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Thread: Help with 2" to 1.25" Adapter for older Lumicon Solar Filter

  1. #1
    Cargeena2's Avatar
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    Default Help with 2" to 1.25" Adapter for older Lumicon Solar Filter



    I've stated many times how great it has been to live right next door to whaat I would call a professional astronomer.
    He has been in Astronomy for many years & owns a 3 inch & a 4 inch set of Unitron telescopes plus a nice Advanced VX 6 refractor.
    We view quite often together & he has taught me more in the last year than I could have learned in maybe 5 years.
    Anyway, he has graciously bestowed upon me a 2 inch threaded Lumicon Solar Prominence Filter & a 3 1/2 inch piece of red solar glass to be installed as follows.
    I will be using another OTA telescope tube cap like the stock one I have now.
    I need to cut a 2 inch inch hole about 1/4 inch away from the edge of the cap then affix the red solar glass to the inside of that cap with either clips or mild glue.
    The reason for that 2 inch hole cut into the to raise the f ratio on my Mak to a bit more than double to view solar prominences. It is current about f/12.
    As Steve tells me, by using the offset 2 inch hole to allow for the typical center piece of my Mak in the front lens.
    When this modified cap is assembled, I would place it over the tube then attach the Lumicon solar filter to the back focuser tube.
    This is the issue:
    I have attached pictures that show the 3 1/2 inch red glass, the Lumicon solar filter, the back end of my Mak tube which is threaded & a brief sketch of how I'll be making the cap. I might use 1/4 inch bass wood then put felted construction paper around the edge so it will fit like a tube cap,the stock cap is a bit better to me.
    The biggest end of the Lumicon filter is threaded inside 2 inch, the Mak focuser tube is 1.25".
    Would anyone know which parts I would need to attach the Lumicon solar filter to my Mak tube?
    Maybe a 2" to 1.2 short threaded tube with threads on outer diameter?
    Or some type of T rings in those sizes that would thread to the filter & my focuser tube with the above short threaded tube?
    Any tips & help would be greatly appreciated.

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  2. #2
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    Default Re: Help with 2" to 1.25" Adapter for older Lumicon Solar Filter

    Lucky for you it's not going to fit. I say lucky, because this does not sound like a safe solar viewing setup. That red glass is not removing enough light - you can see the wood grain right through it in your picture. That is far too much light to allow to hit an eyepiece filter.

    Even assuming that the eyepiece filter is adequate to remove the harmful rays, it is right where the sun's rays are the most concentrated. That means that a very small part of the filter has to cope with all the sun's energy. What it doesn't let pass through to your eye gets converted to heat. The effect is exactly like aiming a tiny blowtorch at a single spot on the glass. The glass will eventually crack. Ad if your eye is behind it, the damage is likely to be instant and permanent.

    Do yourself a favour and buy some Baader solar film to make a proper aperture filter.
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    Default Re: Help with 2" to 1.25" Adapter for older Lumicon Solar Filter

    You will find more info here: Lumicon FAQ

    The section for you begins like this:

    Solar Prominence Filter
    Q:What is the purpose of the required Energy Rejection Prefilter component of the Lumicon Solar Prominence Filter system?

    A:To protect the human eye from dangerous solar radiation.

    Q:Why is an off-axis location required for the 58mm or 77mm Energy Rejection Prefilter?

    A:Simply to avoid obstruction by the telescope's centrally located secondary mirror. Unobstructed telescopes would not require an off-axis location for the Prefilter.

    Q:Is the Lumicon Solar Prominence Filter system safe to use on Schmidt-Is the Lumicon Solar Prominence Filter system safe to use on Schmidt-Cassegrain telescopes?

    A:Yes. The Lumicon Solar Prominence Filter system was designed to function normally on all commercial SCTs. Its 58mm or 77mm diameter Energy Rejection Prefilter stops down the SCT's aperture, effectively producing a focal ratio that lies within the optimum range to prevent overheating.

    Q:Can the Lumicon Solar Prominence Filter be used on telescopes having focal lengths shorter than 1200mm?

