Budget scope for visual

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gradoj
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Budget scope for visual

Post by gradoj »

I saved a 70mm celestron mini DOB from the bin and decided to try and turn it into a dedicated solar scope for visual. I removed the coating from the main and secondary, cut the back out from beneath the primary and installed a #9 welding filter.

I am fairly pleased with this little scope put together for a few bucks. I don't really get much detail visually though. I am new to solar observing so looking for advice on how to improve this setup sticking with the budget theme. Could I replace the welding filter with something that would be safe uv/Ir and give me more contrast for sun spots, etc? Thanks in advance
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Re: Budget scope for visual

Post by DeepSolar64 »

It's nice to see someone give an old scope new life by repurposing it. Is the No9 filter dark enough? I use a No14 for naked eye use. Also optically, welders filters are not usually figured well enough, or smooth enough for use as a scope filter but I have heard of them being used for really low magnification. A good glass or aluminized film type filter like Baader Astrosolar would be a better choice.

I use an Orion 70mm solar telescope with a built-in glass filter for white-light visual. Most of the time there are no spots to see since we are at sunspot minimum. However there are surprises like last weekends small spot group.

James


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Re: Budget scope for visual

Post by gradoj »

I have etched the mirrors so there isn't that much light getting through. #9 seems dark enough maybe too dark that was what I was wondering...just looking to remove uv/Ir what other filters should I be looking at. The Baader Astrosolar looks like a white light filter 100000:1 which I don't think I need.


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Re: Budget scope for visual

Post by DeepSolar64 »

What did you etch the mirrors with? There is a good article here about repurposing a mirror for solar. And yes, you are right, removing the coating cuts down on the amount of light reflected by the mirror. More than I thought. There is a lot of difference between a No9 and No14 welder's glass.

Yes. Baader Astrosolar is a white light and with your etched mirrors would almost certainly be too dark.

viewtopic.php?f=9&t=26525

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Re: Budget scope for visual

Post by gradoj »

I used ferric chloride from some pcb etching I had done years ago. Just took about an hour in a warm water bath and did a really nice job. I think it might be the same thing as iron perchlorate but I didn't have to leave mirrors in near as long. Maybe very thin coating on my mirrors or the warm water bath really speeds things up.


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Re: Budget scope for visual

Post by DeepSolar64 »

A Cometron. Reminds me of the scopes sold back in the mid-eighties promoting Halley's Comet. I especially remember the Celestron Comet Catcher, a Schmidt-Newtonian. Back in the days when Celestron was an American company. Today's Cometron like many modern scopes is a Chinese product. Initially they sucked but the Chinese have gotten much better at optical craftmanship these days.

Keep us posted on how your scope does. I too am primarily a visual observer, at least at this time.


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Re: Budget scope for visual

Post by marktownley »

Yes, ditch the welding filter. Use and UV/IR filter in the first instance, you could always add a green filter to increase contrast.


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Re: Budget scope for visual

Post by gradoj »

Can you recommend a uv/Ir filter that would be safe?


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Re: Budget scope for visual

Post by DeepSolar64 »

I am not sure for scope use but I believe welder's glass blocks both IR and UV radiation. They have to for welding use. This of course is for 1x naked eye viewing. Not sure on scope use. It's their figure, their smoothness that would give issues with a scope. It may be impossible to get a sharp image. I wish I had the knowledge on what kind of UV/IR filter to recommend. Someone on here surely has a suggestion. As far as a secondary contrast filter I would suggest a Baader Continuum filter. They have a greenish cast and are designed to boost contrast in white light scopes. They must be used in conjunction with another filter though.

James


Lunt 8x32 SUNoculars
Orion 70mm Solar Telescope
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Meade Coronado SolarMax II 60 DS
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Astro-Tech AT72EDII with Altair solar wedge
Celestron NexStar 102GT with Altair solar wedge
Losmandy AZ8 Alt/Az Mount
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Re: Budget scope for visual

Post by marktownley »

gradoj wrote: Mon Sep 09, 2019 6:29 am Can you recommend a uv/Ir filter that would be safe?
Any of the branded filters are fine


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Re: Budget scope for visual

Post by gradoj »

I am new to solar so maybe I should have asked what type of filter first. Here is an example of a Light Pollution Filter that appears to block UV but may let IR through? I don't think this would work for my needs. So a light pollution filter won't work, a notch or narrow band filter may work but not sure what frequency/bandwidth is best for visual.
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Re: Budget scope for visual

Post by gradoj »

I found this comment on the Web regarding a white light solar scope filter but haven't found one of these filters online. Anyone have any recommendations where to look for something close to this filter?

http://www.lpl.arizona.edu/~rhill/solar/soltel.html
interference filter centered on the G-Band around 430 nm (nanometers) with a 18 nm bandpass


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Re: Budget scope for visual

Post by christian viladrich »

430 nm filters are available at Edmund Optics with 10, 25 and 50 nm FWHM, and also at Andover Optics (2 nm FWHM).


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Re: Budget scope for visual

Post by gradoj »

Thanks. That helped get me started. My plan, unless someone tells me this is not safe, is to purchase a uv/Ir cut filter https://www.baader-planetarium.com/en/b ... ilter.html

And then just a variable polarizer to dim the brightness a little.

I was also looking at the oiii filters but they are a little expensive and mainly used with ccd imagers. Anyone know if they would work for visual with this setup?


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Re: Budget scope for visual

Post by marktownley »

Yup, will work.


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Re: Budget scope for visual

Post by george9 »

Sorry if I am misunderstanding, but I'm not sure I trust a random UV-IR filter to block all appropriate wavelengths bouncing off an uncoated mirror. I would want to actually know or measure the density 200nm to 5000nm. For visual, I would probably ignore light loss off the mirror and see that it drops it enough in UV and IR regardless of the coating. How much is enough? I would start with the ISO standard and the Ralph Chou articles.

The Baader UV-IR transmits 70% of the IR at 1100nm. Is that safe? I really don't know, but I know not to trust my own opinion.

Plus I wouldn't look at %, I would want to know density (% looks low on the graph, but could still be transmitting 1%).

It would be great to create a thread (perhaps this one) on what does make a white light telescope sufficiently safe. Be nice to have double coverage (like Lunt scopes).

George


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Re: Budget scope for visual

Post by marktownley »

Each (unsilvered) mirror reflects 5% of the light, so, 5% of 5% - so overall transmission 0.25% coming through the focuser.

Baader UV/IR is perfectly safe.

A polarising filter to trim brightness,

It really is no different than a solar wedge.


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Re: Budget scope for visual

Post by george9 »

That's good to hear. I really just don't have the experience. (Do mirrors reflect 5% in UV and IR, etc.)

George


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Re: Budget scope for visual

Post by allhoest »

I'm not an expert but I think that uncoated mirrors reflect IR also. At least the lower part of the spectrum.

Some solar edge supplier proposes UV/IR Cut in standard.
Your system for visual use has 5% x 5% transmission.
It should be safe enough with a commercial uv/ ir

CS
Alex


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