AR2822 WL (High Res), CaK, HA | May 14th 2021

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AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

Hi all,

Stormed and rained so far this week, but this morning was clear, lower temps and pretty ok seeing conditions between gusts. AR2822 is still looking good with a nice penumbra around the spot in the photosphere and lots of interesting activity in the chromosphere and popping off little flares.

High Res Photosphere:


Image

Image


Moderate Res Chromosphere:

(Doh, mislabeled the wavelength.... sigh, lol, its 3934A)


Image

Image

Image

Image

Image

Image


Seeing Conditions:

seeing05142021.png
seeing05142021.png (385.11 KiB) Viewed 647 times

Equipment:


120mm F10 Refractor (C6R masked)
2" Internal sub-aperture D-ERF (Baader Blue CCD-IR Block Filter) + Lunt CaK B1200 + 290MM sensor (CaK)
2" Internal sub-aperture D-ERF (Baader Red CCD-IR Block Filter) + PST Etalon + 2x 1.7A Blocking Filters + 290MM sensor (HA)

200mm F10 SCT + Full Aperture D-ERF
Baader Red CCD-IR Block Filter + Baader ND 3.0 Filter + 290MM sensor (Photosphere)

solarsetup_05142021.jpg
solarsetup_05142021.jpg (73.26 KiB) Viewed 647 times

Very best,


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MAURITS »

Beautiful and clean images Marty.


Regards,
Maurits

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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by DeepSolar64 »

These are very nice Marty. All of them. The high resolution photosphere images are my favorites. Very nice granulation!!

James


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by p_zetner »

Great series, Marty.
I agree that the photosphere shots really pop.
Cheers.
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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by Ylem »

Nice details Marty!
Very nice πŸ‘


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by EGRAY_OBSERVATORY »

Beautiful set of images and presentation Marty.

Thanks vm for sharing
Terry


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

Excellent photos Marty as usually. I love your WL resolution.

Also a lot of food for thought for me, since you are providing the SSM measurements... (many thanks for sharing them).

Please have a look at the SSM I had the first day I had up in the mountain at 1800 m altitude. I think it is similar to the one you presented if not better.
Seeing at 1800 m altitude.jpg
Seeing at 1800 m altitude.jpg (322.45 KiB) Viewed 591 times
The blue part corresponds to 30 second captures.

However, my results from that session are really horrible (below). Visually the sun surface was similar.
Sun WL_19_34_36_IR_pass_685_nm.jpg
Sun WL_19_34_36_IR_pass_685_nm.jpg (981.47 KiB) Viewed 591 times
The difference with your photo is huge. Day and night... What could be so wrong with my C8??? I suppose the difference could not be due to the Baader Astrosolar that I use, instead of your DERF. I have checked the collimation several times and it was fine (although not in the mountains). I will check it again now back home. However, there were some few days with almost similar conditions at home where the collimation was certainly perfect, but the results were similar... What goes so wrong with my C8 Hi-Res WL? What the age of the scope (30 years) could have provoked that I do not see at first sight? It is still a mystery for me...

Any idea is welcome.

Bets wishes,
Alexandros


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

H-Alpha wrote: ↑Sat May 15, 2021 12:27 am Excellent photos Marty as usually. I love your WL resolution.

Also a lot of food for thought for me, since you are providing the SSM measurements... (many thanks for sharing them).

Please have a look at the SSM I had the first day I had up in the mountain at 1800 m altitude. I think it is similar to the one you presented if not better.

Seeing at 1800 m altitude.jpg

The blue part corresponds to 30 second captures.

However, my results from that session are really horrible (below). Visually the sun surface was similar.

The difference with your photo is huge. Day and night... What could be so wrong with my C8??? I suppose the difference could not be due to the Baader Astrosolar that I use, instead of your DERF. I have checked the collimation several times and it was fine (although not in the mountains). I will check it again now back home. However, there were some few days with almost similar conditions at home where the collimation was certainly perfect, but the results were similar... What goes so wrong with my C8 Hi-Res WL? What the age of the scope (30 years) could have provoked that I do not see at first sight? It is still a mystery for me...

