Having had 3 Newtonians in the past ( 6" f5, 10" f5 and lately but already sold 8"f5) I always got a little disappointed at the image quality when the magnification was pushed above 70x. I could never reach pin sharp focus on bright stars. The planets looked a bit fuzzy, and in good seeing, even though I could see the Cassini Division easily for example, I could always just tell I am looking through a Reflector. I used cheshire and lasers to get a spot on collimation and star test after, but still, it was never that good, even after letting the scope cool down.
So After deciding to get the 120mm f8.3 Refractor to be my only scope, I liked the image quality much better, and the CA didn't bother me too much, expect on bright stars and Jupiter.
Still, a 120mm is a 120mm Aperture and I missed deep sky performance of the larger apertures, especially on Globular Clusters. Having used the Refractor for a couple of month, I decided to finally give a try to the mighty 8" f6 Dob (Skywatcher). To say I am surprised is an understatement.
Last weekend, the 3 of us picked a dark sky site at the my friends little garden with fences. Bortle 3/4ish. Both the seeing and transparency was average. We have waited the planets to come higher up in the Sky. We Picked Altair in both scopes, and I did a quick Star test on the dob to check collimation, since it was an hour and half drive to get there. Star test looked good.
First Target was Jupiter, and all 3 of us could see a major difference. Jupiter was pin sharp at mag 70x, 150x and 225x. Even though the planet was floating a bit due to seeing conditions, we could easily got that snap of sharp focus. After we checked Jupiter in the Refractor, all 3 of us agreed that it looks much better in the dob. Next Target Saturn. Same story. In fact, it felt like you are looking directly at Saturn without anything in between. It was super beautiful and clean. Cassini easily spotted and so the cloud belts. After admiring the beauty of the planets, we went to check the bright star magnification test. At 70x, where the other reflectors started to show a bulky star image, I could still snap the focus to get pin sharp image. At 150x, It wasn't that sharp anymore, but still better than the other 3 was at 70x. After that, we went to check large open clusters with a 2" 40mm eyepiece and all 3 of us agreed again, its all better in the dob. We did check on galaxies too, but personally, I couldn't see any difference. Galaxies are needy targets and screaming for excellent transparency and darker sky. All other DSO, planetary and Globular were noticeably better of course in the dob, in fact, the globulars felt better than they felt in the 8" f5 before, noticeably sharper pinpoint stars.
How is this possible? Could it be just a well figured mirror, and one can have this dramatic difference in these Chinese mirrors? Or did I have bad luck with the other 3? Just to note, the 6" f5 back then was bought brand new with a perfect collimation, but it was nowhere near this good in terms of image quality even in good seeing.
Knowing that mirrors can be this good, I would really want the 10" dob again, but I am afraid, I would get a so-so optics again.