Good portrait lens for d3100?

I have a nikon d3100, i want to buy a 50mm f1.8 as i portrait lens, but some tell me that a 35mm would work as a 50mm on my camera and someone else told me to just set my 18-55 kit lens on 35mm and thats what the 35mm lens would look like, is that true? Would you recommend the 50mm f1.8 for me to shoot portraits with? I'm a makeup artist so i'm trying to find a good lens so i can take good pictures of the makeup. Thanks!

Added (1). I don't mind that it doesn't autofocus, i like to manual focus anyways, thats what i do with my kit lens.

35mm/50mm/85mm

but the question is, would a lens really help… Cos you need to know what you are doing with the equipment first… As well as the light…

On a 35mm film camera or full-frame DSLR a focal length of between 85mm to 105mm is considered an ideal portrait focal length. Since your D3100 has a 1.5x "cropped sensor" a 50mm lens on it will have the angle of view of a 75mm lens on a 35mm film camera or full-frame DSLR. So for portraits a 50mm lens works well on your D3100.

On a 35mm film camera or full-frame DSLR a 50mm lens is considered a "normal" lens since it approximates the angle of view of the human eye. The 35mm lens on your D3100 will have the angle of view of a 52.5mm on a 35mm film camera or full-frame DSLR. So the 35mm lens would be considered a "normal" lens on your D3100.

Now the bad news: Because Nikon chose to not put a focusing motor in your camera body only the more expensive Nikon AF-S lenses will auto focus on it. So instead of paying a mere $120.00 for the Nikon AF 50mm f1.8 you'll have to pay $435.00 and buy the Nikon AF-S 50mm f1.4 lens. The Nikon AF-S 35mm f1.8 will auto focus on your D3100.

Since you are wanting to take pictures of makeup I suggest a third alternative: the AF-S Micro Nikkor 60mm f2.8G ED. This lens will allow you to get closer to the makeup and since its angle of view is the same as a 90mm lens on a 35mm film camera or full-frame DSLR it makes an even better choice for portraits than the 50mm lens. $599.95 at http://www.bhphotovideo.com/...ovideo.com

It is true that a 35mm lens would work on your camera as a 50mm one would work on full frame or film cameras. That's due to the crop factor.
But on full frame or film one would use 85mm lenses for portraits, not 50mm ones. So a 50mm one will be the correct choice for your camera, as that will work like a 75mm one on full frame/film, which is close to the traditional 85mm there.

The crop factor is only relevant to you if you compare focal lengths across different sensor or film sizes. One lens set to 35mm will give you the same angle of view as any other lens set to the same focal length when both are mounted on the same camera. So don't worry overly much about it.

Anyway, no, the 50mm/1.8D AF will not be a good choice for you. It's a fine lens by itself, but it's not an AF-S lens, just an AF one. This means that it will not autofocus on your camera as it does not have a built in autofocus motor. You will need the 50mm/1.4G AF-S, which unfortunately is much more expensive (but also better).
Be careful, there's also a 50mm/1.4D AF, which won't autofocus on your camera either.

It's not a good time to buy lenses though, as they have taken quite a price increase due to the catastrophe in Japan. The 50mm/1.4G should normally cost about $360, but now it sells for far beyond $500.

Edit:
Then get the 50mm/1.8D. But… Manually focusing at f/8 or so is one thing. Manually focusing at f/2.8 is an entirely different cup of tea, it's much more tedious and less forgiving of errors and camera movements. Your model will have to set very still and you will have a hard time keeping the correct distance. That's something i'd recommend that you try out at a camera store before you buy the 50mm/1.8D.