Calcium K blocking filter

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george9
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Calcium K blocking filter

Post by george9 » Mon Dec 24, 2018 1:13 am

This topic has been covered in various threads, but I still wasn't sure of a few things, so I hope you all don't mind if I ask here separately.

(I have Lunt B1200 CaK, and that is my main filter, but I am just experimenting separately from that. I realize that I could use the Lunt as blocking filter, but assume I didn't have that.)

Say you are building a filter based on a PST CaK #1 yellow filter. And say this is ONLY for imaging, no visual.

The KG3 acts as a UV-IR blocking filter. Does that absorb UV and IR or reflect them? And if it absorbs, isn't there a risk of it breaking due to heat?

The Baader blue CCD presumably drops the longer visual wavelengths. That must absorb non-blue, so that is at risk, too.

Then you also need a Chroma 1nm filter?

Can I use a UV-IR cut filter in place of the KG3? The Baader UV-IR cut filter clips the CaK line to the tune of 6 dB by my measurements. But I have another no-name 1.25" UV-IR cut filter that seems to pass CaK without attenuation.

And if I have a Baader K-line filter, do I need the Baader blue CCD or Chroma 1nm filter?

Why not just UV-IR block and Baader K-line? I could imagine three 1.25" filter cells in a row: UV-IR, Baader K-line, and PST #1 yellow.

For any of these combinations, what aperture should I allow without a front ERF? The Lunt allows 4".

Thanks.

George

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Re: Calcium K blocking filter

Post by MalVeauX » Mon Dec 24, 2018 2:31 am

Heya,

A single 2" Baader Blue CCD dielectric IR blocked filter will handle being an ERF for that system upwards of 150mm aperture (refractor design). I ran that exact filter as my ERF in my 150mm F8 refractor no problems. It handles it. You can put whatever you want behind it to narrow things as you see fit. So you could then follow it with your 1nm Chroma then the Lunt.

I wouldn't even use a KG3 filter in the train. It absorbs IR heat. You're way better off reflecting heat with dielectric coated filters (like the Baader).

You don't need an UV/IR block filter, the Baader Blue CCD filter already blocks IR and you want UV to pass, your system is close to UV.

Very best,

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Re: Calcium K blocking filter

Post by george9 » Mon Dec 24, 2018 3:37 am

Thanks, Marty. Right now I own the PST and the Calcium k-line but not the Chroma or the blue CCD or the KG3. So I was deciding what I would need to add.

I also have a UV-IR cut but proved it passes 393nm well. But maybe the blue CCD would be the one to add.

George

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Re: Calcium K blocking filter

Post by Merlin66 » Mon Dec 24, 2018 6:17 am

George,
I built up a CaK filter based on the Baader CCD blue filter as an ERF.
Combined with the various Omega narrow band filters it seems to work for me.
I’d recommend it.
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Re: Calcium K blocking filter

Post by marktownley » Mon Dec 24, 2018 6:23 am

A PST#1, Baader K line and UV/IR works, i've used it. Not sure i'd want to use it just as a 1.25" unit with scopes much above 60mm though. For larger apertures I use a 2" Baader Blue CCD sat higher in the light cone, never had any problems with this as an ERF.

My current double stack CaK setup is as follows (in the direction of light) Baader K line, KG3, PST#1, PST#1, Edmunds optics 387/11.

The Astronomik is the best UV/IR filter to have for CaK as it passes 393nm without attenuation.
astronomik-l-uv-ir_trans.png
astronomik-l-uv-ir_trans.png (22.15 KiB) Viewed 1206 times
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Re: Calcium K blocking filter

Post by george9 » Mon Dec 24, 2018 1:36 pm

Thanks so much, Marty, Ken, and Mark. This is exactly what I was asking.

Mark, on this one, "My current double stack CaK setup is as follows (in the direction of light) Baader K line, KG3, PST#1, PST#1, Edmunds optics 387/11," the Edmunds presumably clips the longer side of the band (down to 50% at 394.5nm according to specs) tighter than the Baader K line? That must help the PST#1, which starts heading back up pretty quickly.

And from the vendor photos, it looks like the Baader blue CCD absorbs visible light rather than reflecting it. No problems with heat and fracture? I guess not since all three of your are using it as an ERF up to at least 6".

My UV/IR cut filter is probably similar to profile to that Astronomik. But mine is only 1.25", so it can only go so far towards the objective.

George

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Re: Calcium K blocking filter

Post by Bob Yoesle » Mon Dec 24, 2018 3:22 pm

Hi George,

I think the Baader B-CCD is an all dielectric reflection filter on a clear BK7 or similar substrate, not an absorption filter.

My CaK system has and continues to evolve. And I have only done this for CaK imaging use.

