How to double stack a Lunt CaK Module? And ERF?

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How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Mon Aug 20, 2018 8:22 pm

Hello,

I'm literally obsessed with Calcium. I don't know why. I just love the way it looks. But, I want to see if it's possible to take it step farther with some tinkering. I'm sure someone has fooled with this stuff. I've been back and forth between Lunt & Quark for calcium and while I thought I was going to get the Quark, I waited, and now I'm glad I did, because I think I'll never get what I ultimately want from the Quark version. I ultimately want to be able to image calcium prominences with a 6 inch refractor.

So currently a Lunt CaK module runs $1000 for a B1200 model (straight through, I don't want diagonals).

Is it possible to some how stack two of those? That should be tight enough to see good prominence separation right? I would love to get it tight enough to see filaments in CA and proms in CA, with a surface and sunspots in CA. I've seen images of this and they're really interesting to me. Is this possible with two Lunt CaK modules stacked? Anyone have information on how to stack these?

Or, if something else is to be used to stack, what?

Also, for an ERF, since it would be to get up to 150mm aperture (refractor), I've been able to use a Baader 2" blue CCD filter with IR block as an ERF for a few months now with 150mm aperture and it handles the thermal load great. Would this be a suitable ERF in the focuser before the Lunt module to handle the 150mm aperture appropriately? If not, what would be an ideal ERF here?

Thanks!

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by marktownley » Tue Aug 21, 2018 7:44 am

Easy. Get 2 Lunt CaK filters, keep one intact, the second you need the 12mm eyepeice holder filter (in the case of b1200), stack it in the ep holder of your first intact lunt CaK filter.

You can see prominences with a ss CaK in good sky conditions (transparency) and assuming your gamma is kept neutral when recording. Filaments are visible sometimes in DS.

You will get considerably better results in CaK by only using an aperture that matches your seeing conditions instead of just trying to use the biggest scope possible. Use Christians CaK images as reference, he uses 150mm, if you can''t match the resolution (as a result of seeing) he gets back off to a smaller aperture.

ERF you are proposing should work, I would use extension nosepeices and mount it as high up the tube as feasibly possible.
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Tue Aug 21, 2018 12:18 pm

Thanks Mark!

I don't suppose you know of a resource, like a picture even, of how to stack the eyepiece holder into the intact module?

I've definitely been watching Christian's stuff, unfortunately I can't find Barrs Associates filters to match up to another filter type, like the Lunt, and PST CaK etalons are unicorns these days.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Tue Aug 21, 2018 2:54 pm

Hrm, I'm curious if KG3 vs KG5 would be useful behind the Blue CCD IR block filter to eliminate the last bit of heat without greatly effecting transmission? I've used KG3 in the past. From the transmission lines, it looks like KG5 blocks even more IR, so in theory, that should absorb even more heat right?

I also have a 2" skybender unit. I'm thinking of trying to incorporate one of the Lunt modules in it some how to add tuning to this. Not sure if that would be useful or feasible.

I could push far up the focuser with extensions to put the baader blue CCD filter as an initial ERF way ahead in the light cone, then after that, maybe a KG3 or KG5 to further handle any remainder heat. After that, the first calcium module. Then go from there.

That should handle greater than 4 inch apertures I imagine, since I'm currently using that blue ccd ERF filter and a 370~395nm pass filter and it reduces thermal load from my 6 inch aperture very nicely. So looking to see what can replace that 370~395nm filter, such as KG3 or KG5 for instances where I want to not use that filter perhaps.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by Bob Yoesle » Tue Aug 21, 2018 3:57 pm

I don't suppose you know of a resource, like a picture even, of how to stack the eyepiece holder into the intact module?
You can ditch the Skybender and just put the second Lunt CaK filter in a 1.25 " filter holder, and put that on your camera's C mount adapter.

A couple of things - your optical system's f ratio should be about f/10 or greater even for the relatively wide (compared to H alpha) CaK band-pass. This is especially important if you plan on tilting most or all the filter components. You only want to tilt the filter(s) a couple of degrees at most to eliminate reflections - you are not tuning them per-se. For my system, I'm planning of 4 degrees of tilt for the blocking components, and 0 - 2 degrees for one or both the CaK filters themselves.