Any idea is welcome.

Bets wishes,
Alexandros
Hi,

Well, a couple of things are at play. The seeing measurements are not absolute. They only measure up to a point so there can be things even farther up that disrupt seeing that the SSM cannot see. If you look at the 1 minute average, you may have good seeing averaged, but what matters is the peaks that are being achieved when it comes to attempting high res imaging as that's where lucky imaging comes in.

My peaks were around 0.7 arc-seconds with a much worse 1 minute average, however, those momentary peaks were good enough to allow me to get critical focus.

And this is the key part, when seeing is poor and variable, getting focus with a high res system is difficult because how do you know you're even in focus? With only convection cells to focus on, focus is very hard to obtain due to variability of seeing and the low contrast of the surface. To help with this, other than having good seeing, I use the screen overlay function in FireCapture that allows you to adjust gamma / contrast and brightness, real time, but without it being embedded into the recording so you can see the features better on a screen and get focus and also see the seeing conditions and know when to capture without embedding the gamma, contrast, brightness, etc, into it and ruining your recording. It helps a lot.

Local seeing conditions are also important (not just atmospheric seeing), so the ground itself, surrounding material, etc, matters. If anything is allowing heat to rise into your OTA, it will ruin seeing. The C8 tube is very vulnerable to rising heat plumes/currents (just put your hand under it and watch an airy disc on a star, it will go fuzzy right away from your body heat alone!). I put reflectix material around my OTA as a barrier to any rising heat sources (such as the metal on the mount itself soaking up heat from expoure). I try to cover my mount too with this material. It's just a reflective barrier to avoid anything become a heat sink and letting heat rise. Florida is already hot, and the sun is blistering hot too, so just preventing any potential source of local heating is ideal. My scope is over 6 feet off the ground too (2 meters) to avoid ground heat influence.

And of course, lucky imaging, faster FPS is always better for getting a chance to get a lot of good frames. I'm imaging at 170 FPS so when I do a sequence run, I end up with a lot of frames of course, but the point is the speed, so that even a half of a second of good seeing allows me about 80 frames during that time and that's plenty to get an image from. So all I need is half a second of good seeing, or even a quarter of a second of good seeing, and I can make an image like this. Faster speed would be even better.

Baader Solar FIlm is perfect for this. I use it too, ND3.8 Baader Solar Film on my 8 inch scopes. It does the same job as DERF in white light photosphere imaging. Transmission is high. I absolutely did not need to use my DERF for this at all, it was pointless to use it honestly since my solar film could have done it too. There's no difference between these two for photosphere imaging in reality. Also my particular DERF passes a lot of heat, lots, so I complete the blocking with a 2nd filter in the imaging train. Solar film on the other hand does not pass all that heat, and is likely more thermally stable on my larger aperture scope. My DERF is only actually needed for narrowband chromosphere imaging like HA at the end of the day on a mirror based optic. For everything else, I use internal sub-aperture DERF on refractors and have no need for a full aperture DERF on them and my results seem fine and have been doing it that way for years with zero broken filters or issues and my scopes are black colored paint in Florida heat.

The age of your scope shouldn't matter much, the coatings are important at night, but in the day time, transmission is so high that you could probably image with it even if the coatings had flaked off. More important is mirror shift (due to primary focusing), collimation (but rough collimation still works for this), temperature deltas and local heat sources under the OTA.

If I had to guess, I'm guessing your image simply wasn't at critical focus and it was due to seeing variability and not being able to get critical focus. Without knowing your imaging train, the focuser matters a lot with SCT as the primary focuser moves the mirror and shifts it. This is really bad for imaging. I suggest if you have no already, put a crayford or similar focuser on the visual back. Move the primary mirror into rough focus, but do fine focus with the 2nd focuser on visual back that does NOT move the primary mirror to avoid any mirror shift.

