I forgot to jot down my thoughts on observing briefly back on 9/27/20 with my 8 inch f/6 newt. I started my evening by setting up the 8 inch f/6 newt, collimating carefully, and letting things cool down for 2 hours. I decided to throw a hail mary and use the 3mm Delite eyepiece resulting in a 400x view of Mars. For maybe 5-10 minutes, the view was contrasty and well-defined as the seeing seemed to be above average. From what I remember, Mars was still in the east and I was very surprised at the wealth of surface detail. (Usually the seeing to the east is below average to awful.)
I also scanned the moon and I was able to see the kind of detail that I usually see from the C11 through the barlow and QHY290m.
But after awhile, the image started shimmering and shaking and the magnification was clearly too much for the seeing conditions.
Part of the reason for setting up the 8" newt was Venus. My excitement was based on a theoretical notion that since the 8" f/6 was a two mirror system, there would be much greater UV throughput. The C11 has two mirrors plus a corrector plate that obviously has anti-reflective coatings on it. Also, the corrector plate itself could be a bad transmitter of UV light.
I collected some RGB on Mars and it was pretty disappointing. The seeing was below average and surface detail was not well defined at all. Usually with the C11, I can see a few scant moments of decent detail in below average conditions. But not with the 8 inch. This runs sorta counter to a lot of received wisdom about aperture, seeing and the size of your scope.
This is a screen shot of the best moments of a single video from the C11 on 9/30/20 on the left and 8 inch f/6 newt 9/27/20 on the right. In fact, I'm even cheating a bit on the right by shooting through the Baader 685nm IR passthrough filter. The right image should be a lot more contrasty. It's also worth mentioning that I had to lower the FPS to deal with the loss of brightness through the smaller instrument. So my chances of getting a few "lucky" frames were much lower in the 8 inch. Much less barlow power would have been useful to keep the FPS high, but that would have meant something like a specialty 1.3x barlow.
Perhaps no fair conclusions can be drawn from the image above and the evening in general. It is quite possible that the C11 would have just produced a larger version of the poorly detailed image on the right. But what is certain is that the theoretical maximum amount of detail will always come from the larger scope so there's not very many good reasons to use the 8" over the C11.
Later, I was able to test my theory about UV transmittance. The seeing continued to be poor into the early morning hours. The video through the Baader UV filter, QHY290m, and the Siebert barlow was also poor. Not a definitive test by any means, but it didn't look like I was getting much UV at all through the 8" f/6. To be fair when seeing is below average, it's hard to see any UV details on Venus with the UV filter. I was expecting some obvious difference but none appeared. It's quite possible that the coatings on the 8" mirror don't transmit UV signal well; or that there is enough deterioration of the coatings that the UV transmittance has been compromised.
This is one of the better frames of early morning Venus on 9/28/20. There is some north and south brightness and hints of larger, darker structure of the equatorial areas. But most frames were just misshapen blobs of uniform brightness.
(Later: I was looking at more video from the 8 inch and there is a consistent "fuzziness" (or scatter) in the images which make me wonder if there is an optical defect like a turned edge. It doesn't jive with the 400x views I had early in the evening, but sometimes very good seeing fixes a lot of problems. Hm...)
(Later, later: I think there's a good chance I FORGOT to place the UV/IR filter in the camera for the color data.) 👾🔥😓
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