I blogged a while ago about the pleasure of using my ancient Olympus OM Zuiko 50mm f/1.8 lens on my Sony full-frame mirrorless camera. I’ve had a couple more outings with it since the walk I described, and enjoyed it every bit as much.

I’ve always had a 50mm lens since my first SLR camera decades ago. When I bought the Sony, I was hoping to use my Nikon 50mm f/1.4 AF-S G lens with the LA-FE1 adaptor.

The Nikon 50mm f/1.4–LA-FE1 combination certainly worked, but the autofocus speed was so slow, I gave up using it. It has been my slowest focusing lens for as long as I've had it (since about 2008-ish). But on the LA-FE1 it was unworkably slow. If my primary interest was still life (or food, or post-mortems), I could happily stick with it; stopped down a little, the images have a lovely quality. As much as anything, the impracticability of the slow AF for my purposes prompted me to disinter the Olympus lens.

The thing about the old manual focus Olympus lens is that using zone focus, you don’t always have to worry about precise focus if you know your subject is within the distance of the set zone. And manual focusing is more precise and easier than on an original SLR given focus magnification and peaking.

Nonetheless, I can’t help feeling that having a high-resolution camera with one of the AF best systems in the world is a bit wasted if you use an old lens like the Zuiko 50mm f/1.8 for a main interest like street photography. It is also limited by how the lens and camera work together. At f/1.8 on the Sony, the images have such strong vignetting that they are beyond full correction in Lightroom. I don’t feel that you get the good enough images till f/4. In effect, I use it not as an f/1.8 lens but as an f/4 lens.

I’ve recently been through my Lightroom catalogue to see how much I used the Nikon 50mm f/1.4, plus what I used it for, and at what aperture ranges. (I know everyone says this every time, but this is a huge blessing of the digital age that this is such a trivial thing to do now). My prior impression was that I’d not used it all that much except in particular circumstances: my preferred “normal” focal length has been 35mm for many years, so the 50mm tended to be relegated to the bottom of the bag. What my Lightroom trawl showed, however, was I’d actually used it much more frequently than I thought, and some favourite pictures had come from it. In addition to street photography (along the lines of what I showed in the previous blog), I’ve used it for a wide variety of purposes: the fast aperture for after dark (unsurprisingly), cityscapes, portraits, and what I’m going to call details.

I’m littering this blog post with a few examples of how I’ve used the Nikon 50mm f/1.4 lens outside of street photography.

To cut a long story short, I think a fast-ish, high-quality, modern 50mm lens is going to be an essential part of my gear. The big thing is that it has to be the kind of lens I’d be happy walking all day in a city with, so not too big or heavy. I’ve indulged myself over the summer with GAS-related “research” into this. I don’t normally go quite so far down the rabbit hole as this. More often, only one lens available for a system is close to what I want. For example, the Sony 200-600mm lens was a no-brainer that required little comparative analysis, once I’d tried it out.

The thing about the Sony FE ecosystem is the huge and bewildering array of 50mm options available. Almost every manufacturer of full-frame lenses seems to have at least one. Sony alone has multiple examples: the “thrifty-fifty” f/1.8, the top-of-the-range and correspondingly expensive f/1.2, the new f/1.4, the tiny f/2.5, the macro f/2.8, the older f/1.4 Planar and f/1.8 Sonnar lenses produced with Zeiss.

In terms of other manufacturers, Voigtlander produces the manual focus 50mm f/2 APO-Lanthar which looks to be optically superb (Diglloyd describes it as a “reference lens”). There are a lot of other cheapish manual focus lenses from Chinese manufacturers, some of which aim at the Noctilux market (f/0.95 or thereabouts). Lens Light Lab produces several interesting clones of older designs: I thought their Elcan clone (M mount, but easily adapted to FE) looked particularly intriguing, although that has now gone out of production. The list of manufacturers goes on and is seemingly endless.

So where to start with looking for a lens that would suit me? Basic parameters: good autofocus; fast-ish aperture; not hopelessly big, heavy, or expensive; excellent optical performance. As a baseline, my Nikon 50mm f/1.4 weighs around 280g, so I’d be looking for something not much more than 300g.

