Hi Christian, did you ever think about building a Gregorian? Could be interesting. CS! Bart.christian viladrich wrote: ↑Tue Sep 17, 2019 8:14 am Hello Valery,
Going back to the initial question of this post, and after the tests recently done à St Véran, I agree that the combination of a large ERF and a reflecting telescope is the best HR solar telescope in large diameter.
The Cassegrain configuration is indeed very attractive.
Best regards
Christian
What do you think is the most versatile high resolution solar telescope design?
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Re: What do you think is the most versatile high resolution solar telescope design?
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Re: What do you think is the most versatile high resolution solar telescope design?
Would love to know more about this.langleif2 wrote: ↑Fri Sep 20, 2019 1:08 pm No one seems to make a suggestion for a "work-around" solution to the sphero-chromatism inherent in the Schmidt plate. Of course, custom solutions are there, but rather too expensive. In my stores I found a so called apo Barlow I never found any use for. It's a triplet with an air gab, a cemented part and a third lens. The air gab is tiny so there's really only one option - to increase the distance between the two lens arrangement.
With the modified barlow and looking on a star test in a refractor optimized in green as they usual are, I found a "nice" undercorrection. Not doing any calculations (I can't) I don't know how much, but I can increase the distance 4-5mm step by step and further experiments will show how much better or worse. There's no astigmatism seen so far. I need to do the same experiments with the SCT, I don't see why it shouldn't work. And of course, it's not only the Sun also Venus will be better.
And it does work! You won't believe it when you see it, from a mushy, blurred sun also affected by the seeing to a tack sharp video at least seen on the screen. Even the seeing calmed as was there some kind of relationship with the corrected optics. I recorded the video in the afternoon within 15 minutes, the mushy one with a normal Barlow, the other one with the corrected Barlow, 2 minutes each, 1800 frames with my trusty DMK41 camera that can only do 15 fr/sec. 300 frames were stacked in AutoStackert and sharpened a bit:
Very best,
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Re: What do you think is the most versatile high resolution solar telescope design?
Very interesting, I'll have to look around for a triplet barlow. I assume you're talking of using a 2x? Any particular suggestions of known well working ones for this?langleif2 wrote: ↑Sat Sep 21, 2019 7:32 am Hi, Marty
It's really straight forward. All information is given. You can use all triplet barlows with an airspace. However, the magnification will depend on whether it's a long type or short type of Barlow. You just need to increase the airspace about 8-10mm or so at least for the long type. I did this placing the cemented lens part in a filtering and used another filterring as a spacer to the main container for the third lens as seen on the foto.
This will generate a severe undercorrection suitable for an 8" Schmidt plate to match the wavelength of CaK. By undercorrection the SCT will have it's optimum in the blue end and not in green as newer SCT's or yellow/red end as some elder SCT are optimized. Of course, you don't wanna use this Barlow for H-alpha or for the nightsky. That'll be detrimental, but for Venus it will do just right as well.
Very best,
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Re: What do you think is the most versatile high resolution solar telescope design?
Interesting, thanks for sharing. It would be useful to know which brand is the Barlow you used because not all triplet barlows are equal. The spaced element of many triplets is a converging meniscus which is used mainly to correct the divergence of the marginal rays. However other triplets - some GSO barlows for example - have a different design.
Raf
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Re: What do you think is the most versatile high resolution solar telescope design?
Thanks for the detail. Unfortunately that Meade barlow is now difficult to find except in the used marked but I will try anyway.
I tried yesterday to modify an airspaced meniscus Barlow but results were disappointing, no gain in contrast compared with the barlow in the original configuration. May be that the design with the meniscus doesn't work this way.
I tried yesterday to modify an airspaced meniscus Barlow but results were disappointing, no gain in contrast compared with the barlow in the original configuration. May be that the design with the meniscus doesn't work this way.
Raf
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Re: What do you think is the most versatile high resolution solar telescope design?
Very interesting indeed.
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!
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Re: What do you think is the most versatile high resolution solar telescope design?
I literally just bought a Meade 4000 series #140 triplet barlow.
Will experiment and report soon.
Very best,
Will experiment and report soon.
Very best,
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Re: What do you think is the most versatile high resolution solar telescope design?
So going a ways back in this thread here's the four element ~ 3.5 x UV Barlow corrector designed for the Celestron 9.25 by H. Rutten (yes, that Rutten), and it uses simple plano convex & concave COTS lenses which can be sourced from Edmund or other vendors. It might work well for other SCTs - especially if you can use OSLO to re-space the elements a bit to re-optimize the correction.
https://www.astrosystems.nl/uv-barlow-
Seems to be a fairly straightforward build...
https://www.astrosystems.nl/uv-barlow-
Seems to be a fairly straightforward build...
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