On Wed, Mar 08, 2006 at 05:01:30PM -0700, Tom C wrote: > >From: Joseph Tainter <[EMAIL PROTECTED]> > >At B&H the Hoya RM 72 costs as follows: > > > >67 mm: $ 80.95 > >77 mm: $283.50 > > > >Hard to figure why the 77 would be so much more. A 77 would be logical for > >me. It would fit my DA 14, and with step-up rings, every other lens. It > >would also fit the forthcoming DA 16-50 F2.8, which I would guess will > >have a 77 mm. filter thread. But, oh, the price! > > > >Joe > > > > That's easy. > The 77mm has to block 13% more infrared photons as the 67mm version.
<NITPICK> I think you mean 32% more photons? (I don't know where you got 13% from - even using linear scaling, 77mm comes to 15% more than 67mm. Area, of course, is proportional to the square of the diameter, so a 77mm filter has a 32% greater area than a 67mm filter). </NITPICK>
