Presentation and question about Luminance filter for Daystar CAK

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davidem27
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Presentation and question about Luminance filter for Daystar CAK

Post by davidem27 »

Hello everybody,
my name is Davide from southern Italy and this is my first post in Solarchat forum.
I'm glad to be here in this specialized place over this beautiful branch of our passion, Astronomy.

Althought I play amateur astronomy since 1997, I'm a fresh newbie of the Sun affairs.

I actually have a 120mm refractor, paired by a photographic version of Baader Herschel Wedge.

I have a question for a friend of mine.
He has the DayStar Calcium K-line Quantum t-scanner module but no "hot mirror luminance filter", as Daystar suggests.

As Daystar says:
DayStar recommends use of IDAS Brand UV/IR filters in rear-mounted configuration on refractors only. The IDAS Brand UV/IR cut filter has been tested to pass 3933Å light, but reflects UV and IR light back out the front of the telescope unfocused. This application is called a "hot mirror".
It seems that there is no IDAS luminance filter except of the "Hα-enhanced UV/IR blocking Filters".

Do you know if there is any IDAS filter dedicated to this "hot mirror" application?
Or if I could apply any other Luminance filter like Astronomik L1 filter that seems to have wide wings in UV part of its bandpass?

Thanks so much in advance for your kind replies.

Have a calm and clear days.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by christian viladrich »

Hello David,
An L filter (= UV/IR cut filter) transmits about about 50% of the solar light (integrated from 280 nm to 4000 nm).
A blue filter (such as Astronmik blue CCD) transmits only 25% of the solar light. This is a significant difference.

As for myself, I use a blue Astronomik filter on my TOA 15O for Ca K imaging. However, I am not sure the new generation has a good transmission in Ca II. You have to check this with Astronomik. On the other hand, Baader B CCD is OK :

http://astrosurf.com/viladrich/astro/in ... der-AL.JPG

Hope this helps

Christian


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by davidem27 »

Thanks so much Christian!
As one of the most productive solar imager, worldwide rewoned, I do not under estimate this advice from you neither than a second.
But I'm trying to figure out why a Blue CCD filter can run up as "hot mirror" luminance filter, as Daystar requests.

Is the T-Scanner CAK module not narrow enough?

Or maybe the purpose of the hot mirror luminance filter should be to cut off the amount of not interest light before it reaches the t-scanner module, so a filter like Astronomik Blue or Baader Blue let pass the 3933 wavelength, cutting the other parts of the spectrum?

I'm going to place an order for an Astronomik L1 filter but I would like to do the best choice for a really expensive equipment like T-Scanner by Daystar.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by christian viladrich »

Hello David,

As explained, the transmission of the L filter is about 50%, while the transmission of the B filter is about 25%.
So, it is preferable to use a blue filter (for example Baader CCD) rather than an L filter. You will have a better protection for your T-scaner.

The term "hot mirror/cold mirror" refers to "simple" coating reflecting or transmitting IR. Typically, the break even point is at 700 nm (near-IR):
https://www.edmundoptics.fr/p/0deg-aoi- ... ror/19165/

But ... manufacturers can provided a much better coating for a Ca K (or H) pre-fiter. This is simply a blue CCD filter. These are readily available at Astronomik, Baader, etc. Still, you need to make sure that the transmission in Ca K is OK (OK for Baader B, not sure for current version of Astronomik B, not good for B Astrodon).

You need to place the B filter (2" diameter) as much as possible inside the OTA (away from the T-scanner). Still, you need to check there is no vigneting by the 50 mm filter. On my system (TOA 150 f/7), the 50 mm B Astronomik is about 220 mm ahead of the focus :

http://astrosurf.com/viladrich/astro/in ... onomik.jpg

Clear skies

Christian


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by christian viladrich »

BTW, this is just what you said here, by just replace "hot mirror" by "Energy Rejection Filter".
""Or maybe the purpose of the hot mirror luminance filter should be to cut off the amount of not interest light before it reaches the t-scanner module, so a filter like Astronomik Blue or Baader Blue let pass the 3933 wavelength, cutting the other parts of the spectrum?"""
The general idea is to cut down the thermal load on the (expensive) Ca K (or Ha) filter.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by davidem27 »

christian viladrich wrote: Mon Jun 14, 2021 3:45 pmBTW, this is just what you said here, by just replace "hot mirror" by "Energy Rejection Filter".
Oh! So simple...!

Thank you very much again, Christian!
I'm going to look for a Baader Blue CCD filter, just to ensure to avoid new series of Astronomik B.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by Merlin66 »

I use the 2" Baader Blue CCD filter as an "ERF" filter in front of my DIY CaK filter assembly. Works well for me.
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Re: Presentation and question about Luminance filter for Daystar CAK

Post by davidem27 »

My order for a Baader B CCD has been sent.

Thanks so much! I'll try to keep you updated.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by Bob Yoesle »

My experience with the Baader Blue CCD filter is that it lets a great deal of energy through and allows the components after it become quite warm - verified by the warmth on my palm !-0.

A more robust (and of course expensive - but worth it relative to the primary filter system) CaK ERF filter system would be the Edmund hard-coated 394 nm 10 nm bandpass filter with 85% or greater transmission, followed by a KG3 filter (~ 90% + transmission at 394 nm) for long IR suppression.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by christian viladrich »

I don't remember what is the free aperture of DayStar Ca K T-scanner ? As pointed by Bob, the EO 394-10 nm is certainly more selective than the Baader blue CCD filter. It is getting expensive in 2" aperture.
In fact, in my single stack set up,I use a 50 mm blue Astronomik filter away from the focus, and a 25 mm EO394-10 nm close to my 30 mm Barr Ca K filter.
A KG3 will certainly bring additional protection.
In any case, if we were to select only one filter, a Baader Blue CCD filter or a EO 394-10 nm would be a much better protection than an UV/IR rejection filter.


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Re: Presentation and question about Luminance filter for Daystar CAK

Post by davidem27 »

...and I got the Baader B CCD!

Daystar suggests (for +150mm scope) to to mount an Astrosolar filter in front of the optics with Cak T-Scanner
Maybe it could help, stacked with Baader B CCD...
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