    A: Only if a Barlow lens is used to produce an effective focal length of at least 1200mm, and only if Lumicon's 58mm Energy Rejection Prefilter is used. The Barlow lens must be located before the delicate narrow-bandpass (1.5) filter.

    Thus, the components would occur in the following order:
    1. Energy Rejection Prefilter
    2. Telescope Objective
    3. Barlow Lens
    4. Narrow-Bandpass (1.5) Filter
    5. Eyepiece
    The piece of red glass in your pictures does not seem dark enough to be an Energy Rejection Prefilter. The issue is also discussed here.

    Be careful
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    Default

    Also, if your Mak has a silvered/aluminised secondary spot on the corrector with a baffle shade around it that's glued to the corrector, I'd be worried about how much heat the red glass passes - the main mirror may concentrate it enough to risk melting either the glue or the baffle itself if it's plastic rather than metal...

    And I agree with Keith - the red glass doesn't look as though it's going to block anywhere near enough light/heat by itself to get anywhere near a safe level.. I'd want to be absolutely certain I had all the energy rejection bits needed in place, and operating with the designed geometry... Apart from maybe melting the baffle off the corrector plate, I'd worry that the large focus adjustment range of the Mak might mean that while you're setting up you could end up with the light being much more focused at the filter than it's designed to cope with... If you're screwing things onto a refractor tube, the tube length effectively fixes how focused the light is at that point... Typically, it's going to be some way off focus, and so less intense. Bolting it on to the eyepiece end of a Mak makes it much more variable - and the closer to focus you are when the light hits the filter, the more concentrated the solar energy and the more likely bad things are to happen.

    (And I'd want to make quite sure that the front filter can't fall off and let raw sunlight in if it turns out the glue doesn't hold as well as it should - maybe some sort of sandwich arrangement so there's no room for it to shift...

    You only have one set of eyes; you really don't want to take any chances unless you're absolutely certain it's safe... It's not something you can fix if it goes wrong.
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    Default Re: Help with 2" to 1.25" Adapter for older Lumicon Solar Filter

    I agree 100% with both you & KeithBC insofar as the concerns over my eyes being damaged & the good possibility that intense heat may cause issues.
    I should have added that the glass is ERF glass but it was used in a 3 or 4 inch Unitron refractor by my neighbor I believe.
    His telescope has basically all metal parts & would be able to absorb heat better than my Mak would, no doubt about that.
    I've always been leery about looking at the Sun with my scope anyway so if I do decide to do some daytime solar work, I'll just buy the glass solar filter for sunspot activities or be thankful that my neighbor Steve & I look through his Advanced VX 6 refractor with his Lumicon & Thousand Oaks solar prominence filters.
    Thanks a bunch as always, the advice is much appreciated.
    Last edited by Cargeena2; 06-09-2014 at 06:30 PM. Reason: words spelled wrong
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    Default Re: Help with 2" to 1.25" Adapter for older Lumicon Solar Filter

    Greetings,

    Safety first is the best advice when viewing the Sun. And when in doubt, don't!

    The components shown in Carl's post is a Lumicon Hydrogen-Alpha filter unit and its ERF (red filter). It has been in storage for several years and when I purchased a new one from Thousand Oaks, I passed the old Lumicon H/A filter along. I must admit that, compared to the Thousand Oaks setup, the Lumicon's filter is not as dark. But that is what came with the H-A unit when I took delivery on it as a dealer.

    I created a 2" mask for the Lumicon ERF filter to be used on my 4" Unitron. It was necessary to create the mask for successfully mounting the filter onto my Unitron's dew shield. And the 2" mask raised my instrument to the required f/30 ratio to produce good solar prominences. I can attest that it was used on more than one occasion and with the desired success. But, as it was originally designed for a Schmidt-Cass and its plumbing, I recently opted to purchase an entirely new unit specifically intended for standard 1-1/4" fittings.

    Of course, if there is any doubt as to the safety of the device, I would recommend it be returned to Lumicon for inspection before it is used. It would only cost a bit of shipping. Better safe than sorry.

    Regards,
    Steve
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