What I am trying to tell you is that you really can't trust them. I would measure these myself to be sure. Its easy at 1:1, just measure the distance from subject to film/sensor plane and divide by four to get the infinity focal length or divide by two to get the effective focal length which is what you would want for the IS/SR input data to the camera...You dont need to know the lens nodal point for 1:1 focal length measurement.. jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Digital Image Studio Sent: Sunday, December 10, 2006 11:12 PM To: Pentax-Discuss Mail List Subject: Re: SR effectiveness at 1:1 macro? On 11/12/06, J. C. O'Connell <[EMAIL PROTECTED]> wrote: > First mistake, never trust the lens makers claims > when it comes to focal lengths. For example, how > many of the Lens makers have revealed or specified > the actual focal lengths of these pseudo-zoom > macros? Any? Secondly, lens makers often "cheat" > when it comes to apertures and focal lengths. For > example, their 20mm lenses may all measure 22mm > but they dont tell you that in the data sheet do they? It really doesn't matter, the distance to the FL and the mag ratio are all I'm interested in, I couldn't give a FF about the FL only that I want to be able to enter it into the camera. -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
