Originally posted by TerryL
Where does the minimum working distance come into play?
When I am shooting macros, often I'm trying to get maximum magnification - as close to the subject (usually an insect) as the lens allows. With a 90mm or 100mm macro lens, this is usually around 30cm away from the camera sensor. For the legendary
Pentax A* 200/4 Macro, the minimum working distance is nearly twice as far - 55cm! Having the minimum working distance being further away is useful because you are less likely to bother the insect, and also less likely to cast a shadow while shooting with the sun at your back.
Edit: as @stevebrot points out, I really should not be conflating "minimum working distance" with "minimum focus distance",

but I'm afraid to change the terminology mid-discussion. The same principles apply to both, though. What it boils down to is with both the Pentax 100mm Macro and Irix 150mm Macro, you have to set yourself at a similar distance from your macro subject in order to get true 1:1 magnification. So, for
my use, there is no improvement going from a 90 or 100mm macro to the Irix 150mm.