Originally posted by caferacer73 Vivitar Macro Focusing Zoom 75-205mm f3.8
I have this lens and rather like it even though it has a degree of fungus in it. Actually, quite a few of the old legacy Vivitar lenses I have (and Sigma) seem to have problems with fungus or haze. Legacy lenses are obviously generally quite cheap but do need to be checked that the optics are clear, shining a torch through the lens should highlight anything on the optics.
Some old Vivitars have shrouds around the aperture lever (on K mount models) that need to be cut back to use on digital if you intend to do so. Obviously your Spotmatic is M42 so no problem.
My favourite legacy zooms are the Tamron SP range, the 60-300mm 23A is a zoom that probably beats most if not all of my legacy zooms in versatility and performance.
Legacy primes can be had quite cheap, the Chinon 200mm F3.5 0r F3.3 for example and the CZJ Sonnar 135mm F3.5 is a lovely lens but generally more expensive.
Check out the reviews of lenses here in the forums, they will be a great help.