Well, it is not only that. Primes simply transmit more light. Each piece of glass in a lens absorbs some light, as do each air/glass interface (although air/glass losses are reduced by modern multi-coatings) So a Prime (f/2.8) with 4 elements and 6 air/glass surfaces will transmit more light than the same f-stop zoom with 10 elements and maybe 13 air/glass surfaces. The f-stops are the same the T-stops (transmission-stops) are far different. The zoom is likely to lose a whole stop compared to the prime.
-- graywolf http://www.graywolfphoto.com http://webpages.charter.net/graywolf "Idiot Proof" <==> "Expert Proof" ----------------------------------- Igor Roshchin wrote: > > Tue Jun 27 19:37:54 EST 2006 > Joseph Tainter wrote: > >> "A prime 2.8 lens is actually faster than a 2.8 zoom because of the >> increased contrast which you'll find remarkable in comparison to your >> zoom lens." >> >> Got that? >> >> Joe > > > Joe, > > I have been working with students of different levels, so, I've seen > very curious nonsense-sounding statements. > So, let me try to guess... > > I think the author meant to say that zoom lenses more often than prime > lenses tend to be soft when wide open. So, if you have a zoom lens, > and want the best quality, you'd need to stop it down. Hence, > such a zoom is effectively slower. > > Igor > > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
