Question: Which of these is an ultra-fast prime lens, four times as light-sensitive as pro zoom lenses?
It’s a trick question: They both are. In fact, both of these lenses have the same focal length and aperture. On the left is the tiny Nikon 50mm f/1.4 AIS. On the right is the new Sigma 50mm f/1.4. You might ask: Why the heck is it so huge? Part of it is the addition of a fast, silent focus motor, but most of it is Sigma rethinking what the role of a fast 50mm lens should be.
The optical formulas in most 50mm lenses date back decades, to when they were the absolute standard lens, sold included with most new SLR cameras. They were optimized to be light, cheap and, when you closed the aperture a bit, sharp as heck. It worked great, since without modern autofocus systems it was hard to shoot them wide-open anyway. "f/8 and be there," the saying went.
Flash-forward to today. SLR autofocus, for all its quirks, tends to work astonishingly well. Moreover, zoom lenses have taken the place of the kit 50mm lens, and with computer-aided design even most of the cheap ones are pretty darned sharp at moderate apertures. So if you’re going to shoot at f/8, why not have the convenience of a zoom? The main advantage today of prime lenses is that super-fast aperture for low-light shooting and paper-thin depth-of-filed — but most 50mm lenses, designed for a different era, aren’t all that great wide-open. Heavy vignetting, low contrast and choppy bokeh abound. (The brand-new Nikon 50mm f/1.4G isn’t available for testing in the States yet).
Sigma, normally branded as a budget lens company threw a curveball, deliberately over-engineering a lens to make a better, more expensive version of what other companies were offering.
Did they succeed? Yes. The new lens is an optical marvel, sharp and contrasty even at f/1.4 and with a smooth rendering of out-of-focus areas that, while not quite as good as the best portrait lenses such as the 85mm f/1.4, at least isn’t completely outclassed by them, like every other 50mm I’ve ever used. It focuses quickly, silently and (at least on the Nikon D3 and D700) quite accurately. You can read a detailed technical report at DPReview.
But that doesn’t mean that this is necessarily the lens for you. Look at that picture at the top again. I can stick the Nikon 50mm in any pocket I have, even pants pockets, meaning there’s no reason not to take it wherever I go. To try that with the Sigma, you’d need MC Hammer pants. It’s hefty, feeling a bit unbalanced with smaller camera bodies. It takes big 77mm filters, which is great for pros with expensive zoom lenses since you can use the same lens caps and filters, but for most users it just means more expensive accessories. And then there’s that price tag — $500, twice what some of the competing lenses sell for, and five times as much as the manual focus lens pictured.
But if that’s not a deal-killer, here are some samples of the stellar image quality. Clicking on the photos will open larger versions.:
Lit by a store window. 1/50th, f/1.4, ISO 720
The highest recommendation is this: It was good enough that I bought one for myself.