On 13 July 2012 23:50, Darren Addy <[email protected]> wrote: > Eric, > I think you misunderstand the table (or perhaps the table words it > inelegantly). > When the table says "1 focal length extension tube" you are thinking > the same focal length as the lens (50mm lens = 50mm extension tube). > However, what it *means* is the amount of extension needed to go from > 1:2 to 1:1 (effectively doubling the focal length/magnification). In > the case of the Tamron 90mm f2.5 the extension tube is 45mm long (not > 90mm long). Therefore the light loss is 1 stop (and the table is > correct).
I'm going to have to think about this again too. Time for bed now though. -- Eric -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