Many years ago I and a few others started with a Baader Blue CCD filter as an ERF, then the Baader K line filter as a "blocking" filter, followed by the PST CaK No. 1 filter. This system works well for imaging. Even though the filter makers said it would "likely" be ineffective, I found adding a second PST No. 1 significantly improves chromopshere details and suppresses photosphere details, thereby improving contrast just as with H alpha. You can do this with your Lunt CaK filter and add the PST filter near the camera or on the C mount adapter. A little tilt might help to remove any spurious reflections...

However, holding my hand after the Baader K line filter and before the PST filter(s) revealed a lot of heat energy was making it through with my ED100 mm f9. I'm thinking this might be coming in from beyond the 1200 nm or so the Baader filters won't block, so I've incorporated a KG3 filter for suppressing this long IR out beyond ~ 3000 nm. Obviously not many imaging cameras are sensitive to this IR, but my concern is mainly protecting the rather rare PST CaK filters themselves, which are essentially irreplaceable unless you find someone who will to part with them - I'm really just quite overkill about this (especially given they were originally spec'd for a 40 mm aperture scope). And since I really have no way of measuring the actual flux below 1200 nm making it through, and the KG3 won't help protect the Baader K line filter (spec'd to be used in conjunction with the 3.8 AstroSolar film ahead) from the large amount of 400 to 500 nm concentrated energy passing through the B-CCD filter, I also have an Edmund Optics 400 nm short-pass hard-coated filter to possibly replace or supplement the Baader K line filter for this purpose.

Additionally, I also have the Chroma Technology 394 nm 0.1 nm CaK hard-coated filter, and per ChromaTech this filter should be quite robust. If you have the 1 nm version, it too should be similarly robust. This may obviate the need for the Baader B-CCD and K line filters. For my CT394 0.1 nm filter when properly tilted and configured in a telecentric system, this might result in essentially an optimized triple-stacked system with fewer overall elements if the Baader K line (a twin) filter is removed. Since the 0.1 nm version of the 394 nm ChromaTech filter is now rather expensive (~$2300.00 USD !) I think I'll feel safer leaving the KG3 (and maybe the K line or 400 nm SP) in the system. Additionally, neither of the ChromaTech filters will block beyond ~ 1200 nm going to the downstream PST filters. If I had the resources to be able to measure the actual flux amounts and wavelengths making it through each filter, I might be a little more relaxed regarding all the filters being employed - but I don't and I'd rather be safe than sorry.

Apples to apples: Single, Double, and Triple stacking CaK filters in a non-collimated and non-telecentric ED100 f9 system:
Stacking CaK effects labled.jpg
Stacking CaK effects labled.jpg (710.82 KiB) Viewed 1160 times
Good quality Andover lambda/4 KG3 filters are rather cheap insurance in solar filter systems, and I generally place it just after the B-CCD "ERF" so that it's exposed to less UV, which can lead to deterioration of these soda-lime glass filters. YMMV...
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Re: Calcium K blocking filter

Post by george9 » Mon Dec 24, 2018 5:17 pm

Awesome, Bob! Thanks. These few message tell a lot and reflect a lot of experience. The Baader blue is not overly expensive, so that's easy enough. I don't have the Chroma 1nm yet. And of course, given I have the Lunt, I don't really need any of these. Just having fun experimenting, and also planning on how to go beyond 4" with the Lunt.

George

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Re: Calcium K blocking filter

Post by Bob Yoesle » Mon Dec 24, 2018 7:28 pm

Hi George,

If I were you, I'd just add the PST to the Lunt as described, and get a pre-filter attached to the front of the Lunt module for larger aperture use:

https://www.edmundoptics.com/p/394nm-cw ... ter/19839/

or

https://www.edmundoptics.com/p/390nm-cw ... ter/28795/


I don't know how far to the IR the Lunt module is blocked, but you could give Brian a call... or you can add the Andover 50 mm KG to the Lunt module as well:

https://www.andovercorp.com/products/co ... bing-type/

Like I said, pretty cheap insurance if you don't know.
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Re: Calcium K blocking filter

Post by marktownley » Mon Dec 24, 2018 8:20 pm

Your mileage is the same as mine Bob 😉
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Re: Calcium K blocking filter

Post by MalVeauX » Mon Dec 24, 2018 10:17 pm

Hey George,

I was using the Baader 2" Blue CCD as the primary ERF for a while. I still use it for that.

I was using a 1nm Chroma filter and two PST CaK filters in a train.

The heat was totally handled from 40mm to 150mm apertures with just the Baader Blue CCD as the ERF (2") and the Chroma filter is pretty stout. And I stressed the system with the 150mm aperture often. Never had issues with heat.

