Lunt CaK module bandwide?

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Lunt CaK module bandwide?

Post by Valery »

Does anybody know what is the FWHM and transmission % of the Launt CaK modules?

Thanks,

Valery.


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Valery

we have thread in here with the figures and the plot. Calculate with 2,4 FWHM and around 8% Transmission for the LUNT B1200 wedge


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Re: Lunt CaK module bandwide?

Post by Valery »

Thanks, Walter!

Note that on your graph the Lunt stack has a notable asymmetrical shape and wide of 2,4nm - again, nanometers, not angstroms!

Mark T. noted that the spectrometer you have used has only 1nm resolution. In this case if the Lunt stack has 0,24nm band wide, then this spectrometer can't resolve the profile of such narrow line.

Also, the pictures which were taken with some filters combinations with band wide significantly more than 2nm are not that far from the picture(s) taken through Lunt CaK wedge, in any case comparable and much better than through 8nm Bader CaK.

So, can you, Walter, confirm that this graph shows a real wide of the Lunt stack - 2,4nm and 8% transmission?

This month I will test our CaK filter with 2,5nm FWHM and 66% of transmission. This is 3 and 4 cavity filters, so, the wings are fully suppressed. Hope they will show good results. With special steps may be 1,5nm or even 1nm is possible for us, but not deeper.


Thanks,

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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Valery


I can confirm that this plots where made at my lab and have not been tempered at all. Well, the resolution is not what I could wish for, but I go with that what I have. For comparison it is still good. We looked also at Taiwan filters around 1 nm FWHM but they would not show fine CaK details.

The best we have seen so far is a combination CaK-PST filter with the LUNT B1200 filterstack combined. Maybe Mark has some more comments to this


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Re: Lunt CaK module bandwide?

Post by mdwmark »

The images that I have seen with the Lunt CaK look about right for around 3 Ang. I don't think you would see a difference between 2.4 and 3ang HW single cavity filters or etalon.
I know with hard coating you can get down to 1 ang single cavity. You would need to order a large batch to get the cost down. If you where to cut them down to 4mm square then you cost per unit would even be lower. For me I don't use anything smaller then 25mm filter. The most common is 38mm,this runs up the cost.
Just for a side note I did a calculation for a solid spaced fused silica etalon and found that the surface didn't need to be that tight to make a 2.4Ang etalon at K-line. So I had started with a 38mm CA with 90% mirrors with a thickness of about .047mm. The flatness was only 1/20 wave checked at 633nm with a 0.1 arc sec max tilt and you would end up with a 2.3Ang HW with 15%T. This would be plenty of light to start with before blocking. This could be the other way Lunt makes there Cak module. Either way it's going to work.

Valery: You are having 2Ang+1/-0 Ang 3-4 cavity filters made? What size of bandpass CA are you making. That design should work out very well. These filters are not going to be cheap. That narrow I would assume they are going to be hard coated. That is a tough order to keep the spacing right. Also how far in the IR do you plan to have them blocked? There are not to many company's that can make that filter right.
This will be a beautiful filter when done right.
Mark Wagner


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Re: Lunt CaK module bandwide?

Post by marktownley »

Glad you've made it back over here Mark, always enjoy your contribution to these discussions.

I would love to know some sources for these filters, even the proper name of what to ask for when ordering. The only place we found was Barr Associates, and this was several thousand pounds for 2.5a filter - cheaper to buy and mod a Lunt...


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Re: Lunt CaK module bandwide?

Post by Valery »

mdwmark wrote:
Valery: You are having 2Ang+1/-0 Ang 3-4 cavity filters made? What size of bandpass CA are you making. That design should work out very well. These filters are not going to be cheap. That narrow I would assume they are going to be hard coated. That is a tough order to keep the spacing right. Also how far in the IR do you plan to have them blocked? There are not to many company's that can make that filter right.
This will be a beautiful filter when done right.
Mark Wagner
Thanks for your comments, Mark.
The filter we have assembled from already available (ours) filters is 2,5nm 65% transmission filter. This is 4 cavities filter with very steep profile practically with no wings. However we will not test it soon as we will wait the new stack of 4 or 5 filters with 2nm FWHM and 60% each. Possibly they will allow about 1nm resulting FWHM and even more steep profile.
The size of these filters now is 15mm. No need to make larger as this will cause uneven transmission within a filter. We need to make special mechanics for making such filters maximally uniformly.
I hope that with such bandwide and steep profile with no wings will be directly comparable with 2.5 - 3A single cavity filter.
These filters are hard coated.