High res imaging is not easy, but it's 99.99% seeing related even with simple hardware since seeing even effects if you were in focus in the first place or not.

Practice and seeing is what it takes! You'll nail it.

Very best,


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by marktownley »

Great shots Marty! Glad the seeing was playing ball for you!


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

Thanks so much Marty once more for the detailed answer!

I am already doing EVERYTHING that you wrote following your tutorial Youtube and previous precious advice you have given me (including 180 fps, focuser on the visual back and gamma focusing on a sunspot, removing gamma for capture)! Everything (literally) except one thing...

I have never covered the tube and tripod to protect them from heating (we were not yet in summer, but this could have made things even worst due to temperature differences?) and the tube is at about 1.5 m from the ground (not 2 m). The ground at home cannot be as I would have wished it, since this is a balcony, but it was just earth (unfortunately there was no proper grass place) up in the mountains. I will try to improve this point as well, hoping to see better results in the future.

I wish I lived closer to an experienced solar photographer..., but from another point of you, after struggling to achieve something, the pleasure is even higher when we finally succeed following kind and precise advice! ;-)

All the best,
Alexandros


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by marktownley »

H-Alpha wrote: ↑Sat May 15, 2021 12:27 am Excellent photos Marty as usually. I love your WL resolution.

Also a lot of food for thought for me, since you are providing the SSM measurements... (many thanks for sharing them).

Please have a look at the SSM I had the first day I had up in the mountain at 1800 m altitude. I think it is similar to the one you presented if not better.

Seeing at 1800 m altitude.jpg

The blue part corresponds to 30 second captures.

However, my results from that session are really horrible (below). Visually the sun surface was similar.

Sun WL_19_34_36_IR_pass_685_nm.jpg

The difference with your photo is huge. Day and night... What could be so wrong with my C8??? I suppose the difference could not be due to the Baader Astrosolar that I use, instead of your DERF. I have checked the collimation several times and it was fine (although not in the mountains). I will check it again now back home. However, there were some few days with almost similar conditions at home where the collimation was certainly perfect, but the results were similar... What goes so wrong with my C8 Hi-Res WL? What the age of the scope (30 years) could have provoked that I do not see at first sight? It is still a mystery for me...

Any idea is welcome.

Bets wishes,
Alexandros
Have you a different camera you can use? Maybe the stacking software is honing in on the fixed pattern noise of the chip rather than the actual signal?


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

H-Alpha wrote: ↑Sat May 15, 2021 1:49 pm Thanks so much Marty once more for the detailed answer!

I am already doing EVERYTHING that you wrote following your tutorial Youtube and previous precious advice you have given me (including 180 fps, focuser on the visual back and gamma focusing on a sunspot, removing gamma for capture)! Everything (literally) except one thing...

I have never covered the tube and tripod to protect them from heating (we were not yet in summer, but this could have made things even worst due to temperature differences?) and the tube is at about 1.5 m from the ground (not 2 m). The ground at home cannot be as I would have wished it, since this is a balcony, but it was just earth (unfortunately there was no proper grass place) up in the mountains. I will try to improve this point as well, hoping to see better results in the future.

I wish I lived closer to an experienced solar photographer..., but from another point of you, after struggling to achieve something, the pleasure is even higher when we finally succeed following kind and precise advice! ;-)

All the best,
Alexandros
It may take a few more tries, but I suspect it was out of focus with a local or high atmospheric seeing conditions effecting things so that you couldn't see critical focus. Convection cells are quite hard to see in high contrast and focus with rapidly changing seeing and blur, and being focused or unfocused is a tiny smidge on a focuser, so its hard. I miss it too sometimes still when the seeing isn't supportive of the image scale and aperture. If I can't get focus and feel confident about it (ie, I can see the individual convection cells as boxes briefly when I'm focused with contrast overlay to make it easier) then I just don't image with it and drop down to smaller aperture instrument.

About 1 meter is sufficient from the ground (Christian measured it nicely for us all). I go higher due to my observatory walls and low elevation angle imaging that I do in the morning.

