What is your budget? Here are some > 50mm:
$50-90 - Vivitar 135mm f2.8 Close Focusing (1:2)
$100 - Pentax/Vivitar/Cosina/Phoenix 100mm f3.5 macro with matching 1:1 lens (used, maybe old stock)
$150 - Tamron 90mm f2.5 Adaptall-2 52B or 52BB (later version, optically same), 1:2
$200 - Tamron 90mm f2.8 Adaptall-2 72B 1:1
$250-$300 - Vivitar Series 1 or Kiron 105mm f2.8 1:1, Tamron 90mm f2.8 Di non-Adaptall
$400 - Pentax DFA 100mm f2.8 1:1
$750 - Sigma 180mm f4 1:1 (not sure on this one)
~$2000 - Pentax A* 200mm f4 1:1 but very rare
Other options:
Extension tubes.
Pentax 50mm macro.
Flektogon 35mm f2.8 (about 1:2 maybe closer?).
Vivitar 2x macro teleconverter.
And ricosauve's link above has even more I forgot about.
My recommendations:
The Pentax/Vivitar/Cosina/Phoenix 100mm f3.5 is nice lens if you can live with a light plastic build. The lightness can be an advantage depending on how you shoot. Without the matching 1:1 screw on lens (on to the front) it is 1:2. I've got some good shots with my Vivitar-branded version and I am keeping mine even though I have better macro lenses now.
Tamron 90mm f2.5 Adaptall-2 52B/52BB is an *awesome* lens in both build quality and optical quality. It is 1:2 and requires an Adaptall-2 PK (can be found cheap) or PKA (harder to find cheap) adapter. There is also a Tamron flat-field adapter that goes on the rear between the lens and the mount adapter to get to 1:1. I don't have that adapter but I do have the 52B model of this lens and I love it. It's great.
Tamron 90mm f2.8 Adaptall-2 72B is a nice lens. It can go 1:1 without an adapter. The only downside is the focusing mechanism is internal so at 1:1 the lens is closer to the object than some other 90mm/100mm lenses. The long built-in hood doesn't help much either. This lens typically earns it's keep as a portrait lens though and at that it is great. It's not too shabby at macros at all if the closeness isn't an issue to you. I like it but I don't know if I'll keep it. I'm curious if the later 90mm Di non-Adaptall version is the same with the closeness.
Vivitar Series 1 105mm f2.5 is a very nicely built lens that rivals the Tamron 90mm lenses for sharpness. I have noticed in mine that it may have a tiny bit more purple fringing but I haven't tested for this. It's nice but it is also very heavy. The Tamron 52B is heavy too but it is more stubby and easier to hold. Of course the 52B only goes 1:2 while the Vivitar goes 1:1.
Last edited by cmv; 12-10-2007 at 01:10 AM.