On 13 July 2012 22:40, Darren Addy <[email protected]> wrote: > On Fri, Jul 13, 2012 at 2:42 PM, John Francis <[email protected]> wrote: >> The laws of physics suggest you are mistaken here; if you spread the >> light energy out over a larger area it's not going to be as bright, >> no matter how that spreading is done. You'll lose a little bit of >> the light with an optical TC - nothing is 100% transparent - but to >> a first approximation the two ways of getting to 1:1 are equivalent. > > Thanks again to John for forcing me to exercise my Google Fu on this subject. > Found a great paper entitled "Supermacro Photography and Illuminence". > The part we need for this discussion is the table here: > http://www.antiqueauto.org/assets/LightLossWithVariousMacroMethods.png
The table is wrong (for ext tubes), John is right. See, for example: http://www.shutterbug.com/content/photographic-super-course-macro-photograqphy-page-2 "...This means that, when the 50mm lens is set at f/8 and attached to a 50mm extension tube, the effective f-stop of the combination if f/16—two stops smaller than f/8." -- 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.
