You should know that that lens has a defect where the AF motor grease causes some issues. I think it slows the AF motor and leaks onto the AP blades. It's risky buying one from Ebay. FWIW the 100mm didn't have this problem and is a little better lens. You definitely won't have to get as close which IMO can be good and bad...
Steve, Mike is right about the lenght of the Macro lens. The longer the better generally - better being longer working distance in front of the lense i.e. focuses on something further from the front of the lens. Some things are too skarit to get as close as a 50 mm. If you can find a Minolta mount macro in 150 - 200mm the better. Pricier usually though. Also, I wouldn't be too concerned about AF in a macro lens. Most don't do too well at AF on something that close. Plus at that depth of field, you might want to change the focus from what it is focusing on to another part of the flower or insect i.e. you would usually want an insect's eye to be in focus, but the camera may be focusing on something else if set to automatic. If I was to get a macro, I would definitely look at some of the older non-AF glass. Some great glass out there, and why pay for some features, you might not use anyway. Macro work is usually not snapshot work, it is quite often tripod work because of closing down to try to get as much depth of field as you can and the ensuing long exposure times. "Macro capable" and dedicated Macro (or Mikro if Nikon) lenses are usually good to a 1 to 1 ratio - in other words, life size. The image is the same on the "film" as in real life. For lots of bigger things that is pretty good, but if you want bigger magnifications on tiny things, you have to do other things. There are other ways of getting macro, especially in the greater ranges than a lens - screw on diopters, bellows, extension tubes, stacked lenses, reverse coupling - that can be less expensive than buying a dedicated macro lens but usually with some tradeoff. Screw ons won't get you much macro and can degrade image quality. Bellows can be big and unwieldly and there is a loss of exposure and usually some of the lense's automatic functions won't work- but almost unlimited range of macro reproductions. Extension tubes are essentially fixed bellows so are limited to their lengths or their combined lengths if stacked - also loss of exposure and usually some fo the lense's automatic functions don't work. Stacked lenses can be fun and can get some much higher magnifications shall we say. Vignetting can be a problem, all lense can't stack and you need an adapter to fit the front filter screw threads on each lens - the prime lens will still have all it's functions and it would be best if you could set the front lens wide open. Reversing a lens is also fun, - bigger magnifications, but with a loss of lens automatic functions and you need an adapter, plus the rear of the lens with all the coupling mechanisms is sticking out front and you might need to be careful. On the midge photos, I reversed either a 28-80 or a 18-135. No loss of light, and the zoom works to give variablilty to the magnification and working distance. The AF did not work, but the camera figured the exposure with no problem.
