(This post is from an email conversation with a coworker. I thought the content might be useful for others.)
Q: Have you or anyone else used the Tamron 90mm f/2.8? For $459 I’m wondering if it worth the price or if I should just stick with the known quality of Canon. Have you compared the 100mm to the 100mm L for sharpness?
A: I’m generally a snob about sticking with the Nikon (or Canon) lenses. And even though the cost is sometimes double that of a 3P lens or more, there are two things that make the additional cost easier to swallow. First, bodies come and go, but your lens investment will span decades. I have a number of great Nikon lenses that I’ve had for 20+ years that work perfectly with my latest Nikon bodies (e.g., 300/4 AF, 180/2.8 AF, 85/1.8 AF). Second, OEM lenses depreciate much less than 3P lenses do. In fact, quite a few of my lenses are worth more now than I paid for them. So a little depreciation spread over a lot of years makes for a very good overall cost proposal.
WRT 3P lenses, in nearly every case the 3P lenses produce visibly inferior images compared to their OEM counterparts. And in most cases, the build quality and sealing is much poorer. Finally, the resale value is much lower.
All that being said, the macro lenses, and specifically the 90-100mm range products are the one sweet spot for the 3P manufacturers. Most of them are good, and the Tamron 90/2.8 specifically has always been an excellent lens throughout the many versions. I’ve had two of them and at one point (back when I had time (= before kids)) I tested all of my lenses and the Tamron 90 was significantly sharper than every one of my excellent Nikon lenses. (The Nikons did beat the Tamron for contrast, though.)
The Tamron build quality is decent, and it actually holds its value better than other 3P lenses. One note of caution, though, is that the chips in the Tamrons sometimes are not compatible with new bodies (at least on the Nikon side), so you may not get the same life span out of them. (That’s why I’ve had two of them instead of just one…)
And a final note on the original question, I haven’t used my 90mm Macro in probably two or three years. First off, I don’t do that much closeup stuff. And with many subjects you just have to get too close with a 90mm (even worse with a 50 or 60). So when I noticed how well my 300/2.8 AFS with a 2x converter could do with small subjects from three or four feet away, I’ve been using that combo ever since. I can take pictures of all sorts of cool bug stuff without disturbing the bugs or modifying their behavior in any way.