What do you think is the most versatile high resolution solar telescope design?

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MalVeauX
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What do you think is the most versatile high resolution solar telescope design?

Post by MalVeauX » Fri Sep 21, 2018 3:26 pm

Hey all,

I'm curious what everyone thinks is the most versatile high resolution telescope design for solar imaging application.

There are solar newtonians, SCT's and of course the refractor (for common air spaced and mirror designs). However, I'm curious about which design is ideal for different wavelengths for solar imaging, mainly paying attention to 393nm, 430nm, and 656nm. My understanding of an SCT is that it's not very good at 393nm. I don't know much about a solar newtonian (decoated?). I'm very familiar with refractors for solar. Some of these designs would use a single ERF that passes the appropriate frequencies. And some designs could use several different ERFs for different applications (such as a truss Refractor, to allow internal ERFs specific to the frequencies that can be interchanged).

I'm also looking at the relative cost of each system, excluding the actual narrowband filters and associated blocking filters (if applicable). Mainly just looking at the telescope design and the thermal handling (in the form of the ERF for it).

Of course there is also the question of "what is high resolution?" with respect to aperture and scale for solar imaging. I think we can all agree on large apertures, however, I'm curious what the smallest aperture of each instrument design would still provide what one would consider high resolution? I think we all have an understanding that there are practical limits with respect to our seeing in various places and that there's a point where you'll not benefit from a large scale system, and of course, how do you find that limits without already having such a system?

For simplicity, let's have a thought experiment around the 8 inch aperture. I think we can agree this is fairly high resolution for solar application. It's a relatively common and affordable aperture in all three telescope designs. And it's overall dimensions and weight can be handled on fair mounting equipment. And there are different means to apply energy rejection, both external full aperture, external partial aperture and internal filtration approaches.

Thanks for your time! :bow2

Very best,

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by marktownley » Sat Sep 22, 2018 9:41 am

For me the Baader Tri-band SCT offers great value for money and in a range of sizes to suit local seeing.

http://astrograph.net/epages/www_astrog ... Telescopes
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Re: What do you think is the most versatile high resolution solar telescope design?

Post by george9 » Sat Sep 22, 2018 12:27 pm

I notice that Baader does not use the Edge version of the Celestron. Whereas AiryLabs does. And of course, with a front-mounted ERF, you can do what you want. Anyone notice a difference in performance? Especially at 393nm?

George

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by christian viladrich » Sat Sep 22, 2018 6:06 pm

My 10 cents :

With a 8-inch SC :
- with the appropriated filter : photosphere is OK from about 450 nm and beyond,
- with the appropriated filter : chromosphere is OK in Ha.
In a nutshel, a C8 (EdheHD or not) is useless for K-line ou Ca K imaging because it is not diffraction limited below about 450 nm.

With a 8-inch Cassegrain, Dall-Kirkham or Newton :
- with the appropriated filter : photosphere is OK at whatever wavelengths (depending on the surface accurary of the optics),
- with the appropriated filter : chromosphere is OK in Ca K and Ha.
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Re: What do you think is the most versatile high resolution solar telescope design?

Post by TheSkyBurner » Sun Sep 23, 2018 4:40 am

all that matters is strehl ratio. my 2 cents.

This is what makes or breaks a solar scope.

The tec140 is .99 strehl at 546nm, so it will produce flawless convection cell images, with astro solar film.
(8,204.02 United States Dollars, complete scope)

the istar 150h-alpha is .98 strehl at 656.3nm, so it will produce flawless h-alpha images; with a full size h-alpha d-erf.
($1,299.00 objective only, no ota)

and right now, currently ZERO lenses are manufactured to produce .98 strehl at 393nm. Not a single one.
(the design exists but nobody is going to make it for any reasonable cost, $5000 just for the 150mm objective; unmounted, no ota.)

.


you will always be sacrificing one wavelength for another. Now as mark has stated, dollar ratio for mm of objective is the purpose built baader planetarium triband SCT. The strehl ratio is only par however, not spectacular at all.
(good luck getting it shipped to the united states)

the other answer is a true super-apo , corrected for all wavelengths including uv and infrared. (still limited by strehl) ($15,000+)

While perfection is possible if you throw a life saving at it, There is however a great alternative.

The long 150mm x 2250mm F/15 refractor. This is .92 strehl all around, 656, 540, 430, 393. The flaw here, is you need an incredible mount because the scope is 8 feet long.

The triband erf, cost as much as the scope also, so you are looking at 4000$ + another $5000 for the mount.

