You seem to forget that the transmitted light forms a cone, not a cylinder. All the best! Raimo K Personal photography homepage at: http://www.uusikaupunki.fi/~raikorho
----- Original Message ----- From: "J. C. O'Connell" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, July 29, 2004 5:12 AM Subject: RE: Scratch on rear element > What kind of vague reply is that? Not sure what that is supposed to > mean. > You were "sucked in" by me?, no you were sucked in my yourself. > If you want to "experiment", try looking at the physical construction > of a lens. You will see that as a diaphram closes down and the angle of > view > remains the same as it does for a fixed format like 35mm, APS DSLR, or > P67, > that the outer glass on the rear elements gets obscured by the diaphram. > If no light is passing thru those areas, "crud", scratches, cracks, > seperation, > coating problems, etc in those areas DOES NOT AFFECT IMAGE WHATSOEVER. > Hence, by stopping down you can elimanate those problems, they do not > become > more visible, they become less visable, Invisiable actually. Exactly the > opposite of what you rudely contended which is what promted my reply. > JCO > > -----Original Message----- > From: Rob Studdert [mailto:[EMAIL PROTECTED] > Sent: Wednesday, July 28, 2004 9:11 PM > To: [EMAIL PROTECTED] > Subject: RE: Scratch on rear element > > > On 28 Jul 2004 at 19:35, J. C. O'Connell wrote: > > > You don't seem to have a clue as to how lenses work especially with > > regard to the diaphram. As you stop down the diameter of the optical > > path is reduced proportinally. If there are scratches , etc on the > > ***perimeter*** of the rear element and the lens is stopped down enuff > > taking > > the angle of view into account, the "crud" on the > > perimeter is often COMPLETELY OUT OF THE OPTICAL PATH, I.E. IT IS > > IRELLAVANT AND HAS ZERO AFFECT ON THE IMAGE FORMED > > BY THE LENS! > > Slapping myself for even getting sucked into responding to JCO :-( > > David, when you come over next we will determine experimentally if it > does or > doesn't have an effect. Unfortunately I doubt that Kennedys will want > anything > at all to do with it particularly WRT replacing rear elements. I'll have > a go > repairing it and if I break it I'll replace it. > > Cheers, > > > Rob Studdert > HURSTVILLE AUSTRALIA > Tel +61-2-9554-4110 > UTC(GMT) +10 Hours > [EMAIL PROTECTED] > http://members.ozemail.com.au/~distudio/publications/ > Pentax user since 1986, PDMLer since 1998 >
