Originally Posted by newarts 
The left photo was with a 50mm macro lens, right with a 90mm macro lens, both f4, same geometry.
That's an amazingly effective demonstration - thanks!
BTW, regarding the usefulness of the focal lengths for non-macro purposes - I actually find 100mm far more useful than 50mm. But that's because I also have a 28 and a 40 for use as "normal" lenses - I got these because I have a 50 but find it too long for most purposes. Whereas 50mm is also too short for portraits for me (not that I do portraits often). 100mm is on the long side for portraits (but still usable), but I find it *perfect* for concert photography, and long enough for general telephoto use (not wildlife) to replace a 135 in one's bag.