Possible to combine a Lunt CaK module with a Herschel wedge?

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thesmiths
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Possible to combine a Lunt CaK module with a Herschel wedge?

Post by thesmiths » Thu May 15, 2014 1:30 pm

I have a B1200 Lunt CaK inline module and also a 2 inch Lunt Herschel wedge. It seems to me that the Lunt "Ca-K Module for the LS152THa" is somehow a modification/combination of these two elements. Presumably a lot of or most of the front energy rejection filters of the B1200 have been left off.
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Lunt 152
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Lunt Cak inline
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Lunt wedge
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The rear CaK module for the LS152 is a set unit that can be separated from the focuser and a normal Lunt Herschel wedge can be inserted for white light use. Unfortunately, that CaK/wedge element is not sold separately from the focuser, as far as I'm aware. I am actually a little worried about the long-term wear and tear on the normal B1200 CaK module even with a 4 inch refractor. But I wanted to try it with a 140mm refractor I also own. So therefore the interest in using a Herschel wedge in front of it.

I was inspired by this project by Mark's usage of a Herschel wedge with his PST CaK mod. It seemed like a good idea, particularly with large apertures, and I guess this is the approach Lunt also took with CaK for the LS152.

I don't really know the sequence of filters in the B1200 CaK, although I assume this has been investigated here in the past (hasn't everything under the Sun been totally dissembled and dissected by someone here?). Knowing what is inside the Lunt CaK inline module would be a sensible place to start to determine if such a mod makes sense and is doable.

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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by swisswalter » Fri May 16, 2014 4:42 am

Hi Douglas

the B1200 contains 2 hott mirros followed by a tiny filter stack which sorts out the interesting reagion ¨393 nm. If you work with a herschel wedge then use only the LUNT filterstack and a K-line filter
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by thesmiths » Fri May 16, 2014 1:59 pm

Walter, thanks for that. I looked at the marketing photo for the Lunt60-CaK and it suggests there are 3 elements before what you call the "Lunt stack" and a UV cut filter after it. Or is this picture outdated?

If the first two elements are "hot mirrors" for IR, is the third one for visible and/or UV?
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by swisswalter » Fri May 16, 2014 4:50 pm

Hi Douglas

we only too apart a B1200 wedge straight through, see your pic #2, in there are only 3 elements as said. 2 hot mirrors and small filter stack about 12 mmm. The plots from these parts are recorded in the mod section, just further down
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by marktownley » Fri May 16, 2014 6:05 pm

I will dive into this discussion Douglas, but I have more than I want to say than time allows me to type right now - I will input over the weekend when work calms down a bit :)
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by thesmiths » Fri May 16, 2014 11:49 pm

Walter, I partially took apart my B1200, which is a straight through (like in the photo above). I unscrewed the long front section and it came off as a single unit very easily (no allen keys necessary surprisingly). There are two sets of screws in the long nose section, but the position of them suggests to me that there are actually 3 filters in there, a single front one and two at the back. But I could be wrong about that. I did not want to remove the "ERF" filters since I thought they might be tilted in a precise way to reduce reflections.

But you are absolutely right, there is nothing else behind the nose section except for the square yellow "magic stack", held in place by a plate. It is also easily removed if you have a lens spanner (which I do have for cleaning old camera lenses). The square yellow filter is held in place to a big chunk of metal, which is quite bulky and would lead to connection problems and back focus issues. Do you simply take the yellow filter stack out and mount it separately or you use it in the Lunt 2 inch to T2 holder it came in?

When I look through the "ERF" nose section at a bright halogen light, the colour is actually a nice violet. So the nose piece is obviously cutting not only red and IR (as would a typical "hot mirror") but also yellow, green and even some blue. I wonder, therefore, why an expensive filter like the Baader K-line is necessary as a pre-blocker after a Herschel wedge. I did a preliminary visual experiment and qualitatively a Wratten 47 plus IR cut filter after the Herschel wedge gave a similar output as the Lunt "ERF" nose piece.

In theory, I could put any of these filters in front of one of my solar spectroscopes and look at the bandpass with respect to the Fraunhoffer lines (with resolution down to 0.25 angstrom). The Fraunhoffer lines of course provide the ultimate reference calibration for such an exercise.

For an interesting discussion of the Wratten 47 plus Astronomik L filter combination, see http://www.astrosurf.com/pellier/testofbluefilters (measurements made by Philippe Rousselle). I did try this combination once for solar imaging and it gave results qualitatively only slightly worse than the Baader K-line.

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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by swisswalter » Sat May 17, 2014 12:34 am

Hi Douglas

we took apart the whole CaK wedge and found only two hott mirrors and the stack as reportet and yes the hot mirrors let trough only deep blue/violet (see also our plots we took.

We are working with both set ups. The original wedge and just adding filters after the Magic stack and also only the Magic filter and combine them with different other filters like K-Line, PST Magic and so on. The best results so far I got with the KLUPS Combo (K-line, LUNT Wedge, PST CaK)
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by thesmiths » Sat May 17, 2014 1:16 am

Walter: by KLUPS you mean Herschel wedge -> Baader K-line -> Lunt square yellow -> PST round yellow ? So double stack of the two slightly different yellow filters?

Also, is there any significance to the PST CaK having its "ERF" after the "magic yellow" filter and the Lunt having its "ERF" before the "yellow stack"?

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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by swisswalter » Sat May 17, 2014 7:19 am

Hi Douglas

I use the KLUPS filter without a herschel wedge up to 140 mm (from objetiv to CCD) LUNT wedge, K-Line_PST, CaK filter only, UV/IR cut Beloptik). I have not yet tried out all the possibel combinations but will Report one after the other
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by thesmiths » Tue May 20, 2014 4:26 pm

Walter: Did you mention somewhere that you only use half of the Baader K-Line filter? Why not use the complete double stacked filter? Does it attenuate too much? I thought it was supposed to be 390-398nm.

Mark: do you also only use half of the Baader K-line filter in your PST CaK mod?

On a related note, does the double stack Baader continuum filter bring any advantages to "white light" imaging over the single stack? I didn't think in that part of the spectrum it would make much difference.

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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by swisswalter » Tue May 20, 2014 5:30 pm

Hi Douglas

using a half K-line is only out of practical reasons. I need the thread to mount the CaK PST filter on to it. If I use the double stack, there are no more threads left to add the CaK PST filter
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by Valery » Wed May 21, 2014 1:52 am

thesmiths wrote: On a related note, does the double stack Baader continuum filter bring any advantages to "white light" imaging over the single stack? I didn't think in that part of the spectrum it would make much difference.
There will be only problem with adding of a second Baader continuum filter. No any gain in details, but it will decrease a light = increase the exposures. Increasing exposure leads to worser atmosphere freezing.

The Baader continuum filter ideal is:

1. Most of refractors are about null corrected (for spherical aberration) at this wave length - 546nm/ So, the images with achromats will be the most sharp at this wave length.

2. Reasonable sun light attenuation.

3. Earn money on a flat place. Because any deep green filter will be just the same effective for imaging in a continuum.
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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by swisswalter » Wed May 21, 2014 4:18 am

Hi Douglas

don't worry using a double stack continuum filter. It comes in one housing and works perfect with a herschel wedge
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: Possible to combine a Lunt CaK module with a Herschel we

Post by marktownley » Fri May 23, 2014 5:36 am

For this to work Douglas, you need the yellow square filter after a Baader K-line, both of which would be in the eyepiece holder of the Lunt wedge, which, must have no ND filters in situ. I would not recommend this setup for visual, but for imaging most certainly works.

I have used one half of the k-line briefly in my 'trials' but now use it with both elements.
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