On 7/13/06, Mark Roberts <[EMAIL PROTECTED]> wrote: > Perry Pellechia wrote: > > >> >Unusual length for 35mm. > >> > >> Yeah, they should have made it 77mm :) > > > >This comment reminds me of a question I always had about the > >Limited's. I know the reason for the 43mm focal length (true normal), > >but what is significant about 31mm and 77mm? Anyone know? > > > Well the word is that there really isn't anything special about the > numbers 31 and 77, it's just that most lenses, from all manufacturers, > aren't named with their actual focal length but with the "standard" > number that's closest. In other words, a "100mm" lens might actually > be anywhere from 95mm to 104mm, but gets the "100" designation just to > make it easier to remember. Sometimes lens tests will list the actual > measured focal length as well as the designated focal length. > > With the 31 Ltd and 77 Ltd, Pentax apparently just gave the lenses > names that were indicative of their actual focal length. An unromantic > explanation, I realize, but what can you do? :) >
Thanks for the explanation Mark. I guess the next question would be how were these lenses designed. Were the shooting for 30mm and ended up with a 31mm? I would have thought that they would have been designed using some sort of computer system and the mathematics would have been more precise. My guess would be the differences being introduced by material changes (glass type and refractive index changes, etc.) -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
