Can someone explain why one must pay such a penalty in filter size when buying a short or mid-length constant-aperture zoom?
At the wide end, it's not uncommon for a 28-70/2.8 zoom, say, to use a 72mm filter. Yet the 28/2.8 and 77/1.8 can use a 49mm filter. The Rikenon 28-100/4 requires a 67mm filter. Yet a 28/4 or 100/4 can use a 49 or 52mm filter. As for the 28-135/4, its 77mm filter size simply dwarfs any f/4 prime in its focal range. For telezooms, there doesn't seem to be such a penalty. A 200/2.8 uses a 67 to 77mm filter. An 80-200/2.8 zoom typically uses a 72 or 77mm. What explains why short to mid zooms must be so much wider in front than the primes in their range, but not long zooms? [EMAIL PROTECTED] -------------------------------------------------------------------- mail2web - Check your email from the web at http://mail2web.com/ . - 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 .