I have this f/15 scope, but never could afford a way to mount it, so it still sits brand new in its original box

I apologize for suggesting the 150mm objectives. The longer the focal length the better correction any scope will have however

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by Valery » Sun Sep 23, 2018 6:46 pm

ARIES' solution for SCTs at 430nm and 393nm.

download/file.php?id=34233
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by TheSkyBurner » Sun Sep 23, 2018 11:10 pm

Valery wrote:
Sun Sep 23, 2018 6:46 pm
ARIES' solution for SCTs at 430nm and 393nm.

download/file.php?id=34233
Valery that picture is amazingly 3d. You should nasa apod that.

Its like a massive wilson effect! :bow

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by MalVeauX » Fri Sep 28, 2018 1:48 pm

I've been looking at different designs and ERF options to see what's versatile and does the job, but also with a budget in mind, and relative ease of mounting (as to not require a mount far more expensive just to carry the thing of course).

I think a large refractor is very versatile, and easier to install energy rejection filters since they can go internal a little behind the front objective. 8 inch lenses are around $2k. The only issue is of course the tremendous moment arm of a long large heavy refractor (even at F6.5~F7). This sort of instrument would require a lot of mount just from the moment arm perspective, even a "shorty" 8 inch refractor is long and heavy (that's also assuming a truss refrator design with modular ERF options internally).

I've been trying to learn more about solar reflectors, with dealuminized mirrors to act as herschel wedges but with monstrous aperture. Also interesting to consider and obvious versatile from the standpoint of being a fairly inexpensive means to get a big aperture that is full spectrum and already has a lot of thermal load reduction, so it could potentially be fairly cost effective, from the aperture stand point, for what it is. The problem becomes the size and weight putting a lot of stress on a mount, with a huge moment arm and being a wind catcher. Then again, a truss design might help there perhaps. I'm still looking up information on this as I don't know enough about how the dealuminizing process is done and whether it's anything more than a white light instrument, or if it at all can be used for other frequencies like HA, etc.

The SCT is a very attractive design from the standpoint of being very compact, light weight, and fairly inexpensive to get too. The ERF is where the cost and consideration changes things big time if wanting full aperture. I guess I'm still ignorant to the difference of a SCT mirror and a reflector mirror with respect to 393nm and resolution and I need to research a little more on this subject. It seems like this design would be very vesatile and cost effective and really attractive from the mounting standpoint (being small and compact and light weight, it could comfortably ride lesser mounts and even potentially have a little 60mm full disc scope with it for a very nice pair to cover wide FOV and narrow FOV). But I'm still curious about not being diffraction limited for calcium.

Curious indeed!

Very best,

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by christian viladrich » Fri Sep 28, 2018 5:37 pm

Hello Marty,

The field of use of an uncoated mirror is the same as with an Hershel wedge. This is "white light" observing and imaging.

The main benefit of an uncoated mirror is the level of transmission compared to an Astrosolar d3.8 full aperture filter. This makes possible the use narrow band filters from about 1 nm FWHM (and larger) with very short exposure times.
The range of filters I use with my 300 mm Newtonian teelscope is : 396 nm FWHM 8 nm, 430 nm FWHM 1.9 nm, 500 nm FWHm 12 nm, 656 nm FWHM 12 nm.

There is no enough light to use filters narrower than about 1 nm FWHM.

Back to the SC... They suffer from spherochromatism (because of the Schmidt plate). This means that the spherical aberration depends on the wavelength. There are designed for red or green light. They are no longer diffraction limited below about 450 nm.
Here is the Strelh ratio for various Celestron SC. The optics is no longer diffraction limited when the Strelh ratio goes below 0.8 :
Image

So the SC is definelty not for Ca K observation, except if associated with corrector for spherical aberration designed for Ca K.

Hope this helps.

Best regards
Christian Viladrich
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Co-author of "Astronomie Solaire"
http://www.astronomiesolaire.com/

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Re: What do you think is the most versatile high resolution solar telescope design?

Post by christian viladrich » Fri Sep 28, 2018 5:53 pm

BTW, more information on the SC optical performances for HR imaging :
http://astrosurf.com/viladrich/astro/in ... sis-SC.htm

And analysis of telescope designs :
http://astrosurf.com/viladrich/astro/in ... alysis.htm
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Co-author of "Astronomie Solaire"
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Re: What do you think is the most versatile high resolution solar telescope design?

Post by MalVeauX » Fri Sep 28, 2018 6:25 pm

Thank you Chrisitian, extremely helpful! :bow :bow

Very best,

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