A surprise in the LUNT CaK wedge

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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi CaK freaks


just arrived home and took a pair of 395 nm chinese filters out of my mail box. I have mounted them already and we expect sunshine on wendsday :woohoo:

Looking at a light bulb they show a nice violett, but I guess they are much to broad. We will see, hopefully soon.


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi all

another hope is gone :( the chineese 395/30 filters are too broad, also in the case of a stack

the plot overview








the plot close up






the real result on the sun





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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

:(

Thanks for trying Walter...


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Mark

don't be disappointed. The search goes on. The show must go on ;-)


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Re: A surprise in the LUNT CaK wedge

Post by Valery »

swisswalter wrote: The search goes on. The show must go on ;-)
I read the thread with a greet interest. Thanks to all who have participated.

But the question what is the end of story?


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Valery


now, the show goes on, we just look out for the acteurs ;-)


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

We need someone who can manufacture these CaK filters economically to the 2.2a bandpass - Aries? ;)


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Re: A surprise in the LUNT CaK wedge

Post by Valery »

marktownley wrote:We need someone who can manufacture these CaK filters economically to the 2.2a bandpass - Aries? ;)
No, not at this moment and nearest future. :)

But what with Andor 390 + 393( ? ) filters combo? As I saw the pictures, they are nearly as good as with Lunt wedge and brighter.


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Valery

thank you very much. Yes you are right, the combo 390+393 is much brighter than the Lunt piece but not narrow enough


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Colin has the best idea I seen for a while. Perhaps a mica inserted in between the 10nm filters will tell if it is a small etalon. Colin Will calcite work as good as mica? How much is a suitable piece of mica? Can we find a source?


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

WHOOOA! Cheap man! Ordering some now!

https://www.google.com/shopping/product ... N4BEKYrMAY


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

yes, Mica is indeed cheap. $$$'s are not the problem. Cleaving one single thin error free sheet out of it is one of the challanges. ;)


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

I personally don't think just inserting a piece of mica between 2 filters like this will work at all - too many variables: Firstly we don't know if stacking 2 filters like this is effective, secondly we don't know the exact gap needed between the 2 filters if it did work, and it would have to be an precise gap. Thirdly, like Walter says there is no effective way for us to effectively cleave one single error free sheet at the right thickness (which we don't know).

By all means try it Joe, but Walter did some considerable trialing with the mica and trying to make spacers to repair a Lunt 50 etalon, with no proper success, and this is with Walter having access to facilities in a professional chemistry lab...


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Mark - Just to be devils advocate, I am going to disagree as Colin has pointed us this direction and mark Wagner has mentioned it in the past. I PMd Mark W over at the CN thread to come over and give us some input on the idea. Perhaps on mica thickness, filter stack configuration, quality of cleave and expectations on cut. I hope he engages us. He seems to be the man with the most experience on the mica issue.

Mark W are you there?


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

Devils advocate is good! :)


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

:lol: Just feel I gotta, Mini etalon is an intriuging idea and I am very curious to see what it will take to create such device. Provding it is doable. I know Mark has posted stack sequences before but I don't recall us focusing specificaly on a mica eatalon in our stacks. Could be a interesting discussion. :)


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

I like that thread and "devils advocat" is a great term. They use to be very, very insistent, which is not very easy to scope with all the time. :)

Joe are you thinking of spacing two filters with a mica sheet or are you thinking of attaching two reflecting filters with a mica piece (daystar type) :?:

I'm happy to send you some MICA from Africa if the interest is great, at no cost :)

an example

MICA-Lump.JPG
MICA-Lump.JPG (487.76 KiB) Viewed 4018 times


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Hallo Walter, sorry for not getting back sooner - been a busy day. The question you ask is a good one. I am interested to see what Mark Wagner says. I have thought about both methods but not yet decided. You mentioned "attaching", attaching perhaps the way Lunt seems to have done? Yes. something similar. I have yet to go back and look at some of the information Mark W gave us earlier about how he constructed some of his etalons and filter stacks.

I remember in one thread we were engaged with Catlin on constructing the double pass filter that required a binding of two prisms with an optical contact agent that had a nome like Canada balm or something termed similar to this. Can you remember the name? I was wondering if that is what we are seeing on your micro side view of the Lunt. I am Wondering if that is a method? Or is mica spaced or optically contacted some other way?

