Originally posted by yeatzee
-TBH I'm skeptical of having a full plastic lens (the tamron)......but It does come with a 6 year waranty.
-The Pentax is good from what I've read, but there is better according to all of its reviews I've personally seen.
I believe that the Pentax is also almost all plastic. Hard to say what the Sigma is made out of. All I can say is that if the construction is similar to my Sigma 50/2.8 Macro, it is probably some sort of polycarbonate with some metal components. It almost certainly is not all metal.
Edit:
Peter Zack reviewed the Sigma 105 and stated that the build is all-metal. Peter usually knows what he is talking about, so I may be mistaken regarding the materials of the EX lenses. (If mine is metal, it lacks the familiar cold, hard feel...
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End edit
For what it is worth...if money was not any object, I would buy the Zeiss Makro-Planar T* 100/2 (cuz its there...). Since money is a consideration, I would buy any of the Tamron 90/2.8, Sigma 70/2.8, or Sigma 105/2.8 with the edge being to either the Tamron (best price/performance) or the Sigma 70 (best performance).
As noted in a few of the above posts, you really should consider a used lens. This is particularly true if you are new to macro photography. There are additional hidden costs beyond the lens (things like tripods, focusing rails, lighting...). The suggested models (Vivitar, Lester Dine, Pentax-M, Takumar, and others) are excellent lenses. Don't be put off by the lack of auto-focus. You won't ever use the auto-focus for macro shots.
And while we are looking at the low end, price-wise; it might be useful to take a look at the Raynox DCR-150 or DCR-250 auxiliary lenses in combination with a near-macro zoom. Some pretty striking images on this site have been taken with this low-priced tool. Want to go lower price-wise? Think extension tubes or reversing rings. All are capable of great results with the main trade-off being convenience.
Question...What does stevebrot use? Well, I have the Sigma 50/2.8 macro that I use for flower close-ups and such. It works pretty well on digital, but really shines with 35mm film. It is convenient and handy, but the image quality is not as good as my "real" macro setup...
Yep, bellows with a decent prime up front (either forwards or reversed). Cumbersome, but elegant...it does the job in a precision fashion. To 1:1 and beyond!!!
Steve
(thinking one of these days the dedicated Pentax 100/4 Bellows lens might be nice...)