The Badder Blue CCD passes considerable energy from 400 - 500 nm, so additional filtering is needed there. I will be using a Edmund 400 nm short-pass OD 4-5 filter, along with a Badder CaK wide-band filter. Others have done other combinations for similar blocking. Since my PST filters are rare (and essentially irreplaceable) I'm Mr. overkill when it comes to the out-of-band blocking, including IR, hence adding a KG3. The order of the Pre-CaK filters is not set in stone:
CaK module.jpg
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Tue Aug 21, 2018 4:11 pm

Thanks Bob, that is very helpful and answers a lot! So it appears going for a KG3/5 is definitely worth while.

Do you think KG5 would be better at blocking down more IR and reducing thermal load even more? Maybe I read the graph incorrectly or I missed something?

Now I'm curious how to handle all that tilting in there? Yowzers!

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by Bob Yoesle » Tue Aug 21, 2018 5:44 pm

KG 3 v. KG 5 is a balancing act. KG3 has slightly better transmission for DSing both CaK and Ha, and slightly higher far IR blocking. For the long IR KG3 is about OD4, while KG 5 is OD5 - not sure this matters that much, and I am preferring the higher transmission. Others might feel differently, but I don't see BelOptik using KG5, even though he could...

BTW, note the sensitivity of KG glass to UV, so having it follow the B CCD filter is a good idea:
KG3 v KG 5 SM.jpg
KG3 v KG 5 SM.jpg (455.57 KiB) Viewed 966 times
For tilting I had some circular wedges machined to fit a standard 1.25" filter holder. Now trying to get these anodized flat black...
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Tue Aug 21, 2018 5:55 pm

Great Bob, thanks! Makes a lot of sense. Looks like KG3 is the way to go, higher transmission, will still reduce the thermal load significantly.

Looks like EdmundOptics has 2" diameter KG3 filters for about $70. Not too bad. The Baader Blue with IR block with the KG3 should pretty much nuke enough of the heat in smaller apertures that everything behind them should be safe (except eye balls of course) while keeping good transmission.

When mounting the KG3, do you think leaving it slightly loose to have room to slightly expand is preferred, or tighten it down (not super tight, but tight enough to not wiggle or knock around)?

Any recommendation for a 50mm filter holding cell? They seem to run $20 but surprisingly they're not just for sale everywhere and not sure about the threading and stuff.

And, more dumb questions, trying to figure out what to call a 2" filter threaded tube that can thread into the end of an extension and inserted into the focuser to put a 2" filter deeper into the light cone, accessory tube or something? Hrm, or rather, this seems to be a 2" barrel extension, like a 2" eyepiece barrel extension.... I think?

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by Bob Yoesle » Tue Aug 21, 2018 8:47 pm

Not a good idea to have anything solar tightly secured, slightly loose is preferable.

Nothing is a simple to do project in solar filters. REPEAT AFTER ME - NOTHING WILL BE SIMPLE. You won't find a 50 mm filter holder fitting these filters to standard 2 inch astronomy filter holders. You'd have to have the filters turned down to about 46 mm in diameter or so, and it's an iffy and expensive proposition to get this done. So you have to do a lot of MacGyvering - which is part of the fun - right?!!!

For my system I'm fashioning most of the tubing and large filter retainers myself - Online Metals is your friend here:

https://www.onlinemetals.com/
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Tue Aug 21, 2018 8:52 pm

Haha, thanks Bob :)

Funny enough the past filters I ordered, 25mm filter, from Newport (KG3 filter) and it dropped right into a basic 1.25" filter cell and I just turned the ring inside it and it housed great. Worked right into everything truly simply. Just couldn't handle the heat because I was dumb hah.

I see your point about getting a 50mm but it not fitting into a typical cell. Boo!

I was thinking of just harvesting some GSO 2" filter cells. They're dirt cheap. I have the 1.25" versions laying around, and the inner cell threads out, and a new filter can be dropped in. I'm curious if the 2" does the same. But, as you pointed out, a 50mm glass filter is probably too big to drop into these filter cells. Rats.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Tue Aug 21, 2018 9:00 pm

I emailed edmund optical to see if they can help me out with respect to filter cells or sizing, etc. Hoping for a convenient solution! hah!

I'd be quite happy with a 2" baader blue CCD filter and a 2" KG3 filter at this point, as it would handle the thermal load for most applications in my largest refractor (6 inch). I suppose a hershcel wedge would do the same thing for the most part though honestly. I'm curious about it all, to be able to adapt from 393nm to 430nm with the same system, since the blue ccd filter passes 430nm fine too. Could function for both wavelengths. hrm....

