Blurryeyed wrote:
It is all about the working space, and perspective, the longer the lens the flatter the image, you also have to consider that with a 135mm lens you have to stand back quite a distance to get a full body shot and even further for a group shot, the shorter lenses tend to elongate your subject's features, personally flattening or elongating has never been a big issue for me, but I am not a pro.
Below is an image created with a 500mm lens which came out just fine.
I find a 85mm lens on a crop sensor camera ideal for head and shoulders shots, but I wouldn't use it for a full body or group shot. When we talk about portrait lenses, we need to specify what kind of portrait we are talking about. There isn't a single focal length appropriate for all kinds of portraits.