I found an article on CN that explains the bright star "bloat" we are seeing.
I think Glenn was right in his first assessment.
Look at figure 13 in below article in below link on "stray reflections". Identical to what we are seeing.
IMO, problem is filter or glass cover of CCD. The reflection happens within the glass due to extreme brightness of F2 image. A camera without CCD glass cover wouldn't get this "stray reflection". Perhaps anti-reflective glass cover would fix it. I think, as a test, trying a moon filter should eliminate all stray reflections.
"Stray reflections. On it’s own, the HyperStar is free of stray reflections; however, if you add any filters to the system, it is possible to introduce significant stray reflections around bright stars. Figure 13 shows how these stray reflections are formed, why they are so large, and what they look like. Of course, this is the exact same problem that will occur with any other fast optical system when the filters are used in a converging beam. The size of stray reflections can be reduced by using very thin filters and by placing them as close as possible to the focal plane. However, placing the filters close to the sensor will increase the brightness of the stray reflections. Another strategy is to move the filters so far from the focal plane that the intensity of the stray reflections becomes negligible. The problem with that strategy is that it requires very large filters. In the HyperStar adapter, the filter position is fixed so you get what you get. In my experience, it is probably best to use the HyperStar system without any filters."
I don't think so, Charles. Why wouldn't get the same thing with Hyperstar? I used no filters, and the Lodestar has a glass cover, but it's right up against the sensor. I have never gotten any reflections off of it. The Starizona article I posted explains what's going on. Without more correction, the SA causes much of the light to be unfocused. It's so unfocused that it starts focusing the central obstruction and cable. If I try to focus the bright stars, the dim ones go out of focus. The brighter stars show up more because the unfocused light is dimmer. Smaller stars have the SA, too, but it's too dim to show up. Even the nebula has a softened look to it because some of the light is unfocused.
IMO, when we focused on bright star, we were actually focusing on the reflection which defocused all dim stars. I maybe wrong, but I think a good experiment would be to look at a bright star field like M16 with a moon filter or some dark colored filter to dim incoming light. If all the halos go away, I'm right, if halos remain I'm wrong.
Your link shows spherical mirrors inherently have spherical aberration, but later mentions the corrector takes care of that. No doubt there is some spherical aberration at point of Freestar, but I don't think we are experiencing it yet as reflections overwhelm everything else.