I had a Canon 100mm f2.8 Macro and it was working quite well for me but I longed for a little more working distance. When Sigma came out with the 150mm f2.8 Macro, I tried researching it but couldn't find much info because it was such a new lens, I found the MTF charts on the Sigma Website and it was amazing. This lens was very close to the performance of the Sigma 180mm macro and Canon's famed 180mm f3.5 L. So I went ahead and bought it. It was a little pricy but I thought I could always return it if I didn't like it.
My first impressions taking the lens out of the box was very positive. It was quite compact for the focal length and was very well made. It balanced quite well on my 20D. I never liked Sigma's EX finish but I could live with it. The EX finish looks cheap to me,particularly the golden ring, and the EX badge, but it's better than Sigma's old design. The only thing I like about the EX finish is that it seems very durable. Even after heavy use there are no marks or scratches on the lens body and every time I wipe the lens body with a damp tissue, it just looks like brand new. The focus ring is nicely ribbed and wide but it didn't have the kind of damping Canon L lenses have, so it felt a little loose. The tripod ring is made of the same material as the lens body itself, but it didn't feel as smooth as the Canon's L like the 70-200 2.8IS and the 300mm f4 IS. One advantage Sigma's tripod rings have over Canon is you don't have to take it off the tripod to remove the lens. You just pull a knob and the ring opens allowing you to remove the lens. This is good if you have it all set on the tripod and want to quickly remove it for some hand held shots.
150mm is a pretty unique focal length for a macro lens, coming up close to the very heavy and very expensive 180mm L from canon.
having a longer focal length is a double edge sword, as it can give you shallower depth of field, but also can make it harder to get all your subject in focus. The 100mm are easier to use, the 150 gives better images. The main advantage to a longer focal length is the increased distance you can put between you and your subject, which can be very useful for skittish insects, and makes it easy to get good lighting on your subject if you're not using a dedicated macro ringlight.
The IQ from this lens is ludicrous, insanely sharp from edge to edge at f2.8 and because it is truly apochromatic there is no 'colour fringing' what so ever, impressive.
AF is quick and the relatively long focal length makes it more versatile as a tele lens than the 100mm lenses. A 150mm 2.8 is a good portrait lens if you have the room.
Unlike the 100mm L this lens isn't weather sealed, although the build quality is very high- although as with all sigma products of this era they used a rubberised coating on the lens barrel which has a habbit of scratching very easily and can look tatty quite quickly, so take care and handle with kid gloves if you want it to look mint- the new sigms 150mm OS doesn't have this problem as it's made out of bare plastic.
A great lens, optically perfect, just have to decide which is better for you, canon or sigma
This is a proper macro lens, being able to focus to a 1:1 ratio, that means at closest focus an object measuring 5mm will project a 5mm image onto the sensor or film. A lot of lenses put marco on the label without having a true macro ability.
The focal length of 150mm is very versatile. You can photograph insects and other creatures without having to get too close. The large aperture of f/2.8 lets in plenty of light, and combined with the 150mm focal length allows for a beautifully restricted depth of focus. This allows details to be picked out in sharp focus, whilst throwing the foreground and background out of focus.
The lens hood is deep and fixes on tightly with a bayonet fixing. When reversed it completely obscures the focus ring, which is good as it makes you more likely to use the hood! It also comes with a tripod mount, which is ideal when used with a light camera body, but isn't all that necessary with a large pro body, this can be rotated, and also removed by loosening and the pulling the spring loaded knob out. The matt black finish is hard wearing and feels great in the hand. The focus ring is wide and handles smoothly. There is a three position focus limiter switch, full, 0.52m-infinity, 0.38-0.52m which helps in speeding up focusing. The HSM however is fast, quiet and reliable, and by being HSM allows manual override without having to change to manual. The 72mm filter size is reasonably large, but not so big as to break the bank unduly when buying filters. There is also a soft case, which is actually pretty solid.
I love this lens, it's great for photographing flowers, as you can really pick out the details if you get in close, but if you hang back with whole flowers you can get them sharp with beautifully soft foreground and background. It's also great for insects as you don't need to get too close. You can also use a 1.4 of 2 times teleconverters. So you can end up with a 210mm f/4 AF tele-macro lens or a 300mm f/5.6 MF tele-macro lens. This is a little odd, in that AF with the 1.4x converter only works down to 0.52m, and even with f/5.6 it will only MF, although this is with sigma teleconverters. With an adapted nikon, or one of the other converters AF should work with both.