Nothing too surprising here. The f/1.4 is slightly faster and provides slightly more isolation when shot wide open. The f/1.8 is lighter and less expensive.
Given the outstanding ISO performance of today's bodies, the extra half stop may not be all that valuable unless you shoot a lot of dim, dark, or night subjects. And at f stops other than wide open the difference in performance is minimal.
And just to confuse things further, someone may chime in an suggest that the Sigma competitors are just as good — or letter — and less expensive.
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It's hard to imagine a true need for the f/1.4 given today's FX bodies and clean ISO 6400 performance. You have to be shooting the proverbial black cat in a coal mine to care about the light gathering difference between f/1.4 and f/1.8, and the difference in subject isolation is minimal if even visible at 50mm. On top of that the f/1.8 optically outperforms the f/1.4, as well as costing less and having less bulk.
And if I were going to buy a 50/f1.4 these days, it would be the Sigma anyway.
As for a better first prime, that would depend a whole lot on what you shoot. As a ridiculous example, my most used prime is a 400/f2.8 - in fact I shoot more frames with it than with any other lens. But you probably don't shoot the same subjects as I do, or for that matter, in the same conditions. Another entirely valid but unorthdox choice is the 60/f2.8 AFS Micro-Nikkor, which can double as a "normal" lens in the traditional sense of the word and is also obviously also a macro lens, if that's what captures one's interest.
For most folks, a better first lens is one from the set:
Mon 15-Apr-13 11:55 AM | edited Mon 15-Apr-13 11:59 AM by billD80
I used the Sigma 50/1.4 happily for years. It's a great lens, rather huge, but would look super on a D600!
Truth is, my Tamron 17-50/2.8 got more use than the Sigma. But the 50/1.4 is quite a lens.
BTW, if you stay with Nikon, you won't have any firmware upgrades to worry about. If you go with the Sigma, get one from a high volume dealer, as their stock is likely to have the latest firmware installed.
I tested both about 1 year ago. Difference between them, in my eyes at least, is not significant enough. The 1.4G has very shallow DOF as all other 1.4. The 1.8G AF faster. Both are reasonably cheap. If you can, go to your local camera shop and check them out.
I settled with the 1.8G because I care more about that tiny bit faster AF. Most of my objects are not that patient.
Out of all my current lenses (50mm 1.8G, 85mm 1.8G, 70-200mm 2.8G VRII, 16-35mm f/4G), this 50mm 1.8G probably is my most favorite lens.
I prefer the 50mm f/1.8G and use it more than any other lens on my D600. Both the f/1.4G and f/1.8G are hard to find right now, and some stores are selling them at prices higher than regular retail. Be sure you don't pay too much.
I have the 50 f1.8, not the 1.4. Everything I read prior to purchase said the f1.8 version AF's faster. I use it for indoor basketball, so AF speed is very important to me. The 50 f1.8G focuses fast enough for basketball. I would have paid the premium for the f1.4 if I could have determined that it AF'd faster.
In terms of IQ, there are so few instances when you need f1.4, and the DOF at that aperture is so small, I would almost always stop it down. Stopped down to f2.0 or f2.8, the IQ difference is probably non-existent. So,...save your money. My feeling is: if you have to rationalize why you need f1.4, you probably don't need f1.4.
IMO this is a similar question to the same one regarding the 24mm, 28mm, and the 85mm primes. The answer seems always to be: if you NEED the 1.4, GET ONE, and if you do not, then the 1.8 is so close in its range as to be hard to spot a significant difference. The only other consideration is bokeh, and in the case of the 50mm 1.4G, auto focus speed seems to be slower than the 1.8.
Someone else has a line that seems applicable: "even a SLOW Ferrari, is STILL a Ferrari".
I love my 50mm 1.4G, and have use for that aperture. Having said that, if I'd not bought it "used", then I'd have purchased the 1.8G. It IS cheaper and almost as good.