Gravel, rocks and sand can be a heat sink. Often a tarp is used as another barrier on the ground. Some people spray the ground with water around them (obviously not an option up in the mountains).

I don't have a good way to measure it accurately, but as you can see in my setup images, I cover all surfaces I can with a reflectix barrier to keep my metal mount and pier and other stuff from direct sun exposure which heats up fast. My OTAs and mount surfaces are so hot to touch that it burns my hand when just sitting in the sun like this even for just 30 minutes in the morning here in Florida. When my scopes are pointed at the sun, its no problem, because the walls do not receive direct exposure. But you can see even on my refractor I will mask with the same material to avoid the front of the scope also becoming a heat point from the material itself being black plastic and getting hot. I actually need to wrap my refractor too, just haven't, lazy, since I can usually image no problem with it at its smaller image scale. But doing this has helped me a lot, I found, with all my setups simply because the metal of the mount was releasing heat right up into the OTA and it was obvious to on the screen like a fire was under there. Once I wrapped it up and put barriers, that stopped. The mount, pier and pier plates themselves were getting hot from direct sun and the heat was rising up into my imaging train.

Very best,


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by Stardust5858 »

Lovely Marty, thanks for sharing.


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

marktownley wrote: ↑Sat May 15, 2021 1:59 pm
Have you a different camera you can use? Maybe the stacking software is honing in on the fixed pattern noise of the chip rather than the actual signal?

Thanks a lot Mark!
I did not know it can happen... Nevertheless I have observed very often if not always vertical lines on the stacked images of the ASI290 and I wondered if this was normal or not... I wanted to send an example here to ask if anyone had the same experience, so you give me now the opportunity.

I have no alternative camera apart a Canon EOS5D rs, which is something completely different. I may have to try to buy the 1600 earlier than planed...

Here is what I get as vertical lines when I zoom in on the stacked photos by AutoStakkert.
Vertical Line noise in stacked ASI290 images.jpg
Vertical Line noise in stacked ASI290 images.jpg (346.73 KiB) Viewed 517 times
I tried a relevant option in AutoStakkert regarding vertical line noise to see if I could fix that, but it returns completely white images...

Are these lines normal or something is wrong with my ASI290? And HAVE YOU ANY IDEA HOW TO TEST THE CAMERA?

All the best,
Alexandros


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

Hi,

Note that your example is a 400% view. I don't see grid pattern in your image either, just pixels from 400% view.

I use a 290MM and see no grid.

The grid Mark referred to is most prominently noted on the IMX178 and IMX183 sensors and its due to the matrix, even on a mono sensor, having some pixels show brighter, as the red is brighter, significantly than green and blue. Again, despite no bayer matrix, this pattern exists on the mono IMX178 and IMX183 still and has been shown a few times. It's Sony's error. So the brightness differences on the pixels results in a grid pattern (square blocks) that is similar to the bayer matrix and it gets stacked in since its constant.

Very best,


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by marktownley »

MalVeauX wrote: ↑Sat May 15, 2021 6:59 pm Note that your example is a 400% view. I don't see grid pattern in your image either, just pixels from 400% view.
You see, Marty was paying attention, and I was not. Missed the 400% view screen. It's either seeing, tube currents or collimation that are the issue.

I'm sorry H-alpha, but unless your conditions are near perfect I honestly think you're wasting your time with a SCT.


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by robert »

Getting a short exposure time, ie less than 10ms nearer 1ms helps in my experience of granulation imaging, even increasing gain to achieve this, and Baader Continuum filter is helpful

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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

Thank you Mark, Marty and Robert for your helpful comments.

