An inexpensive one at that! I know I'm asking for much, but I have an astro project idea for a fixed focus (infinity) 4x5 camera housed in a steel tube. The faster the better, and coma will be an issue when shooting stars. Right now I am leaning towards a Tele Optar 15" f/5.6. I have heard that it was a pretty sharp lens. How well do you think it will perform wide open?