> > From: Chris Stoddart <[EMAIL PROTECTED]> > Date: 2005/08/25 Thu PM 12:49:22 GMT > To: [email protected] > Subject: Re: Wideangle enablement :) > > > On Thu, 25 Aug 2005, Steve Jolly wrote: > > > It's very very slight. I could only deduce it by looking at the > > reflection of a light fitting, as I described. At the very least the > > filter has to affect the focussing of the lens slightly, since its > > increased optical depth wrt the air it replaces will marginally > > increase the backfocus. > > Steve, > > Or maybe it's concave to make sure it *doesn't* have any effect? If a flat > sheet of glass (re Mike Wilson's suggestion) has the effect of changing > the angle of refraction noticeably at higher angles of incidence (and > this *is* a wide angle lens) then it would make sense to offer up a > concave (diverging) lens to counter the converging effect of diffraction? > :-) > > Chris
Either way, the filter would be a _neccessity_ in the light path to form a sharp image. I have a 300/2.8 with rear filters. The manual says that a filter _must_ be in place at all times. This is all very interesting. m ----------------------------------------- Email sent from www.ntlworld.com Virus-checked using McAfee(R) Software Visit www.ntlworld.com/security for more information
