A big solar newton for ultra narrowband imaging, possible?
Posted: Sat Aug 31, 2019 8:44 pm
The here subject cover the observing with aluminized mirror, thus having high flux suitable for Ha / Cak imaging.
Warning: Solar observation is dangerous, we know it.
There are solutions for reducing the danger: front filter, Herschell prism, de-aluminized mirror, etc. But solar observation still remains dangerous.
The here subject copes with the use of the full aperture of a telescope, partly without pre-filtering. We are clearly in a zone, where we should know what we are doing and where the dangers are. Dangers are direct (ie direct viewing), indirect (ie reflection), affecting equipment (ie reflection aside, heat-up / burning parts), etc.
If you don't know what you are doing, if you are not mastering your working process, strictly refrain for any solar scope action.
I can not take any responsibility for any action you would do in solar observation, especially with modification.
Certainly never put an eye in a moded scope
Considering again the dangers, expected and unexpected, I'll take over word by word the comments posted along my previous post:
"anyone doing this should take all necessary precautions."
"I cannot stress enough the dangers "
"Use with caution and respect!"
--------------------------
In the here trial, a 300mm aperture scope, with coating, is used.
The amount of solar power collected by the mirror is estimated to 90w. As much as a quite powerful light bulb.
The scope is of newton type, thus a big part of the heat is concentrated on a circle of about 50mm in diameter at the location of the secondary mirror, then further concentrated to the focus and forth.
We all know that there big front ERF filters are difficult to make and also very expensive. A 300mm front ERF doesn't cost a few thousand of Eur, but several thousand of Eur.
So the idea of a smaller ERF set into the system.
Here the ERF would be as big as the secondary, thus about 50mm in diameter, located in front of the secondary.
I started with various trials, measuring temperatures, etc.
You can figure what will come into these fingers...
... A blue interference filter suffering the full flux
The filter resists.
I tried also to partly target the filter, so to have one side "cold" and the other side "hot".
The filter still resists.
The wished color (blue here) passes through the filter.
The remaining flux is reflected back.
This is one of the indirect danger of the application. In this picture the flux is reflected back toward the body of the telescope, leading to a local heating. I experienced also a returning flux against the carbon truss; they started then to generate smoke.
The test filter was a 1.25" model.
Then I went for the final version, a 50mm filter.
The setup is quite artisanal. We are in the test phase.
I tried with a blue "ERF" and a red "ERF" aiming for CaK and Ha
In my area, a small city suburb, surrounded by streets and houses, I could get some granulation.
Looks "interesting" at this stage. Here in blue.
So, I went out of the city for further trials.
I could get better granulation pictures, in the red domain. In the blue, the pictures were awful.
The next step was a trial in Ha.
Here also, I could get some results, but not easily. Only when the seeing was stable. And only with a focal reducer.
Very full of hope, I went to the St Veran Observatory site, expecting for further progress.
The first results were promising. Christian detected filigrees on my first image in KLine.
But the picture quality was poor.
Finally, getting further progress was difficult.
We checked the temperature in the system with an IR camera.
Certainly, we don't know the emissivity of the filter surface, nor from the surrounding material, but it looks that hot parts to have are about 10°C higher than the surrounding.
Image courtesy Frederic Jabet.
Even the focusser side is getting warmer, sign of energy passing through the filter and heating the setup the system behind
Image courtesy Frederic Jabet.
In Halpha, the results were not better.
Now, I remember that I could get the former Halpha "reasonable" results only when clouds were passing. The clouds were leading to temporary cool down of the equipment.
An other fellow made a similar test in St Veran, with a different optic and he also had trouble getting high resolution imaging.
After one additional trial, I came to the conclusion of instrumental turbulence due to the local heat of some telescope parts, despite the system was fully open (made out of a truss system).
So, I went for removing the primary mirror coating.
Here, the first pics in bad seeing and bad wind conditions, in KLine with no coating on the primary.
I had later a chance to observe with the de-coated mirror in better seeing conditions. Here under 450nm
The conclusion is clear.