May be my hopes are baseless, Mark? Can you comment what can be achieved on the Sun with such filters as we trying to make affordable for amateur community? Thanks in advance for your opinion.

Also, Mark, I sent you the e-mail.


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark and Valery

very interesting discussion. We made tests on the combination K-Line double stack plus Bob1 and Bob2 stacked on to them. The result was not even reaching near the standard LUNT B1200 caK wedge. I guess the final filter has to have around 2-3 A FWHM to reveal fine CaK II details


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Re: Lunt CaK module bandwide?

Post by Valery »

swisswalter wrote:Hi Mark and Valery

very interesting discussion. We made tests on the combination K-Line double stack plus Bob1 and Bob2 stacked on to them. The result was not even reaching near the standard LUNT B1200 caK wedge. I guess the final filter has to have around 2-3 A FWHM to reveal fine CaK II details
Walter, what was the resulting FWHM, transmission of this combination of filters?

I believe, that if we will stack 4 or 5 filters with FWHM of 2nm, the results will be significantly better/ K-line (Baader?) is of 8nm band wide. 4x the difference with
2 nm FWHM filter.

BTW, I bought a PST CaK. It will arrive in a two weeks or so. This will be a good background when I will test our CaK filters.

Valery.


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Valery wrote:

BTW, I bought a PST CaK. It will arrive in a two weeks or so. This will be a good background when I will test our CaK filters.

Valery.

Hi Valery


yes that is the way to go and beat


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Re: Lunt CaK module bandwide?

Post by marktownley »

Valery wrote:I believe, that if we will stack 4 or 5 filters with FWHM of 2nm, the results will be significantly better/ K-line (Baader?) is of 8nm band wide. 4x the difference with
2 nm FWHM filter.
Yes, hear what you're saying, but the Baader K-line is just used as a smaller ERF in combination with the 2. angstrom Lunt / Coronado filter. The K-line filter is essentially just a white light filter operating at the blue end of the spectrum.

If you stack 4 or 5 2nm filters the overall transmission will drop significantly?


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Re: Lunt CaK module bandwide?

Post by marktownley »

I realised Valery when I said to drop me an email the files I was talking about i'd already uploaded into one of the CaK threads on here, but incase you haven't found them here they are again :)
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HeliographeCaK.pdf
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HeliographeCaH.pdf
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Re: Lunt CaK module bandwide?

Post by Valery »

marktownley wrote:I realised Valery when I said to drop me an email the files I was talking about i'd already uploaded into one of the CaK threads on here, but incase you haven't found them here they are again :)
Thank you, Mark! Very interesting and I am glad to know your present setup delivers directly comparable results.


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Re: Lunt CaK module bandwide?

Post by Valery »

marktownley wrote:
Valery wrote:
If you stack 4 or 5 2nm filters the overall transmission will drop significantly?
Yes, this is imminent - transmission drop. But even with five staked filters there will be a plenty light to work with.

Probably it is better to make true CaK etalons, not an interference filters.


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Re: Lunt CaK module bandwide?

Post by sullij1 »

Mark W, Glad you are back. Thanks for the design parameters! :D


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Re: Lunt CaK module bandwide?

Post by marktownley »

Valery wrote:Yes, this is imminent - transmission drop. But even with five staked filters there will be a plenty light to work with.

Probably it is better to make true CaK etalons, not an interference filters.
Just watch out for the reflections / ghosts from all these filters!


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Re: Lunt CaK module bandwide?

