behaves. Collin