Mark, now with my Lunt130MT that just arrived, I won't try the C8 for solar anymore, unless I dedicate some days up in the mountains again. Before I had nothing but the C8. Now, "discovering" the Lunt130 Sun, will keep me happy and busy for many months/years to come I hope. :-)

Best wishes,
Alexandros


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

robert wrote: ↑Sat May 15, 2021 7:21 pm Getting a short exposure time, ie less than 10ms nearer 1ms helps in my experience of granulation imaging, even increasing gain to achieve this, and Baader Continuum filter is helpful

Robert
Hi,

I would argue that a Baader Continuum filter is not always helpful, especially with large aperture instruments and average seeing conditions. The optics are ideal for green wavelength, but red is not far from this either, so the results of either wavelength on the optic are not what is going to make a difference, but rather the seeing. The contrast difference is just angular resolution, but only secondary to atmospheric seeing allowing that resolution to even be realized. 540nm requires better seeing conditions than a 610~656nm red wavelength does. So if you are trying to image with a 200mm aperture and your seeing is 0.7~1.0 arc-seconds, you might be able to pull it off with a red wavelength and get the near max resolution of it. But trying to do the same with 540nm requires nearly 20% better seeing conditions to benefit the higher angular resolution, and it would require a finer image scale (critically sampling the shorter wavelength) along with the better seeing conditions. So I would argue, if you're trying to image with 200mm, and you're not successful due to seeing limitations, red or long wavelength is where you should start. Switching to green wavelength like Continuum will make it more difficult in the same conditions due to needing even better seeing conditions. Continuum or shorter (down to near UV even) requires 0.6 arc-seconds and less, down closer to 0.3~0.4 arc-seconds to attempt near UV, and around 0.5~0.6 arc-seconds for Continuum (540nm) with a 200mm aperture. So unless you have that kind of seeing, use red.

Very best,


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

H-Alpha wrote: ↑Sat May 15, 2021 7:31 pm Thank you Mark, Marty and Robert for your helpful comments.

Mark, now with my Lunt130MT that just arrived, I won't try the C8 for solar anymore, unless I dedicate some days up in the mountains again. Before I had nothing but the C8. Now, "discovering" the Lunt130 Sun, will keep me happy and busy for many months/years to come I hope. :-)

Best wishes,
Alexandros
130mm aperture is a lot of aperture on solar in reality. You'll get more usable data each session with red wavelength in the 130mm range. You can top it off in the 1.1~1.2 arc-second range.

Since its modular you can of course image the photosphere with it too and it will be good for that as well in lesser seeing conditions.

Another option if you're interested in photosphere imaging is to look at a 6" optic like a 6" F6 newtonian or similar, they're inexpensive and good for this with solar film allowing a dedicated instrument for a tiny cost. Or a C6 SCT even. C8's are nice, but for solar, you need really great seeing conditions to resolve things with 200mm aperture.

Very best,


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by DeepSolar64 »

H-Alpha wrote: ↑Sat May 15, 2021 6:48 pm
marktownley wrote: ↑Sat May 15, 2021 1:59 pm
Have you a different camera you can use? Maybe the stacking software is honing in on the fixed pattern noise of the chip rather than the actual signal?

Thanks a lot Mark!
I did not know it can happen... Nevertheless I have observed very often if not always vertical lines on the stacked images of the ASI290 and I wondered if this was normal or not... I wanted to send an example here to ask if anyone had the same experience, so you give me now the opportunity.

I have no alternative camera apart a Canon EOS5D rs, which is something completely different. I may have to try to buy the 1600 earlier than planed...

Here is what I get as vertical lines when I zoom in on the stacked photos by AutoStakkert.

Vertical Line noise in stacked ASI290 images.jpg

I tried a relevant option in AutoStakkert regarding vertical line noise to see if I could fix that, but it returns completely white images...

Are these lines normal or something is wrong with my ASI290? And HAVE YOU ANY IDEA HOW TO TEST THE CAMERA?

All the best,
Alexandros


I get vertical line noise occasionally on my images too using AviStack.


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Astro-Tech AT72EDII with Altair solar wedge
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Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

DeepSolar64 wrote: ↑Sat May 15, 2021 10:37 pm
I get vertical line noise occasionally on my images too using AviStack.
Hi James.

Is it with ASI178MM that you get this noise? Is it like in the photo that I uploaded when you zoom a lot, or you may have it even at 100% size?