Post by mdwmark »

Hi group,
I am always thinking in ang's and not nm's. Angstroms is such old school. I was at an trade show and was talking to the sales person and asked if they could make a 10ang filter and he looked confused. So I changed it to 1nm then he knew.
K-line filter's has always cost more for a couple of reason. First when you are working with soft coatings the high index material is real only good from 400nm and up. One time I asked one of the engineer at Andover to make me some 1.5Ang 1 cavity like they make at Ha. He said they had tried before and it was such a pain and took so many layers that they didn't want to deal with it . The next is the investment, in the past we really didn't sell that many. Most went to schools so you would only order small batches of blockers(10Ang, 2 cavity) which runs the cost up.
Now if you change to hard coated then the cost per unit really goes up. These machines costs in the millions to start with and need to make large batches to pay for them self. Barr has gone to a mim charge of $5000 for orders for hard coated jobs.
Now if you are going to try to use 25Ang filters your only choice is the tilting game. You may be able to do it with 2 but don't be surprise if it takes 3. The transmission is going to drop fast but you are starting with 65% and cameras love K-line. Using 3 cavity filter,s is going to help also. The side bands are going to be nice and sharp. My main concern would be the design for blocking. If all the coating are on one surface then it should work. If they are using a standard design where they use another mirror for the long side blocking cemented to the bandpass then you may get internal refection.
Good luck with the project
Mark Wagner


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Re: Lunt CaK module bandwide?

Post by marktownley »

mdwmark wrote: My main concern would be the design for blocking. If all the coating are on one surface then it should work. If they are using a standard design where they use another mirror for the long side blocking cemented to the bandpass then you may get internal refection.
From where I see it the blocking is the easy bit. We now have a couple of options available; the filter stacked could be used in conjunction with a baader k-line filter and a solar wedge (with no ND filtration), or alternatively a baader k-line and a Beloptik tri-band ERF if more light throughput is required. Oliver now offers the tri-band in sizes up to 155mm on an 8.5mm thick 1/10L BK7 substrate. I have 2 in 85mm diameter, and are very happy with them.


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Re: Lunt CaK module bandwide?

Post by mdwmark »

Ok,
What is the real HW of the Lunt filter?
I did some calculations between an bandpass and a Fused Silica etalon at different F/#.
The calculations are based on a simple 1/4 wave design, no abortion,the computer makes the 1/4 wave thickness perfect. So this is not real world but it will give you an idea what is happening at different F/# and different spacer indexes.
First a bandpass with a high index spacer.

F/# Transmission wavelength HW

100 100 3934Ang 2.2Ang

20 98 3933.6Ang 2.67Ang

10 80 3932.8Ang 3.55Ang

6 45.9 3930.6Ang 7.45Ang




Fused Silica etalon

F/# transimission wavelength HW

100 100 3934Ang 2.47Ang

20 91.8 3933.3Ang 2.87Ang

10 53.9 3931.5Ang 5.73Ang

6 24 3926.3Ang 14.7Ang

So you can see by changing the F/# the wavelength shifts blue and depending on the spacer index of refraction how much the filter will broader out.
This is based on the simplest design and you are never going to have 100 transmission. But the HW's should be close and the shifting will be close also.
I hope this gives a little understanding what happens at different F/# through the filter.
Mark Wagner


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark

thank you very much. So in my words, we should use a f/20 beam or even above in order to have very good results ?


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Re: Lunt CaK module bandwide?

Post by marktownley »

Thank you Mark, some interesting food for thought there.

I have a question though, this is based on an etalon, does the same effect happen with a hard coated filter to greater or lesser degree.


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark T

perfect question which I did forgett


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Re: Lunt CaK module bandwide?

Post by mdwmark »

k-line.jpg
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Hi All,
The bandpass was a hard coated filter. I based it using Tantalum Oxide as the high index and Sio2 as the low index.
The trouble with soft coating is all the high index material start to absorb really bad at 400nm. So by the time you get to 393.4nm your working with very little light. (talking about absorbing at K-line. TiO2 which is used in a lot of broad band AR's is not doing very well below 400nm. And a lens with a 1/4wave Mgf2 coating may do better at K-line then a fancy BBAR ). Company's like Andover do make 2 cavity 5 ang and 10 ang filters that are soft coated. They can do this by there secret blend of high index martial. One of the old timers gave me a formula to try, if it works maybe I will be making .5Ang K-line filters someday.
With the new designs they would make great K-line filters but it comes down to cost per unit.
In the past people tried to use them visually and had trouble seeing anything this made them not popular. This is what has keep the cost up.

