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I owned an FS152 for years, it was my first expensive astro purchase.
It gave even to this day some of the finest visual views I have seen.
Fluorite doublet is a good formula for visual if not for imaging.
It would cooldown in no time and I was blown away by the initial views when I first got it. They were way brighter than I expected.
I haven't looked through a lot of Dobs but the guys point makes sense to me. Compound scopes are vulnerable to tube currents (micro seeing environment) that affect their ability. I had a long discussion with Anthony Wesley about this at Parkes and he has the same view on this. He of course is at the very top of his profession so his views are valuable.
6 inch refractors are also renowned for cutting through the seeing. Mike Sidonio and Marcus Davies both image with 6 inch refractors and they continually show how these high end APOs can cut through the seeing etc and it takes a far larger scope to outperform them. Even then that would be more affected by the seeing.
So much so that Roland Christen has said at times that the sweet spot for scopes is a 6 inch refractor.
The FS152 would be far less affected by the heat issue and that is the guys point.
Greg.
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