All the best,
Alexandros


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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

MalVeauX wrote: ↑Sat May 15, 2021 8:38 pm
C8's are nice, but for solar, you need really great seeing conditions to resolve things with 200mm aperture.
Thanks Marty, you and other kind folks here made this clear to me since the beginning, this is why I opted for buying a Lunt, rather than buying DERF and H-Alpha for the C8, given that the seeing is very rarely at the level needed.

All I wish to achieve is to be able to get Hi-res WL photos like yours (and others') with the C8 those rare times that the seeing will be perfect at home or up in the mountains. :-) Hi-res will make a change from time to time from the Lunt130 (stepped down or not). Exactly like you do, although as far as I understand you have some of the better seeing conditions among people in this forum, apart the great experience to exploit them. My understanding is that Christian has shown that unbelievable results are possible if you look for them (even at the top of the mountains) and you plan them carefully (or scientifically might be an even better word).

Step by step, I hope experience and improvement will come one day.

All the best,
Alexandros


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Lunt 130MT+1800BF, C8 Ultima PEC+AstroSolar, Skywatcher Mount EQ6-R Pro
Baader Solar Prism, ZEISS Abbe Barlow 2x, Celestron Barlow 2x Ultima Series
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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by H-Alpha »

MalVeauX wrote: ↑Sat May 15, 2021 2:30 pm
Gravel, rocks and sand can be a heat sink. Often a tarp is used as another barrier on the ground. Some people spray the ground with water around them (obviously not an option up in the mountains).
Marty what kind of tarp (and color) would be good to use? Perhaps it could also help on a balcony? Do you have any example in mind that people have used for this purpose?

Best wishes,
Alexandros


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Baader Solar Prism, ZEISS Abbe Barlow 2x, Celestron Barlow 2x Ultima Series
ZWO ASI290MM, ZWO ASI1600MM Pro,
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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by DeepSolar64 »

H-Alpha wrote: ↑Sat May 15, 2021 11:06 pm
DeepSolar64 wrote: ↑Sat May 15, 2021 10:37 pm
I get vertical line noise occasionally on my images too using AviStack.
Hi James.

Is it with ASI178MM that you get this noise? Is it like in the photo that I uploaded when you zoom a lot, or you may have it even at 100% size?

All the best,
Alexandros


I have never noticed it in a full sized image but after I downsize it yes. Not not on all images though. I do use a ASI178MM camera.


Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
Celestron AstroMaster Alt/Az Mount
Meade Coronado SolarMax II 60 DS
Meade Coronado SolarMax II 90 DS
Meade Coronado AZS Alt/Az Mount
Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
Sky-Watcher AZGTI Alt-Az GoTo mount
Cameras: ZWO ASI178MM, PGR Grasshopper, PGR Flea
Lunt, Coronado, TeleVue, Orion and Meade eyepieces

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Re: AR2822 WL (High Res), CaK, HA | May 14th 2021

Post by MalVeauX »

H-Alpha wrote: ↑Sat May 15, 2021 11:25 pm
MalVeauX wrote: ↑Sat May 15, 2021 2:30 pm
Gravel, rocks and sand can be a heat sink. Often a tarp is used as another barrier on the ground. Some people spray the ground with water around them (obviously not an option up in the mountains).
Marty what kind of tarp (and color) would be good to use? Perhaps it could also help on a balcony? Do you have any example in mind that people have used for this purpose?

Best wishes,
Alexandros
I don't use one on the ground (I stick to grass and raised up in my observatory when not mobile but I mostly stay within my observatory for imaging), but I do on walls and roofs from time to time. I'd get one of those durable tarps meant to cover RV's in straight up white color. I use this kind of tarp on the roof of my observatory even and it holds up against all the weather (including hail so far). Same principal as anything else regarding heat, darker colors will get warmer, white will stay cooler. Emissivity is key and/or reflection.

I use one of these for lots of this kind of application at my observatory:

https://www.amazon.com/gp/product/B0157J21OQ/ref=

Very best,


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