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It's a Starizona APEX x0.65 reducer. Which would make your f/5.5 a f/3.575 for the 100ED, or the 120ED down from f/7 to f/4.55.
So what I'm trying to understand now is how to compare the 100ED to the 120ED, as they both have different apertures and different f numbers. While the 100ED is faster at f/5.5, the 120ED has a larger aperture but its f/7. If both scopes had the same aperture this would be easy of course, but hunting for a formula now to properly compare these in assumably photons per second, or something similar (for the same light source and same camera sensor).
Last edited by Emuhead; 09-05-2020 at 11:13 AM.
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