I own the Tamron 90, and it's my most used lens. Absolutely love it. I had the older generation Sigma 17-70 (f/2.8-4.5), and while it took great pictures, the macro ability wasn't what I was looking for. My buddy has the Sigma 105mm ( a lens praised for its build quality), and while it does feel a little heavier/beefier, and not as "plasticky", I don't see it as any better than the Tamron for that reason. The Tamron is plasticky feeling, but it's weight feels good, and it's not like people are throwing these things at walls. For me, I understand that it's an expensive piece of electronics, so I treat it as such, and am careful. I would also think the build quality must be pretty decent for them to slap a 6-year warranty on a new model (if you purchased it in Canada, believe it's three years for the US). If they thought they were going to have to replace it early in the game, I don't think they'd be slapping such a long warranty on it. They'd go with a crappy one-year warranty, and call it a day.
As the others have said, you'll get great image quality from nearly any macro lens, and since a lot of macro work is done shooting manually, a lens like the Pentax 100mm f/4 is really a bargain on all fronts. You get the sturdy metal build, you'd be stopping down past f/4 anyway, and you get the great Pentax color rendering. I like my Tamron because it gives ideal macro results as soon as I stop down to f/8, plus I can shoot portraits wide-open, and it doesn't have the super-sharp, unflattering for people factor, to it. The slower auto-focus doesn't matter to me because the person is stationary. The Tamron being an older lens is a non-factor, as old M series Pentax macro lenses rock on any camera. They haven't changed anything on it for a reason -- it delivers. The Sigma 105mm shows up in the Marketplace every now and then (believe there is one on there right now for about $280), and can sometimes be found on eBay, too. So a few options.
Every lens mentioned in this thread will give better results than the 17-70 -- I guarantee you that.
Just a few thoughts.
---------- Post added 09-10-14 at 01:12 PM ----------
Originally posted by pgamble Tests and reviews for the lens Pentax smc D FA MACRO 100mm F2.8 WR - DxOMark - sharpness / resolution seems to get a very poor result. I have to confess, I struggle with this because I love the DA*300 which didn't do great .. but it does suggest that the lens isn't meeting capabilities of the K5, let alone the K3. I would want the lens no to be the limiting factor in imaging.
How is there this disconnect with apparent image reviews and technical performance ?
Paul.
While I love to read reviews, I trust the samples that people post. Look at the results of some of these lenses in the various lens clubs, or do a little Googling. I don't have the experience of some of the other board members, but I trust my eyes. A lot of the stuff they talk about in reviews (corner softness in particular) isn't nearly as noticeable to me (if at all) as they make it sound. Or it would disappear when cropping, anyway. Plus they may have gotten a lesser quality sample. Sample quality is always a factor, unfortunately. That's why I like buying used lenses from PF members, as they have the body of work from the lens, and I know what I'm getting into.
Any respectable macro lens, some practice using it, and some light -- will deliver for you