Eh.. there is no Minolta 28-105 f2.8 but there is Tamron SP 28-105 f2.8
Although, it is not as sharp at f2.8, it is very sharp at f3.5 onward. In the field, I hardly shoot anything less than f5.6, I use f2.8 sometime, but find it is a little soft, but very much acceptable for people photography. You can always put some sharpening in Post processing stage. Anything else, you also don't shoot with f2.8 because of depth of field.
Tamron SP 28-105 f2.8 has to be one of the most versatile lens... hehe.. I always said this lens is for lazy people... because it zoom from 28mm to 105mm and keeping f2.8 constant.
I was thinking of selling it but not much people interested on this lens... I have too many lenses and I can't keep them all.. hence it will still be up for sale if someone wants it. If you want it, just PM me..
Regards,
Hart