All the manual focus lenses are eliminated immediately, including to my regret the APO-Lanthar. It also eliminates the Sony f/1.2, new f/1.4 and f/1.4 Planar lenses: too expensive and too big/heavy for a day walking in a city. f/1.4 lenses from other manufacturers (e.g. Samyang) are also out for the same reason. I’m also eliminating the Sony thrifty–fifty because the optical performance is not up to current standards.

In terms of aperture, I have to draw an arbitrary line somewhere. Looking in my Lightroom catalogue, about 1/3 of the images were shot between f/1.4 and f/1.8. Given that the difference between f/1.8 and f/2 is insignificant, and no f/1.4 lens is likely to meet my criteria of size/weight/price, I’m setting the aperture threshold at f/2. This means that lenses noticeably slower than this are eliminated: the Sony f/2.5 and f/2.8 lenses are out.

What about the Sony-Zeiss lenses? They are older designs now. The Planar is already out. The f/1.8 Sonnar ought to be an attractive option. It weighs about the same as my Nikon 50mm lens, and in the centre is reported to be extremely sharp. But the edges of the frame wide open don’t look so great, especially considering the price.

Err … well … I’ve now managed to eliminate all the lenses I mentioned to start with.

There is one lens I’ve not yet mentioned that meets most of my criteria. This is the Sigma 50mm f/2 DG DN I Contemporary lens. Too much of a mouthful: I’ll just call it the Sig50-2.

In terms of my criteria, it meets the aperture threshold, its size is OK, its weight is a little heavy (345g) but liveable, and it is beautifully built.

Optically, it looks to be extremely good. Sigma’s own MTF chart suggests that wide open it should be very sharp and contrasty in the centre, and most of the way to the edge, but then there would be some fall-off towards the edge. (It is extremely hard to directly compare the published MTF curves from different manufacturers, but my impression is that the Sigma curve indicates performance at least as good as the Leica APO-Summicron-M 50mm f/2 ASPH).

If you compare the measured MTF charts produced by ePhotozine using the same camera for each lens, the Sig50-2 pretty much matches the APO-Lanthar. The frame edges are about as sharp as the centre at all apertures. Note that this is at the distance you’d use to photograph a wall chart. At longer distances, Gordon Laing found it needed to be stopped down a little for the far corners to get completely sharp, although the centre was sharp from wide open (exactly as predicted by SIgma’s own MTF charts). Vignetting is inevitable with small fast lenses, but there’s no unusual problem with the Sig50-2, and it is better than the APO-Lanthar. Chromatic aberration is mostly better. A pile of reviews of this lens came out with its first release (for instance, here, here and here). Their only major criticism was the price. At around 620 GBP/640 USD, yes, it is significantly more than the Sony 50mm f/1.8, but its optics and build are much better. It is in the same price range as the older Sonnar, and several hundred less than the APO-Lanthar. In this context, the price is positioned fairly in the market. It represents a mid-price option, compared to the bargain 50mm f/1.8 under 200 GBP and the top of the range 50mm f/1.2 at more than 2000 GBP.

What finally convinced me about this lens was a comparison I saw on YouTube by Alex Barrera. He shot the Sig50-2 on an L-mount camera against the new Leica Summicron-SL 50mm f/2 ASPH lens which costs about 3x as much. (OK — Leicas have some characteristics of Veblen goods, so there is always a premium, but still…) He made the original raw files available (thank you!), so I downloaded them to see for myself. The Summicron is a very good lens, but I preferred the results from the Sig50 in every respect. If it is noticeably better than a Leica Summicron, then it is a terrific lens.

Sigma had a cash-back offer over the summer, so that was the incentive I needed. To cut to the chase: here is my Sig50-2 on my Sony. I’ll try to put up some images and first impressions in the not-too-distant future (no promises about how distant that is!).

Oh — and one final point. Very little of what I’ve written here matters. I’ve gone very deep down a nerdy rabbit hole in this blog. That’s just me: I have fun with the lens-geek stuff. You don’t have to. None of this matters as long as you find a lens that suits you in the way it feels in your hand, the way it operates and the pictures it produces. If your picture is interesting enough, no one will care. Did anyone ever care about the MTF curves for the lenses Robert Capa took with him on D-Day?