Double Stack Filter for Lunt 80 mm & 100 mm Universal TelescopesSFPT Internal Double Stack Module For Lunt LS80MT & LS100MT Universal Day and Night Telescopes. Now with new generation etalons every unit individually tested on Lunt's precision metrology equipment. Every specification is verified, not estimated. The SFPT is the internal double stack module for Lunt's 80mm and 100mm Universal Modular Telescopes. It adds a second precision etalon inside the telescope body, reducing combined system bandpass from 0. 45