This part really belongs on the other post. But F/20 was always the F/# I would suggest using.
Valery is right about the telescope for K-line. The simpler the better. An 4" F/15 air spaced stop to 2-3" always gave the best image even at high magnification.
I even have a couple images using a video camera using a C-8 stopped to 2" off axis and they where not bad.
If the attachment went right it was with the C-8
Mark Wagner


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark


thank you very much for the inside view. How about Niobium oxide as the high index layer ?


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Re: Lunt CaK module bandwide?

Post by mdwmark »

Hi Walter,
Niobium Oxide should be good to 380nm. So it should work. It evaporated at a lower temperature 1800C.
I will look into more and get back to you. But I can't remember what the difference would be, Tantalum Oxide does work well for bandpass filters. Maybe it doesn't really matter, just what you are set up for.
Mark


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark

thank you very much


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Re: Lunt CaK module bandwide?

Post by marktownley »

Thanks Mark for this insight. It made me start thinking, so this morning I decided to do some experiments. I'm running a pair of 2.2a filters from a CaK PST in series (to in theory reduce the band pass), so I decided to do some comparisons which i present below...

First off this morning I took a full disk in CaK using my regular favourite setup, this is a 40mm objective running at f10, with a 2x barlow after my CaK filter. I'm pretty happy with the outcome, it has lots of contrast, shows me proms and I get filaments now and then.

Imagecak-full-disk-40mm-f20 by Mark Townley, on Flickr

So next off, I tried my 100mm scope stepped down to 50mm aperture and running at a native f20 focal length. Expecting great things I was quite surprised when the outcome was a little washed in comparison with the image above.

Imagecak-full-disk-50mm-f20 by Mark Townley, on Flickr

Surprised, I still ran the same 50mm f20 configuration but this time with a 0.5x focal reducer on the nosepiece of the CCD

Imagecak-full-disk-50mm-f7 by Mark Townley, on Flickr

At this point I wondered if the filter itself was designed for f10 operation, as would be in the original CaK PST, so decided a full disk with the 100mm at f10, but with the 0.5x nosepiece on the camera to make the mosaic a bit more manageable...

ImageCaK-Full-Disk-100mm-f7 by Mark Townley, on Flickr

The contrast on this last disk is back a bit compared to the previous two. I'm certain the 0.5x reducer is throwing some spherical aberration into the mix to soften things up and lower the contrast a bit, but my conclusion here is that the filter in the CaK PST is optimised for a f10 beam. I can and have replicated the results of lower contrast by tilting the CaK elements in my filter stack. I'm certainly sticking with a native f10 running into it.

*Edit*

Just to throw confusion in, here is a disk taken in hazy skies with a 100mm f5 skywatcher refractor - this goes against convention and shouldn't work that well, but this disk isn't to bad, obviously taken on a different date than the above images...

Image100mm-cak by Mark Townley, on Flickr

Just shows how important the scope is to caK imaging... :?

The PDFs inserted further up this thread for the CaK filters used at the Paris Meudon indicate these were designed for a target wavelength slightly higher than 393.37nm wavelength so as when used in a non collimated beam would bring the target response of the filter down to 393.37nm.

Now, I wonder what focal ratio the Lunt CaK wedge was designed to work at to deliver a filter centred on 393.37nm?


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark

great results from that session. #1 seems to give really the best result


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Re: Lunt CaK module bandwide?

Post by marktownley »

Thanks Walter, I agree.

As a question aside - if a filter is designed to run at a higher target wavelength in a collimated beam so that when it used in a focused beam it is at the target wavelength, does this mean if it is used at a large f-number than it is intended (as in my 50mm f20 disk), does this mean that it would be operating at a wavelength on the red side of the target wavelength? Hope this makes sense!


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark

I'm very sorry. I don't believe that. I would guess if a filter is made for say f/10 it should even better work at f/15, but I have seen your results and I have to accept them as beeing true. However. I'll make my own measurement and comparison on the sun to confirm your findings. Hope it happens
Last edited by swisswalter on Sat Apr 26, 2014 6:25 am, edited 1 time in total.


