Dear PFers, About to make a decision about which flavor of EF 70-200/2.8 L lens to buy... Pl. put in your inputs about practical problems/likings about IS versus non-IS version. Is it really needed and how much do you use it if you have IS (I don't do much panning or sports but can not in dimly lit lanes where t can be as low as 1/15 sec. wide open). There is a lot of price difference in these two versions, so I really want to hear pros/cons before buying. f4 version is out of question since I really need more light. what are practical limitations about carrying this lens (because of weight), do you use monopod with this one? thanks comments, achal PS: sold 4X5 after moderate use, it was really not my cup of tea/coffee. It was too heavy and too impractical to carry around with its heavier tripod! :( Achal Pashine Pediatric Immunology Center for Clinical Sciences Research, Room 2120 269 Campus Drive Stanford, CA 94305-5164 Tel: 1-650-498-7574 FAX: 1-650-498-6077 ----- Original Message ----- From: "Richard Martin" <marphoto@yahoo.com> To: "List for Photo/Imaging Educators - Professionals - Students" <photoforum@ase-listmail.rit.edu> Sent: Thursday, August 22, 2002 4:54 PM Subject: Re: Lens Query > --- Don Feinberg <donf@cybernex.net> wrote: > > > ....The small end stop becomes smaller by the same factor as > the > > large-end stop > > (as do all the numerical apertures; the lens mfr expects the > > camera's meter > > to compensate. > > > > So, assume a 100 to 300mm f/3.5 to 5.6 zoom which has a > > diaphragm > > numerically scaled from f/3.5 to f/22 -- very typical. These > > lenses tend to > > test out at f/4 to f/6.3 in the real world. At the 300 end, > > instead of > > f/22, the aperture will be closer to about f/37 to f/45. (You > > can calculate > > for yourself the diffraction effects...) Of course, Joe > > VacationPhotographer will be blithely using the lens stopped > > down to try to > > increase "depth of field"... Not nice! > > > > You raise some interesting points. I've long known that the > actual apertures of lenses is often somewhat different from the > "published" ones. But I have 3 questions. > > 1. How would an individual, without any formal technical > training, actually test this with a particular lens? > > 2. How did you arrive at the values "f/37 to f/45" minimum > aperture from an actual f/6.3 maximum aperture? > > 3. How would one "calculate for diffraction"? > > Math is not my strong suit but I'll try to absorb any > explanation you care to offer. This subject (variable f/stops) > has long intrigued me. > > Richard > > > > > ===== > Richard Martin specializes in Cityscape and Waterscape stock photography as well as Children's Portraiture. E-mail: marphoto@yahoo.com > > __________________________________________________ > Do You Yahoo!? > HotJobs - Search Thousands of New Jobs > http://www.hotjobs.com >
