Your post concurs with mine as I have previously stated the same thing, what you are calling the point of critical focus is what I am talking about all along. jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Paul Stenquist Sent: Tuesday, November 14, 2006 4:08 PM To: Pentax-Discuss Mail List Subject: Re: Using a Super Tak w/ istDS- A challange to the list? I think party of the confusion here is in regard to what constitutes critical focus and what might fall within the depth of field of a given lens. Every lens, no matter how wide has only one point of critical focus. With my DA 12-24 at 12mm that point is nearly impossible to find. Almost everything appears to be in focus. So one could say that it's very easy to focus the 12mm lens. Yet there is a point of critical focus. For important work, I try to locate that critical point exactly where I want it. Sometimes I have to resort to the distance scale to achieve critical focus with this wide a lens. On the other hand, with my 400mm lens, it's easy to see what is in focus and what is not due to the lack of depth of field. On Nov 14, 2006, at 3:35 PM, J. C. O'Connell wrote: > I say its EASIER to focus longer lenses > with the same accuracy at same fstop/speed, all > else being equal. > jco > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of > Cory Papenfuss > Sent: Tuesday, November 14, 2006 2:46 PM > To: Pentax-Discuss Mail List > Subject: Re: Using a Super Tak w/ istDS- A challange to the list? > > >> So, how does one measure ease of focusing in a lab? How does one >> measure comparative ease of focusing (say a 35mm lens v a 105mm >> lens)? > >> What tests are used, what equipment is used? How do you define >> "ease?" Is the lens tested on a camera, or is the camera something >> that gets in the way of an objective test? Is there an "easy of >> focusing" machine to which the lens is attached? Do you use more >> than > >> one sample of each lens? Do you change the light at times, vary the >> subject? Is there an "ease of focusing" test target? How does the >> target relate to real world subjects? For example, does the lab >> target have a face? A nose? Eyes? Wear glasses? Or is it some >> flat > >> sheet of paper with grid lines on it? >> >> Shel >> >> > Again... I believe I was careful not to say, "ease," but rather > "accuracy." The latter can be objectively measured and quantified and > the > former will always be run through an individuals' personal > preferences. > > -Cory > > -- > > ********************************************************************** > ** > * > * Cory Papenfuss, Ph.D., PPSEL-IA > * > * Electrical Engineering > * > * Virginia Polytechnic Institute and State University > * > ********************************************************************** > ** > * > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