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Re: Lunt CaK module bandwide?

Post by Valery »

Mark,

Your experiment is worth to read as an example of the enthusiasm of amateur astronomer who is trying to extract every bit of performance out of his available equipment. But from the scientific point of view this experiment is not perfectly objective.

See, some possible explanetions of the effect you observed:

1. 40mm F/10 objective + Barlow 2x incidentally deliver a perfect (or at least acceptable) SA correction at 393nm.
2. In the same time a 50mm F/10 (stopped 100mm F/10, right?) + reducer 0.5x(this is BIG reducing factor and this reducer is a simple achromat and has HORRIBLE HORRIBLE HORRIBLE level of SA at 393nm) deliver poor SA performance at 393nm and also poor field curvature (imminent with this reducer).

3. You are righ that possibly the PST CaK filter can be designed for longer wave length in a parallel beam (or quasi parallel) with the intention that at F/10 the most of aperture (edges!) will work at the CWL 393,37nm.

But we don't know and your experiment does not give us the answer. Possibly yes, possibly not. 50% on 50%.

I should note, that with my attempts to make sub nm CaK filter with steep curve I include in the calculations the CWL shift with converging beam (for F/10 aperture).


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Re: Lunt CaK module bandwide?

Post by marktownley »

Thanks Valery. Interestingly the 40mm f10 objective is one off a Ha PST, so maybe they used the same one for the CaK PST too? I don't know, would it be possible to design an objective that was corrected for SA at 656nm and 393nm?

The softness as a result of the SA of the 0.5x reducer I expected, but the one that caught me off guard was the fact that the 50mm f20 disk was distinctly lacking in contrast. I would have expected more contrast than I got.

All good fun!


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Re: Lunt CaK module bandwide?

Post by mdwmark »

Not one comment about my image,you guys are tough. That was shot with an old Astrovid (1/4" chip) with a Snappy type frame grabber. I am sure someone remembers them. There is no stacking, no processing like they do today. It was like shooting with film. You just go through the images till you find one that was good then save that one. And I shot it with an C-8! I don't remember to many K-line images with that scope. For Ha they do work pretty good for solar. In the 90's to the mid 2000's the SCT's where the most common scope for solar.

Mark, with the 100mm you may need to tilt the filters to move it better on band or it maybe, like I said about the AR's not transmitting well at that wavelength. Either would lower the contrast.

Mark Wagner


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Re: Lunt CaK module bandwide?

Post by marktownley »

You make me feel bad now for lack of comment on your image :oops: The process of imaging today is definitely a bit different than then!

I think i'm going to keep my filters 'still' and stick with native f10 imaging, taken me ages to work out a configuration that controls the reflections / ghosts.


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Re: Lunt CaK module bandwide?

Post by solarchat »

well, to be fair, you did post your image in someone else's post, and in the commercial solar filters/hardware section.
I am sure it would have gotten more comments in its own thread in the main forum...:)
I have over 20,000 videos on youtube of the Sun through some of the nicest equipment known to man and have over 5000 images of outreach events posted on this forum. I used to get a little resentful because no one really gives a crap about outreach in this hobby, or the Sun at all in the general public , but then I decided that I was doing what I was doing for myself and the students I see. There is no way I can compete with Justin Bieber and that's that...

I get the same three comments from the same three people on every post, and I treasure them each and every time...:)
Keep up the good work man and don't let the number of comments affect you one bit. I can assure you that I and many others like Walter and Mark read every single post on here if it makes any difference.


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark W

Now I'm feeling also a little bit bad. You posted a pic and an information. The pic was nothing special to me, because I did not know the background of it (taken years ago). I did very well give a comment to your Information though. I suggest we stay friends and go on.

Although Mark T. is very well a head of the CaK race, I'm not giving up (please note, we know each other and there is a sort of deep friendship. We will fight about every Cent and angstrom, but with the only target that we get closer to the goal


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Re: Lunt CaK module bandwide?

