Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

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ammonthenephite
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Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by ammonthenephite » Mon Feb 15, 2021 11:49 pm

Hello, quick question for the community. I'm in a locaiton with routine excellent seeing (on maui with Haleakala about 40min away), and wanted to add a high resolution option to my solar imaging to complement the lunt 100. The two main options are either a c8 or c11, with accompanying aries DERF. I all ready own a c11 edge, and do not own a c8 edge (would want the edge for addition of fans for internal current stabilization). So, I'd either be buying a c8 edge + DERF, or simply a derf for the c11, which last I checked was about twice the price of the c8 derf. So, the two options in the end are not too dissimilar in total price, since the rear h-alpha etalon will be the same for both (likely a solar spectrum observer 25mm, unless people have suggestions for similar quality options there?)

So my main 2 questions, for those that have imaged or viewed h-alpha through both a c8 AND and c11, are 1) how would you compare the fine detail difference between the two? Was it "omg the difference it night and day!", "ya, there is a noticeable difference", or simply more of "ya, if I look hard I can tell a difference but its miminal..."? The dawes/raleigh limit between the 2 in resolving ability is in theory only about 0.2 arcseconds, but I'm unsure of how this would play out in real life. Meteoblue has the top of Haleakala routinely at 0.2-0.5, so in theory there could be a difference, but not sure if other factors (outside of things like collimation and the like) reduce the real world views between the 2 a lot, or if there is a noticeable difference you see bewteen both?

And 2) are there other things bewteen the c8 and c11 you noticed that would, in your mind, make one much (or at least somewhat) more preferable between the two, such as backfocus (when using reducers or barlows, etc), size and weight of each for setup/takedown/transport, etc?

Basically, all things considered, if you had great seeing conditions on a routine basis, but you had to drive 40ish minutes to get to them (so you setup had to be broken down and set up each use), which would you prefer to have? Since I'm unsure of the realworld difference in detail between a c8 and c11 with good skies, its the last remaining 'unknown' in the equation, so I look to those here that have experience with both as to whether or not the detail differences between the 2 are worth the weight/inconvenience penalty!

Thank you in advance.


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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by marktownley » Tue Feb 16, 2021 8:00 am

Hi There.

I don't have direct experience of the comparison between the 2 scopes, but what I do know is if you have access to such a location and you are able to exploit it then do so.

How 'accurate' is the meteoblue seeing figure? Are you taking it for granted as correct? I appreciate it is Haleakula, but it may be worth taking a SSM up there and surveying the site for local variations in the figure.

My other thought with the larger scope is how 'physically able' are you for lugging it around at high altitude? Also do you have a sufficient mount for the larger scope The lack of oxygen when I was at the summit of Mauna Kea was interesting to say the least.

I'm just playing devils advocate here, but I think i'd be getting the DERF for the C11, if conditions sometimes don't support it then you can always stop down. The other thing I would be looking at is CaK, that high up in the atmosphere and with that seeing would be very interesting - a 'cheap' solar newton would give awesome results.

Make sure you take some pics the next time you are up there to show us all!

Mark


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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by christian viladrich » Tue Feb 16, 2021 12:42 pm

Hello,
Here is an answer with three images taken on the same day, similar resolution, SolarSpectrum RG 0.3A and C8 EdgeHD or C11-Edge-HD :

C8 EdgeHD at F27, peak seeing = 0.68 arcsec :

http://astrosurf.com/viladrich/astro/so ... 03A-C8.jpg

C8 EdgeHD at F35, peak seeing = 0.61 arcsec, slightly better resolution due to increased sampling :

http://astrosurf.com/viladrich/astro/so ... C8-F35.jpg

C11 EdgeHD at F27, peak seeing = 0.41 arcsec, much better resolution due to the large aperture :

http://astrosurf.com/viladrich/astro/so ... 3A-F27.jpg

You can compare these images more easily if you put them side by side (for example with Photoshop).

So yes, if you have adequate seeing, the larger aperture will provide better resolution.

Still, there are a few caveats :
- Mark's remarks are quite pertinent,
- in additional, keeping the collimation straight in a C11 is very challenging even when you observe at home. Keeping collimation straight if you have to drive your car 40 min is simply a dream. This is not possible. You will lose all the benefit of the larger aperture by having bad collimation.
- On my side, I collimate my 300 mm Newtonian on the solar granulation. This is feasible only in white light and if you have an excellent observing site, and ... some experience.
At the end of the day, the main question is : can you set up your SC at night, collimate it on stars, and let it there for the following morning ?

