Someone mentioned the Thambar, a lens which I have yet to see "in the flesh" but, I am told" gives unique portraits because it is. "Acceptably soft" and has a central stop mounted on a clear filter. I am also told that mirror lenses have terrible bokeh because the have the central mirror. For portraits that are "old school" I use an uncoated 135mm Tessar taken from a medium format Mentor camera. I have tried making a central stop by supergluing an old button battery onto a UV filter... it's a cheap Thambar. I can't say it made any difference. The "golden hour" available light does though.