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Headshots and full-body - both indoors (studio lights) and outdoors.
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The 180mm is not going to serve you well indoors unless you've got a very long space in which to shoot. For full-length shots (say 6' of height) you'd need to be about 35'-40' away from your subject if you're shooting digital. For a headshot you're going to be about 12'-15' away from your subject. Outdoors isn't a problem from a space standpoint, but it's kind of hard to work with and direct a model when you're 35' away from him/her.
I think you would be better served by something in the 85mm or 105mm range. From Nikon, there are the following:
105mm f/2 DC (de-focus control)
105mm f/2.8 Micro
I've used all 4 lenses at one time or another. A lot of people like the 85mm f/1.8. It's inexpensive and sharp, a real good lens for the money. But It's not a personal favorite of mine. Specifically, I really don't like it's bokeh characteristics. Bokeh is the look of out-of-focus elements in your image. There are a couple of good articles here
if you're interested.
The 85mm f/1.4 is really outstanding. One of my favorite lenses when I still shot a lot of 35mm format. It's also more than you're looking to spend. If you can find one used in your price range, grab it, run, and don't look back.
The 105mm f/2.0 DC is an interesting lens. It allows you to control the bokeh effect. It's primarily a lens for portrait photographers who use it to soften an image. It's also more than you want to spend and kind of a niche product.
The 105mm f/2.8 Micro is a very sweet lens. It's really sharp, exhibits good bokeh, and is in your price range. Being a macro lens, you can focus very close if you so desire. It's great for tight head shots. It might be a little long for full-length shots indoors on a digital body, but it would certainly be a better choice than the 180mm for the same kind of work.