Would these older orange C8's have about the same light throughput as one of the modern Celestron SCT's with XLT coatings?
I'll do a side by side with my friend Pete who has a modern coated C8 as soon as possible. In my opinion though, I'd be more concerned about optical quality. One thing my friend Steve mentioned which I've mentioned in the past is that an observers perceived contrast may be increased because the background may appear darker because there's less light coming in. But I wouldn't get too wrapped up in all this. The images are very bright! For example in this review the coatings appeared to make a difference, but the winner in this comparison had the coatings which were less enhanced. https://www.cloudyni...y_scopes_1.pdf
Think about it another way. If light isn't concentrated where it's supposed to go, then there's light loss that way as well, so I wouldn't take coatings too literally in this particular case. Even with modern apos, there's so much hype about FPL-53 glass. Whenever observers obsess over this, it's a red flag in my experience because they're more obsessed about glass and almost completely oblivious to figure. My friend Darren has used about three dozen different SCT's, maybe more and no matter how many times I test them, I've just never been that excited. I've never seen one that's very special. This old telescope here is special in my opinion because I've used and tested many great telescopes in world class conditions and this stands up.
In my mind, I'm always thinking about the best images I've ever seen and those are the images I'm always comparing. In my opinion, this is probably the finest 8" sample I've ever seen. It's really that good and several observing buddies of mine were flabbergasted, myself included. One of my friends had a 7" F15 Zen Mak Cass set up near he and I both agreed this C8 delivered finer image contrast. We even had a SkyWatcher 150 Esprit and it was standing up with that as well on Jupiter. Wonderful colors and surface detail were visible at various magnifications. There was also an 11" SCT next to us as well and that wasn't holding up as good an image as this C8 was on Jupiter. That's an example of extra light gathering but the contrast just wasn't there. To me, it's a testament to the integrity of the instrument. Although I've never been a fan of SCT's because of previous experiences with them, I still whole heartidly believe that most common optical designs, if made properly, have the potential to deliver world class images.
Edited by Daniel Mounsey, 28 June 2017 - 10:55 PM.