If you have a reference lens ( like the ones marked by leica ) , you can compare the relative magnification of a very distant object of the test lens vs the reference lens and use that ratio as the coefficent of the ratio of two focal lengths to calculate. jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Shel Belinkoff Sent: Thursday, November 16, 2006 11:29 AM To: Pentax-Discuss Mail List Subject: Re: K 18 f/3.5 on Digital (was Any screens formanualfocusingon*istDS?) How is one able to tell what the exact focal length of a given lens is? Or, more precisely, how do we, without appropriate testing equipment, make that determination? As an aside, Leica marks the exact focal length of some of their lenses on the lens barrel. Even though the lenses are "the same," there are still focal length variations. So, even if we can accurately determine the focal length of a given lens, it may be that the focal length of another sample is different. Shel > [Original Message] > From: Kostas Kavoussanakis > I think the K18 is also more of a 19; I seem to > have read this on the list at some point. -- 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
