My understanding was that this was the "effective" ratio. Like the new lenses that claim that their super low dispersion glass allows smaller sizes at the same effective speeds. How would one achieve critical exposure accuracy if f/4 on one lens was equivalent to f/4.5, or f/3.5 on another? Yikes. Or are the variations very, very small?
Don > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of > William Robb > Sent: Wednesday, June 28, 2006 6:32 PM > To: Pentax-Discuss Mail List > Subject: Re: Seen on eBay > > > > ----- Original Message ----- > From: "Don Sanderson" > Subject: RE: Seen on eBay > > > > Uh guys, maybe I'm missing something but unless someome is lying > > about their product isn't f/4.0 always supposed to be f/4.0?? > > It'd pretty much leave slide shooters who use a manual meter SOL > > if it wasn't, wouldn't it? > > The f-stop is a mathmatical calculation of actual aperture size vs. focal > length. > It says nothing about the transmissive abilities of the glass. > > William Robb > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
