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"Roland then set out to make the ultimate astrograph. It was the first "EDF." It used the StarFire design, but with FPL-51 with an airspace. With a 4-inch field corrector and focuser, it took some of the most impressive widefield astrophotos ever taken. The 152mm f/7.5 EDF ($6400) was the first apochromatic telescope that I had ever seen that was completely color free -- even out of focus."
Thomas Back - A Brief History of Astro-Physics Lenses
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