Macro Performance on A900 vs A700

[Greg Beetham]

I thought that once you go beyond 1:1 on a macro lens, (such as using it on the end of tubes or a bellows) it stops projecting the standard field size for it's format, and projects a much larger field, the size of which depends on how far out in front of the camera the lens is, and all the sensor (whether it's an APS-C or FF or 4/3) is doing is sampling a small portion of that projected image field, the major penalty being light loss, even at 1:1 with a standard macro lens there is an exposure correction of 2, and it gets worse from there, the more you rack the lens forward from the sensor/film plane.

When you go up in magnification (larger than lifesize) the smaller format "should" be at an advantage over the larger format, it is in effect sampling a smaller section of the projection per extension setting (given the sensor/film to subject distance remains the same), the only reason I would use the larger format is if I thought there was a chance of putting more photosites under a given subject size with it than with the smaller format, (wide angle macro) so that would really depend on the size of the subject and how close you could get to it.
Greg