Otherwise, a 230 mm refractor corrected for Ha is probably the largest "trouble free" instrument (very stable collimation).

Hope this helps.


Christian Viladrich
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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by ammonthenephite » Tue Feb 16, 2021 9:06 pm

Wow, great information ya all, truly appreciated! Excellent questions Mark. I'm still young enough that hefting her up there is still very doable, in fact I'll be up there regulary with her doing deep space imaging and planetary all ready. So on the ideal days I'll get up there at 0100-0200, do my night stuff, let the sun rise then grab early morning solar with the scope collimated. Used to high altitude as well, coming from Colorado, so I know to pace myself and recognize the signs of clumsyiess or light headedness that can happen should one over exert.

And excellent comparison images, Christian! While its not super night and day, there is a noticeable difference when zooming in there, which given the opportunity of where I'm at, I'm inclined to agree with Mark that I should take advantage of such seeing, as this may be the only time in my life where it is readily available.

Also good question on the actual seeing up there. I'm going to head up today or tomorrow with the lunt 100 (if I can remember in what boxes I packed all the ancillary gear, lol) to do a real world test. But I have been comparing Mauna Kea's real world measurements (found here) http://mkwc.ifa.hawaii.edu/forecast/mko/trends/ with meteoblue's predictions (found here) https://www.meteoblue.com/en/weather/ou ... ca_5850911, and they seem to be, at worst, within 0.5 arcesonds, and often within 0.2-0.3. So I'm not expecting exactly what meteoblue predicts, as nice as that would be!

So, I guess then just 2 follow up questions - Does Valery (I think he is the one that does airlyabs?) have a website for ordering his derfs?

And Christian, out of curiosity, what is the widest FOV you are able to get with your c8 and c11? Curious as to how much one can backout/reduce with both for maximum disc coverage, for when solar activity really picks up and very large structures begin to appear? For 1/4-full disc images I'd use my lunt 100, but wondering just how wide field one can get with a c8/c11 while still being enough on band to get useable data?

Seriously, thank you both for such helpful information, I truly appreciate it!


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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by christian viladrich » Wed Feb 17, 2021 9:10 am

Hello,
Regarding seeing condition, it is worth checking whether real time seeing data from the observatories on top of Mauna Kea are in open access.
Here are the data from CHFT :
http://mkwc.ifa.hawaii.edu/current/seeing/index.cgi
For some reasons, recent data is not available.

Some statistics :
Image
and also :
http://mkwc.ifa.hawaii.edu/current/seei ... s/catalog/
This is one of the best site in the world. Of course this is only night time.

Where are you planning to set your telescope exactly ?


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http://planetary-astronomy.com/
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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by Valery » Wed Feb 17, 2021 12:17 pm

ammonthenephite,

PM sent.


"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: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by christian viladrich » Wed Feb 17, 2021 3:04 pm

ammonthenephite wrote:
Tue Feb 16, 2021 9:06 pm
And Christian, out of curiosity, what is the widest FOV you are able to get with your c8 and c11?
There are several limits on the FOV :
- the free aperture of the Ha filter. Check out the price of a 42 mm Solar Spectrum ;-)
- degradation of image quality as we move away from the optical axis, which depends on :

(1) SC optical type. Indeed,as you can see here, the diffraction limited flat field of the EdgeHD is much larger than the "classic" SC :
http://astrosurf.com/viladrich/astro/in ... -Field.jpg
(2) correction of the field by the telecentric lens :
AiryLab telecentric lens (Fred Jabet is the owner) are optimized for the SC EdgeHD. Non optimized telecentric would give smaller diffraction limited flat field.

If you are looking for hhe best possible HR imaging with a SC, it is more relevant to use an EdgeHD with the associated optimized telecentric lens.


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

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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by ammonthenephite » Fri Feb 19, 2021 1:27 am

Well, got up to Haleakala, but unfortunately it was within a day of a big system moving in, so seeing wasn't great. Unfortunately I have no way of quantifiying what the seeing really was execept for 'about an average day of what I had while in Colorado, not as good as the best days in Colorado'. Should clear out with more stable conditions by monday, so I'll get up a couple more times for 'sample seeing'. Even though meteoblue was saying there should have been 0.4 arcsecond seeing, it didn't feel like it, though there were some very brief moments of decent to good seeing. If I see the same thing even after the system has moved out, I may go for the c8, but if I can get at least one good day in where I can really max out the lunt 100 and want more, then I think the c11 will be worth it.

