Although I am sure the Sigma 50mm f/2.8 Macro is a good lens my preferences would be for something with a little longer focal length.
I was lucky enough to buy a new Minolta 100mm Macro D some time back now having already used a 50mm Macro on Minolta X700 (sometimes with extension tubes) and being appreciative of the extra lens to subject distance that the 100mm focal length provides.
One problem with short focal length Macro lenses is that by the time the subject is in focus at 1:1 then just the camera body and lens can be blocking out much light, let alone the photographer.
With the short depth of field at wider apertures one may be better shooting at a smaller aperture anyway. I find f/32 a pinch at times. This leads on to consideration of Macro Flash. Before buying it may be worth finding out what the Macro flash options are.
For example the Minolta Macro Flash 1200 Ring and 2400 Twin Flash come with adaptor rings to suite lenses 49mm and 55mm filter threads, the Ring and Twin Flash each having their own pair of rings.
I also find the Minolta AngleFinder Vn very useful when tripod mounted. I have a VG Manfrotto tripod with an excellent all axes head and often mount the camera on a Velbon Magslider which allows small lateral movements and linear adjustments for fine focus as manual focus is best used for many subjects. One associated problem here is in warm weather the neoprene grip pad of the Manfrotto head softens and allows the camera to droop off target when attempting portrait format shots. I have got a right-angle Manfrotto head mounting which can be useful.
Although by the time one has all this lot assembled; camera, macro lens, ring or twin flash, right angle finder, right-angle head mount, Magslider and the tripod carefully positioned and adjusted it is getting dark and time to pack up.
Portrait format seems benighted with both on camera bounce flash and such macro work.
Under these circumstances I find the automatic lens focus movement at switch on a blasted nuisance because having set up the camera waiting for a subject to land in picture I sometimes have to take a break so switch off the camera in the interim. On return, the lens hunts at switch on and I have to re-focus.
I have recently considered looking for a Minolta AF 200mm f/4 Macro G (or was a D available?) but this animal has a 72mm filter thread so the flash may be a problem.
'Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety.' - Benjamin Franklin