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by Bob Yoesle » Wed Aug 22, 2018 1:42 am

I'd be quite happy with a 2" baader blue CCD filter and a 2" KG3 filter at this point, as it would handle the thermal load for most applications in my largest refractor (6 inch). I suppose a hershcel wedge would do the same thing for the most part though honestly.
To the best of my knowledge, the CaK filters once used by Coronado Tucson and now Lunt are not etalons or traditional dielectric filters, but instead are dichroic multi band filters, which just happen to have a small but significant peak at 394 nm. The PST CaK filters have a distinct yellow color, meaning they have significant transmission in the 400 - 500 nm range or so. It may look something like this:
Dichroic CaK.jpg
Dichroic CaK.jpg (53.96 KiB) Viewed 892 times
All we need the filter for is the relatively insignificant 394 narrow band transmission peak, and must get rid of everything else. So while a wedge may work to reduce the intensity of all wavelengths, you still need some additional filtering in addition to the CaK narrow pass element(s). The Blue CCD again passes too much in the 400 to 500 nm, and you'd need the Baader CaK wide-band filter acting as a blocking filter or similar short-pass cut-off filter to block out-of-band energy and protect the downstream element(s). A B CCD and KG filter alone won't cut it.

Again, unless you are prepared for the long haul of filter brewing, getting a Lunt module or two might be more efficacious, combined with one of Valery's or BelOptic's (future - https://beloptik.de/en/erf-energy-rejection-filter/ ) dual-band ERF's for a larger aperture.

ERF - objective or Objective - sub-diameter ERF, Lunt CaK module...
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Wed Aug 22, 2018 2:53 pm

Thanks Bob, yea I was thinking if all else, a wedge handles thermals, then use whatever narrowband filter to get what you want from it after that. But ultimately, I don't a wedge, I'm 99% imaging, so I have no need for diagonals and extra stuff if not needed, and would rather keep higher transmission for every last drop.

I have something in the works, so will see what I can do. If things don't work out, I'll probably get a Lunt CaK module and at least start with it and then try to nab a 2nd one used perhaps. Not sure. I kind of want to go ahead and get the B1800 to have more options with larger sensors in the future, though I rarely see those used, usually smaller ones only, and they're nearly unicorn status too at this point.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by Merlin66 » Thu Aug 23, 2018 8:25 am

I thought the Baader CCD-D was a good ERF for the CaK....
I need to put it on the spectrograph to see what if any the transmission is >400nm.
I’ll post the results......
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by TheSkyBurner » Fri Aug 24, 2018 2:26 pm

Merlin66 wrote:
Thu Aug 23, 2018 8:25 am
I thought the Baader CCD-D was a good ERF for the CaK....
I need to put it on the spectrograph to see what if any the transmission is >400nm.
I’ll post the results......
Its a great stage1-erf and has transmission at 90%+ at 393nm, but you have a crazy bit of off band wavelength greater than 400nm. It goes all the way up to the 500nm O3 line and cuts at 505nm
Untitled.jpg
Untitled.jpg (23.06 KiB) Viewed 843 times
The only way to cut that excess energy down without killing your transmission to 3% is with a secondary erf; A 387/10nm filter or 392/10nm filter; and if you are going that route you dont need the 400nm b-ccd filter. This is the equivalent to the "ITF" on a h-alpha pst, and is called the Induced transmission filter at this point and not erf...

What makes the b-ccd filter most attractive is that it is way under priced, even on that 50mm x 50mm square..

check out www.semrock.com They have very nice spectral plots.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by TheSkyBurner » Fri Aug 24, 2018 7:35 pm

I am going to add this here just to show you the "train".

A calcium system operates no differently than an h-alpha system, in that you have an two pre filters, the first one to eliminate major out of band color. In this instance, the blue filter eliminates red and green.

the second one to induce the transmission at the desired wavelength, AFTER the red and green is cut. So in this instance you want the center closest to 393 as possible, with the highest transmission and no more than 30nm of bandwidth. That would be the 392/10 or 387/10 or 394/10, anything will work really. a 390/10, even your 375/25.

You can add a third filter to get rid of IR and UV further(it is NEVER eliminated to ZERO, its ALWAYS there just below .007%), and third filter would be the the kg1/kg2/kg3/kg5 glass or b&w 486 filter.

The point is to just get a really clean solar transmission onto your "primary imaging filter",. That would be the narrowest filter you have, which would be the double stacked calcium skybender.