Here is the only test image to yield detail, hastily processed just to see what detail was present (and my main processing computer isn't unpacked yet, be a few more days before I can get that set up). This is the Lunt 100 with 2.5x televue and ROI of 1920x1080 on the asi178mm, so as high as I normally took the lunt while in Colorado. Contrast is less as well prior to the minimal processing, not sure if that's just down to being a bit off band or if tropical air at 10k feet is just hazier than Colorado desert air at 5k feet. Detail is there, just not tac sharp like I'd often get in Colorado. Pushing the sharpening/deconvolution any more would start to create a host of artifacts.

Image

So, not terrible, just not enough per this "sample of 1" to merit a c11. But, that's just one pre-test outing right before bad weather moving in. Will be interesting to see what is viewable come monday and tuesday when the sun returns and weather calms down a bit.

And if the sun is listening, a sunspot would be great right now so as to have something with known high contrast and sharp edges for testing purposes...

Thanks again to everyone for the great info and insights, I'll keep ya all posted!


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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by DavidP » Fri Feb 19, 2021 1:56 am

Hey
It sounds like a Airylab Solar Scintillation Monitor would be a good investment for you to get some real data on seeing at your site. Setting the sensor next to your aperture will tell you exactly what you have. If it were me, I would use one for as many sessions as possible with your present set-up before making a decision. It would be a shame to invest in a c11 set-up when an 8 might serve you as well or better... or vice versa.



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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by ammonthenephite » Fri Feb 19, 2021 2:00 am

Oh wow, I didn't even know such a thing existed! Will look into that asap, that would be great to have hard numbers at least.

Edit - rats, looks like they are 14-28 days out, plus another week to reach me. I'll see how I do with a few imaging sessions, visually assessing the final detail in some more stacked images, and see if there is an obvious answer to what detail I can hope to achieve here.


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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by marktownley » Fri Feb 19, 2021 7:58 am

ammonthenephite wrote:
Fri Feb 19, 2021 1:27 am

Here is the only test image to yield detail, hastily processed just to see what detail was present (and my main processing computer isn't unpacked yet, be a few more days before I can get that set up). This is the Lunt 100 with 2.5x televue and ROI of 1920x1080 on the asi178mm, so as high as I normally took the lunt while in Colorado. Contrast is less as well prior to the minimal processing, not sure if that's just down to being a bit off band or if tropical air at 10k feet is just hazier than Colorado desert air at 5k feet. Detail is there, just not tac sharp like I'd often get in Colorado. Pushing the sharpening/deconvolution any more would start to create a host of artifacts.

Image
You do realise you are hugely oversampling with this camera and your setup? The 2.4um pixels of the 178 are more suited to prime focus with the LS100 than using a 2.5x powermate. This oversampling would give a softness to the image. I'd recommend if you are going to shell out a wadge of $$$ on a DERF for the C11, decide what etalon system you are going to use and then select a camera whose pixel pitch matches the focal ratio, probably an IMX174 chip I would suggest.


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Re: Realworld difference between C8 and C11 h-alpha levels of detail with excellent seeing?

Post by ammonthenephite » Fri Feb 19, 2021 9:30 pm

Ya, my current system does heavily oversample at this level of magnification! As I've eased into this hobby, I started with a 'jack of all trades, master of none' kind of set up. While I oversample hugely here, those small pixels come into play when I put on the 0.5 reducer and do full disc imaging with the same scope. I will be eventually getting a second camera for the high res stuff, but have no idea what to get at this point. My current 178mm suffers from fixed pattern sensor noise (I did a post a while back on it here: https://www.cloudynights.com/topic/7004 ... a-imaging/ )which limits my ability to sharpen the small details (most noticeable when doing full disc imaging ironically), and from what I've read a lot of people have it even worse with the 174 and 183 (I think I have those numbers right?) sensors as well. Seems to be an issue with some of the sony exmor sensors. Not sure what alternatives there are, as its an area I haven't heavily researched yet.

But yes, you are correct, I do heavily oversample at this magnification. Though when living in Colorado I had quite a few days where I could still get sharp and well defined images at this magnification. I'll hopefully get some better sample images this monday after the weather stabilizes a bit and I can get up there earlier in the morning for the better seeing.

Again though, thank you so much for the input and help you've given me, both on this and in many past threads. I hugely appreciate the massive experience and willing to share that you and so many here have! Its a great community here, and I wouldn't be getting half the enjoyment I get from this hobby were it not for all ya all:)


Lunt LS100THA singel stack on Skyview pro mount
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