I’ve had the fortune to have these two lenses to shoot with for a while now. I own the Nikon (Nikkor to be exact) and the Sigma was a nice loaner from Gentec International, the importer for Sigma in Canada. I figured I might write down a few thoughts.
Introduction
The "normal" 50mm lens is typically one of the cheapest lenses, included with many a film SLR. On full-frame, it is a normal lens, offering a perspective that is fairly close to what the human eye sees, whereas on a cropped sensor camera, it offers a medium telephoto view, quite suitable for portraiture. That being said, I rarely use one! Why? Simply because I prefer to use either the wider Nikkor 28/1.4, the longer 85/1.4, or for weddings I’ll use a zoom for flexibility. I have recently become reacquainted with the 50mm range with these two lenses and it’s been a nice change of pace.
Build Quality
The Sigma certainly makes an impression with its size and heft. It is a hefty beast — you get the feeling that the Nikon could easily slip inside it. It’s a bit hard to believe that these are both 50/1.4 lenses — in fact, the Nikon 85/1.4 is just about the same size as the Sigma. It’s obvious that Sigma threw their technological know-how at this lens. It has a huge 77mm filter diameter, a huge front element, and is packed with aspherical elements, none of which are to be found on the Nikon. The balance is pretty good, and it has a decent, solid feel. The surface finish is a slightly rubbery, textured finish that seems to be flocked on, but I’m left wondering how durable it is. I’ve always found Sigma’s cosmetic details just not up to the same quality, and this has probably nothing to do with the internal quality, but just purely the little details that are different.
Nikon’s offering matches their cameras, as would be expected, with the same textured plastic housing as its consumer-grade lenses. Its build quality is different from the Sigma — not necessarily better or worse, just different as it almost feels like a different target market. It has a rear rubber gasket to help seal off the gap between the lens and lens mount, has a useful lens indexing dot on the housing to help align the lens properly when mounting it.
Performance
Both lenses are awfully close in performance in many, many respects. I don’t test lenses methodically with resolution charts, rather with real-world subjects, so I can only give you a qualitative feel for them, but my findings appear to echo the general sentiment on the Internet. So here goes: Both are sharp wide-open in the centre, but the Sigma may have a tiniest of an edge. The Nikon appears to better the Sigma in the corners. Wide open, both lenses do have a slight veiled softness to them, as would be expected. By about f/2 or f/2.2, both lenses have cleared up, with Nikon probably still a bit ahead in the corners. Above about f/5.6, they’re really tough to tell apart. They’re as sharp as can be, even on the D3x I was testing with.
One thing that struck me right away was that the Sigma isn’t a 50mm lens. Or the Nikon isn’t. The Sigma is maybe around a 45mm lens in relation to the Nikon. The difference is definitely noticeable when comparing both lenses side by side from the same shooting spot. This may be focus breathing (i.e. the focal length changing a little depending on focus distance), but my shots were taken over a distance so that shouldn’t be a factor. My particular sample might suffer from a tiny bit of a centering issue, with sharpness not quite the same from edge to edge, but you would have to be pixel peeping the D3x image to see this.
Fall-off (vignetting) is noticeable on both, but the Sigma is definitely better than the Nikon. The Nikon takes until about f/2.8 to be mostly visibly clear of the darker corners while the Sigma is similar by f/2. The Sigma’s ability to evenly light the frame is impressive, no doubt due to the oversized front element.
Bokeh appears better on the Sigma as well, wide open anyway. The Nikon isn’t too bad, and it’s certainly better than the AF 50/1.8, which I think is one of the uglier lenses in this department, at least in my lens collection. However, the Sigma is definitely smoother and somehow able to generate larger blur circles than the Nikon.
The Sigma is a faster focuser than the Nikon, but louder. The Nikon is extremely silent. I may have noticed perhaps a little bit more AF hunting on the Sigma, but it might just have been me.
Bottom Line
Not too surprisingly, the lenses are quite similar. Sigma has taken a bit of a brute force approach with the lens, probably with a mission to make it the best 50mm SLR lens for full- and crop-frame cameras. The lens gives sharp, smooth images, focuses very quickly, and feels good in hand. It feels more biased towards someone that has some very specific needs for shooting wide-open or close to wide-open and retaining very good bokeh and optical performance as well, especially corner fall-off. You can definitely shoot some nice portraiture on this lens. The downside is that it is a fairly chunky lens, something that one might think twice about putting in the bag.
Nikon, on the other hand, has opted to keep the spirit of the 50mm lens and kept it pretty compact and light, yet endowing it with excellent performance. It gives a different combination of characteristics, favouring corner performance and small size and while giving up a little on bokeh, fall-off, and autofocus speed. It’s perhaps a bit more of an all-rounder, jack-of-all-trades lens. And it’s cheaper than the Sigma by over $100 CDN.
Which one to choose? I think it’s pretty clear you’ll get stellar images from either and they’ll be pretty tough to tell apart if you stop down a few to f/5.6 or better. If you’re shooting wide open to gain a specific look, like great bokeh, or really crave the best low-light performance, the Sigma does everything a pro or discerning consumer would want from a 50. If that isn’t quite your cake and you simply want something to put in your bag for the rare occasions when you encounter low light, or you want amazing quality across the frame, then the lighter, cheaper Nikkor would be the way to go.