The main reason I say this, again, is because the 50mm focal length simply does not create enough compression. That lack of compression creates perspective issues and introduces unflattering distortion, especially in head/H&S shots. The other issue is working distance. To get good H&S portraits with a 50mm you need to be about six feet away from your subject and that's simply not enough. It's awkward for the photographer and it's too "all up" in your subjects personal space. Using an 85mm you should be able to get good H&S shots ten or twelve feet from your subject; a much more comfortable working distance for all.
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I fully agree, the one important thing for portrait lenses is to
choose the lens that lets you stand at least six feet away. Eight or ten feet is better. Four feet is too d*** close.
Standing closer than six feet causes perspective distortions (noses appear too large, etc), and there is simply no reason to do that to your portrait subject. The subjects won't like the results.
105mm was classically considered the portrait lens for 35mm film, because even for head and shoulders, it simply forced standing back that far. The DX equivalent is 70 mm. Of course, we do need a wider lens for full length portraits, and of course groups, but the rule ought to be
"always stand at least six feet back". This, and the view that you seek, determines the lens focal length you need to use.
The word portrait can mean many things... from tight head shots to standing full length, or even groups. Use the lens that simply gives the desired view when you always stand at least six feet back. Eight or ten feet back is better.
With camera up on end in portrait orientation, a lens with 35mm focal length on a DX camera at six feet has a frame view of four feet. Is a four foot height of view your goal? If not, you need a longer lens. 60 or 70 mm will be better for "waist up" portraits. 70mm DX has a portrait height view of two feet (standing at six feet).
Here is some good information:
https://www.photoflex.com/liteblog/...he-face-controls-perspective-a-lighting-tutor
Two clarifications it needs:
1. This shows a "35mm camera", i.e., FX. A DX camera equivalent would be a shorter lens, this focal length / 1.5 (i.e., 70mm DX or 105mm FX).
2. The lens focal length does NOT determine perspective. The lens merely shows what it sees.
Where the camera stands is what changes and determines perspective (how large the noses look, etc, and at least six feet is a good thing).
The lens focal length merely determines where the camera has to stand. Use the lens that allows you to stand where you need to stand, at least six feet back for portraits.