A 150 mm f/7.5 Petzval design: http://users.rcn.com/rflrs/Ptz07-79x.atm http://users.rcn.com/rflrs/Ptz07-79x.len http://users.rcn.com/rflrs/Ptz07-79x.txt http://users.rcn.com/rflrs/Ptz07-79x.zmx Only four air-glass surfaces.