Why do you say that? I never said, implied. or forgot that! Are you trying to say that because the optical path is not cylindrical that the rear element's full area is always in the optical path even at small apertures? If so, I would not agree with that...
JCO -----Original Message----- From: Raimo K [mailto:[EMAIL PROTECTED] Sent: Thursday, July 29, 2004 2:01 AM To: [EMAIL PROTECTED] Subject: Re: Scratch on rear element 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 >