The only reason you are not mounting the calcium filter itself on the objective is because it is not full aperture. Realistically you COULD do it, and operate the thing at like f/100 just to get a crazy full disk.

Now the blocking filter, is just a standard ultra-narrow bandpass(10-angstroms or less) to cuts the bandwidth way down below 50%. This trims off the wings by half, which is intended to lower the out of band pass range within a very thin segment.
(Think 656.19 - 656.31) These do exist for calcium filters (393.4bp1 @ 3%-40% transmission from andover), but you would not want to cut your transmission to visual levels on a calcium system when you are interested in high resolution/high magnification.
012-_2__1_2.jpg
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Fri Aug 31, 2018 1:32 am

Testing out another CaK option, using a PST CaK filter and some other filters.

150mm F8 refractor used, with 3x barlow and ASI174MM camera for everything.

Didn't get to image much due to storms (Florida... sigh).

1 - 370~395nm UV filter & Baader Blue CCD Filter (white light, near UV). This is mainly to show convection cells and white light. This is actually just an ERF system (two ERFs in this case).
370~395nm_NearUV_Only..jpg
370~395nm_NearUV_Only..jpg (385.8 KiB) Viewed 706 times
2 - 370~395nm UV filter & Baader Blue CCD Filter (ERF 1 & 2) with the PST CaK filter to go narrowband and see the chromosphere features.
370~395nm_NearUV_PSTCaK.jpg
370~395nm_NearUV_PSTCaK.jpg (1022.61 KiB) Viewed 706 times
3 - Chroma 393.4nm 1nm filter & Baader Blue CCD Filter. Again, two ERFs basically. The Chroma filter is 10A though, much more narrow than my 370~395nm, but still not quite narrowband. But it still shows different features at 393nm. It's narrow enough to eliminate convection cells as it starts to bleed into the mix between the chromosphere and photosphere with just this filter. These are again just the ERFs, but they induce the 393.4nm frequency.
3934A_Chroma_Filter_Only_02.jpg
3934A_Chroma_Filter_Only_02.jpg (509.92 KiB) Viewed 706 times
4 - Chroma 393.4nm 1nm filter, Baader Blue CCD Filter and the PST CaK filter. Going narrowband, and even less leaking and a bit more contrast using the chroma filter over the UV filter I was using. Transmission is getting low, at this resolution. Going double-stack would be very difficult, as the transmission goes down heavily. Not sure it would be feasible to image with a double stack like this. Still interested though.
3934A_Chroma_PSTCaK.jpg
3934A_Chroma_PSTCaK.jpg (882.46 KiB) Viewed 706 times
+++++++++++++++++++++++++++++++++++
370~395_BaaderBlue_NearUVERF.jpg
370~395_BaaderBlue_NearUVERF.jpg (116.1 KiB) Viewed 706 times
chroma_3934A_erf.jpg
chroma_3934A_erf.jpg (124.49 KiB) Viewed 706 times
Skybender_PSTCaK_HighRes.jpg
Skybender_PSTCaK_HighRes.jpg (122.42 KiB) Viewed 706 times
highres_CaK_setup.jpg
highres_CaK_setup.jpg (128.96 KiB) Viewed 706 times
++++++++++++++++++++++++++++++++++++

And then the storms came:
game_over_08302918.jpg
game_over_08302918.jpg (44.99 KiB) Viewed 706 times
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Fri Aug 31, 2018 2:38 pm

Here's a new question with the Lunt modules:

Does it really matter what size Lunt CaK module you get if you're removing everything other than the narrowband element itself? I assume the element is the same size in all the modules and the blocking filter is what's different? I'm trying to wrap my head around what's actually in the module. If you've got adequate energy rejection in front of the narrowband element, you can just use the narrowband element, right?

I'm having trouble finding what's actually in the lunt modules.

I'm sure there's a breakdown of the module somewhere, just can't seem to find the right thread. From what I found searching, there's two hot mirrors and then the Lunt filter stack. I'm just unsure what the stack is. I would think getting two CaK B1200 modules (straight through) and removing the hot mirrors and putting the actual narrowband elements together after a sufficient ERF would do the job. It's just odd to me that there's so little out there regarding Cak and double stacking and stuff.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by bart1805 » Fri Aug 31, 2018 9:45 pm

I think this is what you are looking for.
viewtopic.php?f=9&t=24205&p=218274&hili ... de#p218274

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Fri Aug 31, 2018 9:55 pm

Thanks, that's very helpful!

