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The images I've seen suggest these blooms are light from a bright star just outside the field of view being reflected into the focal plane, but there are several candidate sources of the reflection. In particular I suspect it comes from something with a machined surface.
1. The central baffle - both outside and inside surfaces.
2. A machined edge around the perimeter of the secondary mirror cell, with the light reflected in much the same way as glancing incident light will be reflected off the sides of those lovely "handgrenade" eyepieces from Meade, Vixen and others.
3. Circular baffles inside the OTA - assuming there are some.
4. Could even be coming from a reflecton off the inside of the last bits of tubing coupling the camera to the scope, if any of them has a machined surface - even if its black anodised its still shiny enough.
I think the vanes supporting the secondary could be ruled out.
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