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OAG at very long FLs
Wow. this is not easy. I am trying to eliminate elongation in stars from my imaging and have decided to go down the road of OAG'ing. But I'm using an EdgeHD14" SCT which means that I'm stuck with running at F11. This means a FL of 3900mm or so.
An OAG picks up stars off the edge of the light cone - hopefully a corrected edge but the way the thing has to be set up, the mirror in the OAG is actually only about 50mm or so from the back flange. The fixed distance from that flange to imaging plane according to Celestron is 146mm so the stars the OAG is picking up are not corrected. And at that FL, the imaging chip in a guide camera (mine is a QHY5) struggles to get me any decent kind of focus. I'm therefiore working with blobs rather than stars for guiding.
And at that FL, the graph looks like a lie detector on a politician.
Can anyone offer me any pearls of wisdom in the art/science of guiding at this FL?
Peter
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