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 As you can see from that table, the Tamron extension tube (which has the same magnification ratio as the 2x teleconverter) does result in the loss of one stop of light. However, this is a stop better than the 2x teleconverter. The trade-off is that the teleconverter (in exchange for your loss of the stop of light) increases your lens to subject distance (which may be beneficial for things that wish to fly away when approached, for example). Put another way, the Extension tube costs you only as much light as the 1.4x teleconverter, but gives you the magnification ratio of a 2x teleconverter. Interestingly, close-up lenses are often looked down upon, but they lose you nothing, according to this paper. *Good achromatic* close-up lenses (as opposed to the cheap +1, +2, +4 diopters ones) can get you very good results. A couple of links on that subject: http://www.angelfire.com/ca/erker/closeups.html http://fuzzcraft.com/achromats.html http://www.robsheppardphoto.com/download/pdf/TOM-Close-Up.pdf -- 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.
