Both 85mm or 105mm (or 100 for non-Nikon users) or their equivalents based on format are fine for headshots though I prefer the 105 over the 85. For outdoor headshots I often use my 180mm f/2.8 at f/4 to throw the background completely out of focus, If you are cramped for space the 105mm might be a little too long so the 85mm might be your better bet. Just remember, the shorter the focal length, regardless of format, the more perspective distortion you will get. A "normal" lens, especially on a DX is in most cases a bad choice, as it will accentuate things closes to the camera, like nose, chin and brow.
Crop in the camera as best you can. It is considered good composition to place the eyes at the level of the upper third of the image but nothing is set in stone.
If people don't scare you, an 85mm (on a full-frame camera) is a good distance. I look to connect with the client. So being close is a good thing. I typically start out with a 50mm. I generally don't use those photos, but I use the proximity to the client to build rapport and a sense of comfort (for them). Then I use the 85mm and if things are going well, the 135mm.
Stoke-on-Trent, England, United Kingdom
On crop I found 85mm to be fine and my favourite from film, the 135DC, to be too long. On film and FX I find the 85mm to be too short, 105 to be 'ok' and 135 is back to my ideal choice. As soon as I get out the 645 this all changes
Admittedly, I did not read every single post but since I won a 85 2.8 and worked with a few other brands than my own part of the big deal about the lens is it's superior build. Nikon, Canon, Sigma all make their 85mm with the best possible glass and the simply produce a far superior quality of sharpen, and quality that zooms cannot match.
Check out test on these lenses on review sites like dpreview.com and other and all the results demonstrate the fantastic quality of not just the light but the color and sharpen over virtually any zoom lens and when used at the right height on a full frame camera there simply is not a better lens in most lines of lenses.
Yes there are a few 50mm 1.2 or 1.8 lenses but most of it's gain in popularity is really based in price and people will always argue they have made the right investment and that the 50 is good enough. It's a standard among semi-pros although many working pros use 50s too.
I use my for wedding and product work as well as head shots and it simply is the best lens I own when used as intended.
Caveman Creations wrote: If using a 50mm on a crop-sensor, it will only give you the "field Of Veiw" of an 80mm, not any of the other attributes. The 50 will not compress the background, and the Bokeh may not be as OOF. A 50 is a 50, no matter what it's on. An 85 is an 85 just the same. Now...
I use my 85mm in studio religiously. I can frame what I need to frame without being a country mile away from my subjects. I can do headshots, that are fairly loose, because it's closest focusing distance is about 5 ft. I like that framing, and I like the distance it puts me to the subject. If FOV is your biggest concern, then yeah. I'd go with the 50, because you are not going to get as much in frame with the 85 at the same distance. If you want background compression, and awesome OOF bits, then the 85 or longer is the only way to go. You just have to back up more!
If I am just shooting head and neck, an 85 is good but there is still a tiny bit of wide distortion since the subject is close. I find a 135-200 range is that much more flattering. The shorter the focal length the more it will exaggerate perspective in the face making the nose (center) larger and the ears smaller. I personally find 85mm very acceptable but just on the border.
If yo have a great 85mm lens on an ASPH sensor, go for it! You will get great images.
One advantage of a quality 85mm prime is that the focal length works well for both head and full body shots so you can stick with one prime and zoom with your feet.
Herb Ritts used a Mamiya 150 on a medium format body which had a similar equivalent focal length and he just zoomed in and out with his feet.