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jetstream

Spot diagrams

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I ran across this paper by Celestron and am wondering how refractors and newts compare to the spot diagrams presented in the article. The Edge SCT looks pretty good.

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=0ahUKEwjgxMim3fzTAhViz1QKHV9lC-0QFgg_MAw&url=http%3A%2F%2Fwww.celestron.com%2Fmedia%2F1360271%2Fedgehd_whitepaper_final.pdf&usg=AFQjCNHzHBDg_lKZcrF6uz4u56mdKf2A-g&cad=rja

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Interesting article! Using the approach outlined, I imagine the spot diagrams for fracs and newts would not look very different, as each is the convolution of the Airy disk and diffraction rings, plus the seeing effect. Although the disk and rings for the frac would look slightly different, broadening it in this way with the seeing function would tend to minimise any differences between the scopes themselves, I imagine. The real difference would be with visual observing, where the seeing allows you to see the Airy disk and diffraction rings in moments of good seeing.

Chris

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Posted (edited)

Looking at the paper/artical would it be correct to say that only one set of "images" are actually photographic in nature - those in Appendix A, page 16 - the rest appear to be a computer prediction of the spot pattern formed. And as such not real. Basically it all appears based on a computer model of what should be occuring.

Being more then a little distrusting I would also expect a manufacturer to take say up to 25 scopes and select the one that gave the best results to take the findings from. Can you imagine turning up at FLO and saying you want to try out 10 Edge HD's and the one you think the best you will take?

Edited by ronin
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1 hour ago, jetstream said:

I ran across this paper by Celestron and am wondering how refractors and newts compare to the spot diagrams presented in the article. The Edge SCT looks pretty good.

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&ved=0ahUKEwjgxMim3fzTAhViz1QKHV9lC-0QFgg_MAw&url=http%3A%2F%2Fwww.celestron.com%2Fmedia%2F1360271%2Fedgehd_whitepaper_final.pdf&usg=AFQjCNHzHBDg_lKZcrF6uz4u56mdKf2A-g&cad=rja

Great article. I certainly found the 8" Edge I had for a while a very nice visual scope. Good flat field and worked well with Ethos eyepIeces.

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I'm thinking SCT's are misunderstood by many and understood by a few... I hope to join the latter crowd someday.

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Just now, jetstream said:

I'm thinking SCT's are misunderstood by many and understood by a few... I hope to join the latter crowd someday.

Certainly cooling SCTs is a black art I think!!

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I can still recall the views I got of Saturn about 6 years back when I had an older Celestron C8+. On one particular night the planet looked absolutely amazing - at 250x it reminded me of the Pioneer 11 image of the ringed planet :grin:

 

 

p91.jpg

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I had a similar experience with Jupiter back in 2003/2004, when a member of my local astro club was desperate to sell his old orange C8. He'd been listening to all the waffle about fluorite apo's by Vixen and Tak, and he'd decided it was time to "upgrade", (a term I hate!). He'd left his old C8 at the observatory for about three weeks in the hope someone would make him an offer. One evening, when we were all sat around having a brew and talking Tak, the C8 owner pleaded with us to just take a look through his scope. Reluctantly several of us went up into the big dome where the scope had been stored for the previous three weeks, we opened the slit and aimed the scope at Jupiter. That scope then delivered the best view of Jupiter I've ever seen. It's owner was totally stunned, not just by the offers to buy his scope but by the view itself, as his old orange C8 had never before given such a view, and hed had it since 1980. I never saw that C8 after that night as its owner grabbed his scope, loaded it into his car and took it back home with him. It had delivered one truly stunning planetary view in 23 years, but it was enough to convince its owner that the C8 was a very good scope. I've often wondered if it ever again managed to produce such a memorable view? I believe he still has the C8! 😊

Mike

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Always fancied one of the original orange C8s for some reason, not sure why.

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I think spot diagrams, those presented by manufacturers of telescopes, fall into the category of "don't believe everything you see". Years ago Celestron famously presented spot diagrams to show that a Schmidt-Cassegrain system was superior to other designs. They based this on a true Schmidt-Cassegrain whereas their commercial instrument was a variant.    :icon_biggrin:

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Posted (edited)

1 hour ago, Stu said:

Always fancied one of the original orange C8s for some reason, not sure why.

Me too Stu :smiley:

There is something about that orange and grey colour scheme that is a bit iconic:

 

page21_3.jpg

Edited by John
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It's hardly surprising that many of us lusted after one of them, I know I did. They graced the pages of S&T for so many years and at the time the only real alternative was a Questar which always seemed financially out of reach. I have to say that when I finally got to use very early C8's I was a little disappointed with the performance, however they gradually improved specially with the introduction of the SuperC8 and my up to date 8se is superb.    :icon_biggrin:

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Ade Ashford told me that his favourite SCT was probably the Celestron Ultima 8.

 

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