Very best,

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by marktownley » Sat Sep 01, 2018 10:45 am

The important bit you need in the Lunt CaK module is the small filter in the eyepiece holder - this is 6mm in the B600, 12mm in the b1200 - you get the idea. The two filters in the nosepiece end that goes in your scope are just pre - blockers, they are similar to all the 390nm filters etc you and Apollo have been trying.

I found 2 things important with my double stack CaK mod, that was the spacings of the respective filters to avoid reflections and sufficient out of band blocking.
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Sat Sep 01, 2018 1:57 pm

marktownley wrote:
Sat Sep 01, 2018 10:45 am
The important bit you need in the Lunt CaK module is the small filter in the eyepiece holder - this is 6mm in the B600, 12mm in the b1200 - you get the idea. The two filters in the nosepiece end that goes in your scope are just pre - blockers, they are similar to all the 390nm filters etc you and Apollo have been trying.

I found 2 things important with my double stack CaK mod, that was the spacings of the respective filters to avoid reflections and sufficient out of band blocking.
Thanks Mark, very helpful! I'd love to see an image of your setup if it's no too much trouble. Not a lot of folk out there with double stack CaK going on!

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by marktownley » Sat Sep 01, 2018 3:50 pm

I'm not at home now, so away from the scopes, but here is a shot where you can see the skybender module which houses all the filters in the back of a 40mm f10 ota at an outreach event I did in August.
39091787_847155202340408_1490473992400666624_n (1).jpg
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Re: How to double stack a Lunt CaK Module? And ERF?

Post by bart1805 » Tue Oct 16, 2018 9:56 pm

MalVeauX wrote:
Tue Aug 21, 2018 8:52 pm
Haha, thanks Bob :)

Funny enough the past filters I ordered, 25mm filter, from Newport (KG3 filter) and it dropped right into a basic 1.25" filter cell and I just turned the ring inside it and it housed great. Worked right into everything truly simply. Just couldn't handle the heat because I was dumb hah.

I see your point about getting a 50mm but it not fitting into a typical cell. Boo!

I was thinking of just harvesting some GSO 2" filter cells. They're dirt cheap. I have the 1.25" versions laying around, and the inner cell threads out, and a new filter can be dropped in. I'm curious if the 2" does the same. But, as you pointed out, a 50mm glass filter is probably too big to drop into these filter cells. Rats.

Very best,
Hi Marty,
A standard 1,25 inch filter cell where a 25mm filter (like the #1 pst filter) can be housed without any difficulties. I am interested! What filter cell is that and do you have a picture of it?
Thanks in advance, Bart.

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Re: How to double stack a Lunt CaK Module? And ERF?

Post by MalVeauX » Wed Oct 17, 2018 1:02 am

bart1805 wrote:
Tue Oct 16, 2018 9:56 pm
MalVeauX wrote:
Tue Aug 21, 2018 8:52 pm
Haha, thanks Bob :)

Funny enough the past filters I ordered, 25mm filter, from Newport (KG3 filter) and it dropped right into a basic 1.25" filter cell and I just turned the ring inside it and it housed great. Worked right into everything truly simply. Just couldn't handle the heat because I was dumb hah.

I see your point about getting a 50mm but it not fitting into a typical cell. Boo!

I was thinking of just harvesting some GSO 2" filter cells. They're dirt cheap. I have the 1.25" versions laying around, and the inner cell threads out, and a new filter can be dropped in. I'm curious if the 2" does the same. But, as you pointed out, a 50mm glass filter is probably too big to drop into these filter cells. Rats.

Very best,
Hi Marty,
A standard 1,25 inch filter cell where a 25mm filter (like the #1 pst filter) can be housed without any difficulties. I am interested! What filter cell is that and do you have a picture of it?
Thanks in advance, Bart.
Hi Bart,

I have a generic 1.25" filter cell holder, it's unmarked. It had the old KG3 filter in it that I broke. I bought a KG3 filter frow NewPort, it's 25mm (25.4mm). It drops right into the cell and fits perfectly. I took a run of the mill GSO 1.25" polarizing filter as a donor filter cell to test, and it works perfectly too and that's a standard common filter cell. And the 25.4mm filter drops into that cell and fits fine too. So they're the same size, the generic one and the cheap GSO one. I'll get some photos up Thursday when I get off work.

Very best,

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