Post by marktownley »

Interestingly I was looking through the 'archives' on my website and is 3 years since i made my first CaK filter http://brierleyhillsolar.blogspot.co.uk ... april.html - a single stack version at that stage, and I was already pontificating as to the bandwidth. I was using the 70mm f6 at that point so was never going to be getting as much out of the filter as I could...


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Mark

yes your current work has lightways improved, however, for 2011 that was still not a bad pic, congratulations , I know 3 years late ;-)


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Re: Lunt CaK module bandwide?

Post by mdwmark »

Hi Guys, You know I was kidding, about no comments. What I was trying to show is with K-line it doesn't need to be a high end scope to get good results.
What I like about this site is, if someone gets to high and mighty there is someone in this group that can put them back in place.
Getting back to the bandwidth. The 2-3 Ang range is a good place to be. It show the plage well. But it does make a difference if you are not centered on the line. The contrast will be lower. The other thing that will lower the contrast is how blue the sky is. If only a little of blue is getting through then the contrast will be lower.
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Re: Lunt CaK module bandwide?

Post by Wah »

Is there anyone here know why manufactures choose to produce CaK filter rather than CaH filter?
In my SHG images, I find the H line is always a bit brighter than K line.


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Wah

that I do not know, but out of experience my Ca II H filter is not as contrasty as the CaK filter. So it makes more fun to Image in the K line rather than the H line


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Re: Lunt CaK module bandwide?

Post by Wah »

Hi swisswalter, where did you get those Ca-H/K solar filters?
Are they the same bandwidth? :roll:


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Re: Lunt CaK module bandwide?

Post by mdwmark »

The K-line is a little broader. From the book, Solar Spectrum 2935Ang to 8770Ang by Rowland's preliminary tables. They have the width (full width) of K-line at 20.2 ang. and H-line at 15.4ang.
From a manufacturing point, it does matter which one you pick. You just need the correct blocker for the wave length you want. It is not unusual to have a peak at the K-line and one on the H-line with the same etalon. The K-line is just more commonly ordered.
The professional observatory tend to do study's using the K-line. I will check into it why K over H.
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Re: Lunt CaK module bandwide?

Post by swisswalter »

Wah wrote:Hi swisswalter, where did you get those Ca-H/K solar filters?
Are they the same bandwidth? :roll:

Hi Wah

the Ca II H is from Daystar, the CaK from Lunt


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Re: Lunt CaK module bandwide?

Post by astrodanco »

I have over 20,000 videos on youtube of the Sun through some of the nicest equipment known to man and have over 5000 images of outreach events posted on this forum. I used to get a little resentful because no one really gives a crap about outreach in this hobby, or the Sun at all in the general public , but then I decided that I was doing what I was doing for myself and the students I see. There is no way I can compete with Justin Bieber and that's that...
And if Stephen feels that way, imagine how the rest of us mere mortals feel. :cry:


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Re: Lunt CaK module bandwide?

Post by Merlin66 »

Hale's original spectroheliograph was used to study the CaK lines and it has become the defacto standard.

Zirin "Astrophysics of the sun", p155-168 says of the CaK line "Because the central emission core of the K line is so strong, we can identify K-line spectra with corresponding magnetic features" He then goes on to enounce the "The (6) K line rules"......


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Hi Ken

thank you very much for that information


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Re: Lunt CaK module bandwide?

Post by Wah »

swisswalter wrote: Hi Wah

the Ca II H is from Daystar, the CaK from Lunt
Do both filters have the same bandwidth? Maybe the bandwidth affects the contrast more than the "H-K line comparison"?


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Re: Lunt CaK module bandwide?

Post by swisswalter »

Wah wrote:
swisswalter wrote: Hi Wah

the Ca II H is from Daystar, the CaK from Lunt
Do both filters have the same bandwidth? Maybe the bandwidth affects the contrast more than the "H-K line comparison"?
hi Wah

thank you very much. That is a good point. The CaK is around 2,4 A and the Ca II H around 5 A


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Re: Lunt CaK module bandwide?

Post by thesmiths »

In my preliminary SHG study of Calcium, at the same bandwidth, the H and K images looked the same. Of course, my resolution was not very high. But quantitatively, I did not see any difference. So I also wonder why the typical choice of K over H.


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