What is the ideal focal length for a portrait lens?

The goal of your answer is to showcase an in-depth knowledge of the technical aspects of photography.

Focus your answer on the ideal focal length for a portrait lens and explain why it is the ideal focal length. You should also speak about the ways lens choice can affect portraits.

The gold standard for a portrait lens has been the 50mm. That said, many photographers prefer 85mm. The 50mm is great for the waist up, and the 85mm is better for a headshot. It depends in part on how close you want to get to your subject. You are going to be closer to your subject with a 50mm, and that could be off-putting for some people. I also think a prime lens is better for portraits than a zoom lens. Prime lenses have less glass in them and can help you achieve sharper images.