Bye Bye cheap ultra narrow band imaging.
CS
Alex
2019-Aug-31
Warning: Solar observation is dangerous, we know it.
There are solutions for reducing the danger: front filter, Herschell prism, de-aluminized mirror, etc. But solar observation still remains dangerous.
The here subject copes with the use of the full aperture of a telescope, partly without pre-filtering. We are clearly in a zone, where we should know what we are doing and where the dangers are. Dangers are direct (ie direct viewing), indirect (ie reflection), affecting equipment (ie reflection aside, heat-up / burning parts), etc.
If you don't know what you are doing, if you are not mastering your working process, strictly refrain for any solar scope action.
I can not take any responsibility for any action you would do in solar observation, especially with modification.
Certainly never put an eye in a moded scope
Considering again the dangers, expected and unexpected, I'll take over word by word the comments posted along my previous post:
"anyone doing this should take all necessary precautions."
"I cannot stress enough the dangers "
"Use with caution and respect!"
--------------------------
In the here trial, a 300mm aperture scope, with coating, is used.
The amount of solar power collected by the mirror is estimated to 90w. As much as a quite powerful light bulb.
The scope is of newton type, thus a big part of the heat is concentrated on a circle of about 50mm in diameter at the location of the secondary mirror, then further concentrated to the focus and forth.
We all know that there big front ERF filters are difficult to make and also very expensive. A 300mm front ERF doesn't cost a few thousand of Eur, but several thousand of Eur.
So the idea of a smaller ERF set into the system.
Here the ERF would be as big as the secondary, thus about 50mm in diameter, located in front of the secondary.
I started with various trials, measuring temperatures, etc.
You can figure what will come into these fingers...
... A blue interference filter suffering the full flux
The filter resists.
I tried also to partly target the filter, so to have one side "cold" and the other side "hot".
The filter still resists.
The wished color (blue here) passes through the filter.
The remaining flux is reflected back.
This is one of the indirect danger of the application. In this picture the flux is reflected back toward the body of the telescope, leading to a local heating. I experienced also a returning flux against the carbon truss; they started then to generate smoke.
The test filter was a 1.25" model.
Then I went for the final version, a 50mm filter.
The setup is quite artisanal. We are in the test phase.
I tried with a blue "ERF" and a red "ERF" aiming for CaK and Ha
In my area, a small city suburb, surrounded by streets and houses, I could get some granulation.
Looks "interesting" at this stage. Here in blue.
So, I went out of the city for further trials.
I could get better granulation pictures, in the red domain. In the blue, the pictures were awful.
The next step was a trial in Ha.
Here also, I could get some results, but not easily. Only when the seeing was stable. And only with a focal reducer.
Very full of hope, I went to the St Veran Observatory site, expecting for further progress.
The first results were promising. Christian detected filigrees on my first image in KLine.
But the picture quality was poor.
Finally, getting further progress was difficult.
We checked the temperature in the system with an IR camera.
Certainly, we don't know the emissivity of the filter surface, nor from the surrounding material, but it looks that hot parts to have are about 10°C higher than the surrounding.
Image courtesy Frederic Jabet.
Even the focusser side is getting warmer, sign of energy passing through the filter and heating the setup the system behind
Image courtesy Frederic Jabet.
In Halpha, the results were not better.
Now, I remember that I could get the former Halpha "reasonable" results only when clouds were passing. The clouds were leading to temporary cool down of the equipment.
An other fellow made a similar test in St Veran, with a different optic and he also had trouble getting high resolution imaging.
After one additional trial, I came to the conclusion of instrumental turbulence due to the local heat of some telescope parts, despite the system was fully open (made out of a truss system).
So, I went for removing the primary mirror coating.
Here, the first pics in bad seeing and bad wind conditions, in KLine with no coating on the primary.
I had later a chance to observe with the de-coated mirror in better seeing conditions. Here under 450nm
The conclusion is clear.
Bye Bye cheap ultra narrow band imaging.
CS
Alex
2019-Aug-31
