What Nikon lens to buy after getting D3100?

I just got my first SLR and want to go ahead and buy a sec lens. I want something that will be good when shooting at night.

And I'm debating with these three lenses: 50mm/1.8G AF-S, 50mm/1.4G AF-S or 35mm/1.8G AF-S. I would like to know what's the difference between the three, and if there's any other lens that I should consider as my sec lens please let me know and why should I get it.

Although I'm a Canon guy the lenses these two makers offer are pretty similar.

First the difference between the 50 f/1.8 and the f/1.4 is so minimal that it probably won't make any difference at all - after it's only 4 tenths of a stop. I have the Canon 50 f/1.8.It's a good lens but too tight for most applications that I've found. Those rare times yes great but in general not versatile at all.

The 35 would be a good night lens as well but still a little tight. But you're not going to find anything that's versatile with that kind of f/stop until you get into the really expensive lenses.

I use a 28-200 as an all around lens. I don't know about the Nikon model but mine is fast, sharp and accurate probably 99% of the time.

You might consider a lens that's quite a bit more money, the 18-200mm lens.

For scenes illuminated by nothing brighter than the full moon the AF-S lenses may not be the best. Unless you can find a bright object in the distance to lock on the autofocus, you can't focus accurately. The 35mm f1.8 AF-S has no distance scale. (Which is too bad, because it might otherwise be great in the dark, being sharp only slightly stopped down.) The 50mm AF-S lenses do have distance scales, so you might be able to turn on your flashlight and set distance to infinity. All of these will dial past infinity if you try to focus by feel. I like my Nikon AF-D 28mm f2.8 or Sigma f2.8 24mm (out of production) because they can be dialed in the dark to infinity. They are decently sharp at f3.2, which the Nikon AF-D 24mm f2.8 is not. Alas, they do not autofocus on the D3100.

For cityscapes at night, autofocus should work.

I have both the 50mm f/1.8 and the 35mm f/1.8 and love them both. For my work shooting NBA and NCAA basketball beneath the basket, I rely on the 35mm for capturing the fast action in challenging arena lighting. The 50mm is too close for my tastes, but I see other photographers using it regularly.

Off the court, I find the 35mm works well as a walkabout lens. The 50mm brings my subjects a bit closer, and works well for portraits.

Which one to chose? I'd suggest this. Zoom your kit 18-55mm lens to the 35mm setting, and keep it there. See what the world looks like from the 35mm point of view. Then do the same from 50mm. (don't cheat and go to 55mm).

The view that suits your shooting style is the one you should invest in.