Hi Malcolm, I am also a fan of the EF 100mm f/2.8 Macro USM. You make a good point about the USM making this a perfect short tele for non-macro shooting. But there is another hidden benefit from USM at macro distances - almost-trap focus. For details see: http://eosdoc.com/manuals.asp?q=E7TrapFocus
You also identified the flaw in the formula: (focus_distance_at_life_size) = 4 x (focal_length_of_lens_at_life_size) that the internodal distance is significant. At life-size, the lens-to-film distance is the same as the lens-to-subject distance, so a simpler way to determine the actual focal length of the lens is to halve the working distance (measured from the front nodal point to the subject). Cheers Julian Loke * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
