I know that the effective aperture reduces with the amount of the extension. This smaller effective aperture increases DOF and reduces the light, so why wouldn't it also increase the visibility of dust like real aperture decrease would as it is effectively the same thing.
DISCLAIMER: Of course I could be completely wrong as I am playing with this photography stuff for only a year and few months. > Darned if I understand what relevance that has to anything in this > question thread, David. > > When you're focusing, you're moving the lens body further away from the > sensor/film plane. The nodal point is essentially an illuminating body > from this point of view, and light falls off at a rate equal to the > square of the distance (Inverse Square Law). The closer you focus, the > further away from the sensor/film plane that illuminating body is. At > some point with a macro lens, the light falloff due to extension > becomes significant and you have to account for it in your exposure. > Nothing about the aperture changes, unless the macro lens has some sort > of auto-compensating diaphragm mechanism: the light is simply becoming > less bright through distance. > > What this has to do with the imaging of dust at small and wide lens > openings is a mystery.
