Concept: 3 out of 5
Execution: 2 out of 5
Yeah, but: Whose throat is it, anyway?
The Long Version: I've now been using the Sigma 150mm f/2.8 DG EX Macro for four months - out of the six that I've owned it. My initial review dealt with the unpleasantness of learning that no shipping Sigma 150mm Macro lens will autofocus on an Olympus E-3 without a trip to the Sigma service center of your choice, so I won't dwell on that any more here except to say that you should make certain that the warranty covers your location, because you are going to need it. This review is just looking at the performance of the post-update lens.
Imagine an autofocus system is trying to catch a bus. Some lenses can sprint so quickly that they're never late for work, like the Olympus 12-60mm. Some get up a brisk run, holding their pockets so that nothing flies out. This would be the 11-22 or the 50-200. Some walk with dignity, thinking that if the bus leaves then it wasn't worth catching. The Oly 50mm f/2 macro comes to mind. The Sigma 150 Macro is the lens that stumbles and breaks its ankle.
To be fair, the Sigma is a macro lens, with an extremely long focus range that needs to be adjusted with great precision. It's not designed for speed, a goal that it achieves admirably. When it only needs to make minor adjustments, everything is fine and it works just like a normal lens. It does have focus-limiter switches, so it's possible to reduce the amount of hunting when it misses. These also serve another purpose: they can force the lens to shift its focus to the desired range. When the lens is at infinity when I want to take close-ups, or vice-versa, the boke(h) is so smooth that there's no contrast for the AF system to pick up, and the lens won't move at all. So cycling the power on the camera or flipping the focusing range is about the only way out. Sigma doesn't advise using the AF+MF mode on a 4/3 body, or adjusting the manual focus on the lens unless the body and lens are both in MF mode.
But the problem is that it's not all bad. When this lens is snicking into focus properly it really does some beautiful work. Optically there's absolutely nothing wrong with it, and there's a reason why a 300mm-e lens is a popular focal length. It's fantastic for portraits and stand-off photography of all kinds, and as a macro lens it gives plenty of working distance. If you're working with insects, models who will be patient, or anyone else who won't be discouraged by your frequent bouts of self-referential swearing, this is a fantastic lens. But it's worth noting here that I've tried the Sigma 150 Macro in other mounts - on a Canon 5D, 50D, Nikon D80, and D700 - and while the focus travel speed is the same, the lens gets into focus in fewer steps. With the EF and F mounts, it's 'almost - done', with Olympus it's 'almost, nearly, a little more, okay, that's it.' I'd hate to anthropomorphize, but the Sigma-Olympus combination just seems to need more guesses to get to the right answer.
Of course macro photography is often done with manual focus, in which the Sigma excels. It's capable of a 'life size' reproduction, which translates to really, really big. Working distance at full magnification is about 8" from the front element, or 5.5-ish from the front of the hood. That's enough room to comfortably fit the Olympus 50/2 macro - with its hood extended -between the Sigma's hood and the subject. Not too shabby. Using the E-3's flippy screen and magnified live view makes manual focus a wonderful way to work. Add the Sigma's solid tripod mount and this becomes an exceptional combination for photographing really small things.
Sigma's tripod mount is awesome. It was one of the highlights of my first look at this lens, and it deserves a special mention again here. The collar is split with a hinge, and tripod lock knob is sprung and clips over a peg on the other half of the mount. The lock knob has a cam design that locks securely with half a rotation, which is much more elegant than the thumbscrews that other manufacturers use. The collar can be opened and removed quickly and without needing to disassemble the camera. There's a best-of-both-worlds aspect to this, because the Sigma 150 is quite small for its (effective) focal length and is comfortable to hold without the tripod mount, but it's long enough that using proper support makes composition much easier. When I'm hand-holding the camera I'll lock the collar around the strap on one of my Domkes, which is a quick and easy way to stow my monopod. The collar is even faster than a quick-release plate, so there's no reason not to use the lens in the best way for each particular moment. The Sigma 150 Macro goes from party to business faster than a speeding mullet.
I bought the Sigma because I wanted the Olympus 150mm f/2.0. I love the working distance for macros, and have a tendency for tight telephoto shots in my personal work, so it's a good fit for me. The problem is that I still want to buy the 150/2.0 - the Sigma has proven for me how suitable this focal length is without really giving me what I want from a lens. But I like the Sigma as well, and I still need its macro performance. So if I win the lottery, maybe I'll be able to have a head-to-head comparison, and can actually see myself keeping both of them.
One thing that I've found with the Sigma that cuts down on its utility is that every photo that I've taken at infinity with the 1.4 teleconverter has been soft - this isn't something that I've tested rigorously, as the results were bad enough from my one afternoon out that I haven't tried it again. (Despite ample evidence to the contrary, I don't actually make an effort to take bad photographs.) Shorter focal distances seem unaffected, but don't buy this lens thinking that it can be painlessly turned into a 210/4.0. I've also had occasions where the lens/camera combination won't respond to anything, and I need to switch the camera off and on again. And one afternoon my E-3 lost connection and displayed F-- twice. There's no pattern that I've been able to find, but these are just little things that I've never noticed with my menagerie of Olympus glass.
I've had a hard time coming to terms with the Sigarette. Using it reminds me of a computer industry expression about the value of having "one throat to choke". This is supposed to illustrate the value of having only one place to put the blame when something goes wrong; ironically it's a perfect reason to buy Apple computers, but it's almost invariably used by PC-Windows integrators. I suppose they have more things go wrong, but I digress.
What we have here is a failure to communicate, or at least a failure to optimize. And because there's two companies involved, it's impossible to say who's at fault. (Sigma.) The 150 Macro focuses more quickly on bodies from Canon and Nikon, so is Olympus autofocus inherently bad, or has Sigma failed to give the same care and attention to the four thirds mount? Really, it can be argued either way. (Sigma.) But the end result is that this lens is as good as it will ever get; Olympus isn't likely to rework their AF for Sigma, even though they are both nominally members of the 4/3 format, and Sigma isn't likely to start caring about the performance nuances of a lens that doesn't even work right out of the box.
Ultimately this is a very different animal from the Olympus 50mm macro, and there's a place for it in the four thirds lens lineup. When the camera and lens get along well, it produces some wonderful photos at all distances. It's sharp, distortion free, has great colour, and gives beautiful boke(h) in front and behind the plane of focus. But it's not a poor man's 150mm f/2.0, no matter what SLR Gear says. They've probably never actually tried the Sigma 150 on a 4/3 body, and are just going from the results that they've seen on other brands. It just doesn't work that way. In fact, I'll place a wager that even after reading all this, when you try the lens in person you'll still be surprised at just how balky the autofocus can be.
But don't say I didn't warn you, and enjoy.