9 out of 10 points and recommendedsize, weight, build, rear focusspinning focus ring during AF
I suspect any negatives about this lens wide open come from AF inaccuracy. On bodies that have AF fine tune abilities, with some tweaking, this lens is DAMN sharp wide open. A bit of field curvature up close, but not and objectionable amount. Again, it's down to AF--if you choose a proper point and the camera nails it, you're golden.reviewed November 2nd, 2010 (purchased for $230)
I wouldn't count the lack of AFS as much of a negative, except in circumstances where you hand you camera to some one else--as a pro, this is pretty never.
The AF issue may or may not be because of the screw drive, but I have noticed that newer bodies are consistently bad at focusing these screw drive lenses at default settings. For example, the D90 is inconsistent and the D200 wasn't very good with it either. D300, D700, D2x, and D3 were all great, but only after adjustment. And the amount of adjustment was different for each body (among similar AND different models).
High contrast situations can excite some LoCA--but that is so for MANY lenses, even the 1.4D and the new 1.4G. It's just a fact of life, and one that's hard to cure in post. Pretty much goes away stopped down.
Great bokeh, with a caveat: edge quality of point light sources can be excellent to mediocre, depending on subject distance. I'm not talking about just the amount of blur, but the quality. It does actually tend towards 100% neutral at closer focus distances. Very subtle ringing as you get closer to infinity, but never objectionably so.
In closing: an undervalued gem!
9 out of 10 points and recommendedsharpexpensive
Reviews for this lens are all over the place. I demo-ed one of these and it didn't knock my socks off compared to my 1.8. It is absolutely sharper...but not $1500 sharper. And it's a substantial lens in terms of size. Weather sealing and AFS are welcome additions. But not for the money involved.reviewed November 2nd, 2010
A word of caution about some of the reviews going around: adapting rear focus lenses for use on other bodies will get varying results that don't always reflect the quality of the optic involved. Rear focus designs like this are designed in such a way that the static front groups have to be fairly precisely positioned in relation to the plane of the sensor/film. Third party adapters are a) suboptimal and b) not consistently sized. One can luck out and get a good one, but it's a crap shoot.
As far as comparisons to the 1.2 canon: all three Nikkors (1.8D,1.4D,1.4G) have much nicer bokeh at full body portrait lengths. It's not as extremely different as 50mm lenses, but it's noticeable. All of these lenses get a bit ringed at further subject distances. This newest 1.4G is no exception. It is, however, best in class.
10 out of 10 points and recommendednothing else like it, wide, fast, close focusbig, janky focus selection
Ain't nothin else like it. Literally it's own class. Nothing that's simultaneously as wide and as fast.reviewed November 2nd, 2010 (purchased for $400)
A touch soft wide open, but this is mostly noticable in daylight. It's a bit dreamy wide open in bright light. However, in dim light, when you need it, the fine detail is certainly there. Even out to the corners. Remember, even at 20mm, 1.8 is VERY shallow. My Nikons have always done well with this lens, but YMMV when it comes to focus accuracy. I believe I have some correction dialed in on my bodies. Canons seem to struggle with this lens.
There are some complaints below about having trouble focusing in low light--this is true of MOST cameras and lenses this wide or wider! Try it with lenses in the 14-16mm range and you'll see the same. It's a technical limitation, not a lens quality issue.
Also, a story about build quality and warranty repairs: the lens feels rather robustly built, but as I was transitioning from film I was using this on a D2x. The D2x and this lens destroyed each other. The aperture bladed crumpled and the aperture arm on the camera stripped. Nikon fixed the body under warranty (only a couple months old!).
The lens however was just shy of four years old, and just about to go out of warranty. It took Sigma at least EIGHT attempts to properly repair my lens so that a) the aperture blades didn't implode and b) it was as sharp as it had previously been. In seeing how this lens performed when improperly re-assembled, I can imagine that some must come from the factory that way and be very soft.
I'll give Sigma credit: they kept trying until it was fixed to my satisfaction. But you can see from this story that there is the potential quite a bit of variation in quality in the end product.
Something I don't see often in reviews of this lens is it's close focusing capabilities. It can focus VERY close--within an inch of the front element! Combined with it's wide angle of view this can make for some interesting effects. Also the bokeh is pretty neutral all around. Wide + close + point lights = interesting effect, for both still and video.
So, provided that you get a well assembled sample, this is a STUNNING lens, which has no other market equivalent because of many things it offers: speed, angle of view, close focus abilities.
Totally usable wide open and VERY sharp closed down.