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PST solarscope - What does the blocking filter block?
I'm looking at my PST, I understand the Energy rejection filter at the front, and the etalon in the middle, but what does the blocking filter at the eyepiece end actually block?
They are horrendously expensive, especially larger ones like the BF15, just wondering what wavelengths they actually filter that the ERF and Etalon don't block.
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