For sometime now I have been planning to make a double stack module for my PST mod. When I recently acquired another etalon, upon amassing all the necessary adapters and bits I was ready to go. I had tried this previously but had been plagued by both reflections and sweetspotting issues. However since then have given the matter much thought and between the 2 etalons had make sure there were antireflective coatings a plenty. It took me some time to get both etalons working as an effective double stack unit, they both have to be rotated to their optimum position relative to the OTA, and then also rotated to optimum position to each other to throw reflections and to achieve an even image. Despite the worst conditions possible to do this - fast passing clouds and rain showers, I was pleased with the results I got. With this in mind the next step is to 'clock' the etalons with respect to each other so that optimum performance can be achieved quickly when setting up. This shot was taken with the 100mm at 1600mm focal length with the DMK31 camera.
