150mm MCT f/13, 31% CO
"People say I'm in denial. I disagree."
Friends call me Duane. Compustar C14, Leo Henzl's Custom C8, 6" Refractor Adv. GT mount, 6" F5 Omni XLT Newt., LXD-75 F4 Imaging SN8, Meade 8" F6 Newtonian, EX Dynamax DX6, RV-6 ETX-90 Astro, Meade 2045 4" SCT, B&L 4000 Vixen/Celestron 80mm F11 JC Penny 60mm AZ/ALT Refractor Binos 25x100
Quote:As I mentioned, this zone is quite common on larger Celestron scopes. I doubt that by itself it does any meaningful harm, but that is only by itself. It all adds up though. If there are no other issues (TE, SA, Roughness, etc) then the zone won't matter.But all to often, these other errors do show up in Celestron (and Meade) SCTs and again, usually none of them is serious by itself, but because they all add together, it turns them into scopes that vary widely in quality.Most are good to very good, and many are downright excellent.Some though are only passable, and honestly, I can't say I have ever seen a truely bad one. But the problem is that assessing the quality when multiple errors exist is complex. You have to measure each error then approximate the damage to the MTF curve which is then added to the curve from the other optical abberations.SA is the major killer in an SCT though, if it is bad enough. And it is rarely that bad, but if it is in the middle and there are other problems (roughness, zone, turned edge, etc) it makes for an SCT that has some more easiy reduced contrast performance. Enough that a good observer will see the differnce.
Thank You, Matt - Astro-Video Systems http://www.astro-video.com/ Home of the NO AMP-GLOW Astro Video Cams
Quote:Actually, the were indeed designed for imageing. The best performance is at about 4" of back focus.
Quote: These scopes were not designed with imaging in mind...
Quote:Actully, you said: Quote: These scopes were not designed with imaging in mind... I was responding mostly to this statement.
Quote:Well, I apologize for any misunderstanding on my part.