Clearly you can (within reason) decouple the size of the glass and the image circle. That's not what this debate is about... this is about the resulting _brightness_ of the image circle.
If you reduce the size of the image circle, you get a brighter image. For those of you who doubt this, I refer you to adolescent experiments in starting fires with a magnifying glass - image circle size does matter! :-) Image brightness is some function of the size of the size of the gathering end to the size of the image circle. This is the basic reason lenses for smaller sensors are smaller for the same speed as a full-frame lens... they are not throwing as many photons away. -Bob -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Henning Wulff Sent: Saturday, December 02, 2006 9:43 PM To: [email protected] Subject: Re: EOS re 1.6X telephoto >On Fri, 1 Dec 2006 15:36:46 -0800, Henning Wulff <[EMAIL PROTECTED]> >wrote/replied to: > >>>You'll never convince me though that if the optical circle doesn't >>>need to be so >>>big, that the glass lenses used can't all be a bit smaller. Why do you think >>>medium format lenses are all so fat? >> >>Because for the most part they're made with different criteria in >>mind. Manufacturers know that people buy (bought) MF equipment for >>high quality, so everything about the systems was optimized in that >>direction. Weight and size were not the main concerns. Durability, >>high sync shutter-in-lens are things of importance. > >Yes, and the Sigma made for smaller sensors is made with different criteria in >mind, that's my point. It's made for someone who wants a thinner, >lighter lens. >That is the design objective they start off with and I guess they >manage to trim >it down considerably. Otherwise nobody would buy it. > >We haven't touched the optical laws of physics here though, about making a >bigger image circle. I guarantee you it requires bigger glass not smaller and >vice versa. > >-- >Jim Davis, Owner, Eastern Beaver Company: >http://easternbeaver.com/ Motorcycle Relay Kits, >Modulator Kits, Powerlet, Centech, Posi-Lock, Parts. >1988 K100RS SE ABS in Japan. 1991 ST1100 in America. >STOC#6327, IBMWR, KBMW >* >**** Image circle and size of glass are not interdependent. Look it up since you clearly don't believe me. -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.430 / Virus Database: 268.15.6/565 - Release Date: 12/2/2006 9:39 PM * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
