Some of the best 50mm lenses ever made have been f/2.0 —
So true. The favourite 50mm lens of my career is the Nikkor 50mm f/2. It was sold as a 'budget' alternative to the f/1.8 and ( in those days ) very expensive f/1.4.
Well like you do, I thought the four times more expensive f/1.4 Nikkor must be better, so I saved up for one. For years I was completely baffled as to why it wasn't as good as the f/2 lens ! Fortunately I hadn't traded the f/2 one in. I ended up trading the faster lens for something else.
So if we got an f/2 50mm STM lens that was as good at f/2 as the 40 pancake is at f/2.8 I'd be in there.
Well all this talk of a possible new 50mm lens of f/1.8 to f/2 got me thinking about one of my few Nikkor lenses that I have left; the 50mm f/2 Ai-s.
As I said in the quote above, I remember this lens as being the best 50 I ever used. I remember spending ages puzzling over why my nice new, shiny and expensive Nikkor f/1.4 wasn't as good.
So true to my word I bought a Nikon : EOS adapter and gave it a go, having first had to cut the rear peg off before it took the mirror out of my camera. Well I wasn't looking back at the past with rose tinted glasses, this lens is superb from f/2.8 onwards, easily matching the potential resolution of the 5DII sensor. It is slightly sharper than the Canon 1.4 lens at these apertures, but much more so to the edge of the frame. At f/2 it is 'dreamy', but in a very attractive way, and I think the bokeh is quite interesting.
When making a lens that is really stellar at mid apertures it is much easier to achieve this with a lens that is slower to start with. This Nikkor f/2 and other lenses such as the 40mm pancake are examples of this. So if Canon were to produce a new 50mm f/2 lens it could well be stunning for a very reasonable price. I'm really hoping that we get a 2015 version of this Nikkor f/2. IS as well if they can keep it this good.
I've attached two pictures. The first is at f/2 + a little fill, softened with tissue, though of course this lens doesn't give any information to the flash, so
fill was a little erratic. I like what the lens has done here.
The second is a hand held snap at f5.6 and this picture gives an idea of the contrast the lens help to give. This is pretty well straight off the camera, tweaked in levels and the only sharpening is USM : 100% @ 0.4 pixel. The third picture is a 100% crop.
The only time I have used this lens on FF digital before was when I tried the Nikon D800. I now realise that one of the pluses of that camera wasn't actually the camera at all !
So the moral of the story is if you want a reasonably priced lens that is razor sharp after one or two stops in don't make it too fast in the first place.