Results of Blue CCD (ERF) -> Chroma 1nm -> PST Cak + PST Cak:

Image

Image

And with the 150mm:

Image

Image

Image

Very best,

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Re: Calcium K blocking filter

Post by george9 » Tue Dec 25, 2018 12:09 am

Awesome images, Marty. My Baader K-line arrived today (purchased on AM for a reasonable price). I wish there was something to image now to test it out. My main reason for trying without the Lunt is just that you don't really understand something until you do it yourself. All the vagaries of reflections, heat buildup, etc. I'll start with my 70mm stopped down to 50mm.

George

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Re: Calcium K blocking filter

Post by george9 » Tue Dec 25, 2018 1:12 am

> The Astronomik is the best UV/IR filter to have for CaK as it passes 393nm without attenuation.

Mark, careful on the Astronomik if you ever need to replace. Your graph looks like the old Astronomik UV-IR filter, which is no longer offered. Now there is an L-1, L-2, and L-3. Their literature says the L-2 is their new version of the old one, but in fact, the L-2 loses 6 dB of gain. That's what I actually own (not Baader; I was mistaken). The L-1 is what you will want instead. And the L-3 will block Calcium K entirely. I wish I knew this when I bought the L-2.

George

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Re: Calcium K blocking filter

Post by marktownley » Tue Dec 25, 2018 8:46 am

Usef Info, thanks George 👍
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Re: Calcium K blocking filter

Post by george9 » Wed Dec 26, 2018 1:04 am

Wow! Did some testing today and was surprised by the quality of the result in my R2.

I never thought to check if my 1.25" cells had threads on both ends. Out in the field, sure enough, no. The Baader K-line cannot take another filter, and neither can my PST#1 the way I mounted it in my cell. I made due to Scotch tape to hold the stack together.

Pronto (70mm f/6.8) to 2" diagonal as a spacer, to no-name UV-IR blocker (that passes 394nm well), to Baader K-line, to PST#1, to R2 video camera. Was WAY bright, so I stopped down to 50mm. In the end, I figure 10x brighter (more power) than a Lunt CaK based on 70->50 is one factor of 2, and the PST#1 at 6dB gain looked like the Lunt at 12dB gain. That's about 9dB or about 10x, I think. Makes me wonder if the Lunt is purposely attenuated to allow visual use. This was at exposures of 1/10,000 sec. Fun to see the entire filter fit in 3 small stacked 1.25'" cells.

The image looked great, a little better than my Lunt CaK B1200. Nice contrast. I do have some sad iPhone shots of my R2 screen. Yes, I will get a real camera some day.

Double stacked Lunt CaK -> PST#1 (no Baader K) was maybe a little better than the PST#1 above.

Your guys' double PST#1's must be great.

Time to get the Baader blue CCD 2" for the front of the diagonal. Then I don't need anything to screw into the Baader K. I just need to fix the PST#1 cell. (And with the Baader blue, I don't need the UV-IR. Still could add in the KG3 for good measure.) I shouldn't need the Astronomic UV/IR L1 unless I can prove it covers more of the outer spectrum than the Baader blue.

George

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Re: Calcium K blocking filter

Post by george9 » Wed Jan 02, 2019 12:21 am

I got the Baader CCD blue and it works as advertised. 92mm f/7 to Baader CCD blue to Baader K-line to ND filter to PST#1 to R2 video camera produced a nice image today. That main active region was so bright. The best image, of course, was 92mm to Lunt B1200 CaK to PST#1 to R2.

Two questions. Will the Baader CCD blue provide extra blocking for the Lunt CaK? If the Lunt's blocker is already a bandpass filter, then adding the Baader won't do much. It will just pass the intense blue light. The Lunt blocker reflects silver, so I am guessing it is a narrow bandpass filter, reflecting most of the visual light. I assume the Lunt is limited to 4" because of what gets through the blocker, not because of what the blocker reflects, but I don't know.

Given the Lunt CaK has no thread on the end, how have you all added filters in that situation? The Lunt has to be placed fairly far up the optical path for everything to come to focus, so a 2" extender is not really an option.

Also, what about the KG3? It seems to come as a 50mm disk. Any easy way to get that into a standard optical train? It's too wide for a 2" filter cell.

Seems like a bare Herschel wedge would be useful, as I am using an ND filter anyway.

A large ERF would of course be great.

George

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Re: Calcium K blocking filter

Post by Merlin66 » Wed Jan 02, 2019 12:46 am

George,
To get the Baader blue filter as far as possible up the OTA I bought a series of M48 adaptor rings, 50,30,10mm and used them to push the Baader forward.
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Re: Calcium K blocking filter

Post by george9 » Wed Jan 02, 2019 2:30 am

Thanks. I just can't think of a way to attach it to the Lunt, which has no thread at the end. I can rig up a clamp, but then it won't fit into the 2" focuser. Thin cellophane tape can hold it on, I guess.

George

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