No that means it would need an 80mm aperture, if it is actually a 2.5. The front element can be slightly smaller on an extreme telephoto design, just as it needs to be a lot bigger than the aperture on an extreme retrofocus design lens.
--graywolf ------------------------------------------------- The optimist's cup is half full, The pessimist's is half empty, The wise man enjoys his drink. ----- Original Message ----- From: Frank Wajer <[EMAIL PROTECTED]> To: pdml <[EMAIL PROTECTED]> Sent: Friday, November 09, 2001 5:30 AM Subject: 200 f2.5 question, how can filter ring be 77mm? > Hi, > > on kmp.bdimitrov.de I saw the specs of the 200 f2.5 lens. It says that the > filter > ring is 77mm, but this means that the lens cannot be f2.5, as that would > mean > a minimum 80mm filter ring! > > Can anyone explain? > > > BTW. Isn't it save to have some margin between the filter ring and what is > calculated by dividing the focal length and the aperture. I'm thinking > about > robustness against vignetting, especially when using a filter. > > Frank > - > This message is from the Pentax-Discuss Mail List. To unsubscribe, > go to http://www.pdml.net and follow the directions. Don't forget to > visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