Can two reflecting cavity type filters be bound either side of mica and achieve the band cut based on bifrigence alone or will there have to be BG or other type of glass spacing? Will there have to be a gap? or will the natural bifringence do the job if simply contacted or pressed to the mica mechanically?.

Or will there have to be reflective a cavity filter, a spacer, mica and then some type of blocker like a 390 series , 410 or other behind the mica? I reallly have to go back and read Marks previous posts. When my hard drive crashed i lost the links to those posts and the favorites I had saved in the old form did not follow me here. Thus I must dig through the old posts to find some of Marks Ws stack configurations. Do you have the links to those posts saved? If so can you relink me? Regardless, as I remember it we still did no speak specifically to optically binding mica, only polished crystal or glass etalons. So as you can see I have many questions on how exactly to approach the stack.

Best Regards,

Devils Advocate :seesaw
Last edited by sullij1 on Fri Feb 28, 2014 3:51 am, edited 2 times in total.


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Also, thank you for your wonderful offer to share your mica stash but I already have several packages being shipped as we write. :bow2


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Re: A surprise in the LUNT CaK wedge

Post by Peter Williams »

Canada Balsam is used as a cement when mounting microscope slides and cover glasses.
http://en.wikipedia.org/wiki/Canada_balsam
Also has good optical properties and used to cement lens elements together. Sounds like what you are referring to.


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Thank you Peter. Welcome to the nerdy conversations! :D


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Ah Ha, I found the old conversation but it only brings up more questions. i wonder if Mark W will share some new speculations after seeing the microscope view of the lunt magic back filter?

Here are the important parts of his previous post regarding etalon and stacking designs. But this makes me want to ask :

What was used as the "ITF" in this design?

What was the whole title of the "10 angstrom blocker" filter? that is "way" tight (narrow)! Where did they come from (source)? Did he mean 10nm CaK line type?

Or what was the bandpass on the 10 angstrom if the FWHM was 10angstrom?

Was this stack optically bonded as etalons are by letting the vacuum naturally form?

How is this accomplished with mica?

He stated "UV Polaroid when "thickness of the mica was not a ½ wave plate". What does this mean thickness is 1/2 wave plate mean? I thought wave value was measured on the flat surface not the thickness.

How is it measured?

MOSTLY - Not so much interested in the etalon design I think the "Paragraph 6 design" is very close to where we want to be.


FROM HIS PREVIOUS POST:

6) The difference in design of the two. The Daystar has two different K-line housing. The standard tiltable K-line is nothing more than two 10Ang blockers and an ITF. So it went AR, 10ang, BG25, ITF, 10ang, BG25, AR. Del would call this a 5ang filter but it was really not. But it does work, the plage was there and you could see prominence sometimes.
The etalon based filter was the other design. At K-line it takes much more temperature to move the bandpass. So unlike Ha the temperature control is less critical. The other advantage is the bandpass are broader so tilting can be use easier. I did put some etalon filters in the tiltable housing but added a strip heater and temperature controller to have more control of the bandpass.

Ok, the design for the etalon based filter would be AR, 10ang,(sometime BG25 and UV Polaroid )etalon, ITF, BG25,AR. You would need to use the UV Polaroid when the thickness of the mica was not a ½ wave plate or the next peak was not outside the blocker. This is because the mica is birefringent and will have two peaks. One for the different indexes on the different axis.
It should be noted that the UV Polaroid material we used is no longer made. So the ones I make need to be ½ wave plates to keep the HW as narrow as possible.

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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

And one last question: If we are introducing a bifringment (mica) are we back to a tilting mechanism to hit - widen and narrow the passband?

Nite Nite! :lol:


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

thank you very much for all the questions, I'm not in a position to answer them. But maybe we can discuss one thing after the other.

As I understood the 1/2 wafe plate means if you want to make a solid CaK filter stack the mica has to have a thickness of ~200 nm. In the case of a Ha solid etalon ~330 nm. I'm sure the mica is optically bound to the glass plates and there is no glue what so ever. The edges of the stack might be coated in order die protect the coatings of the glass plates from humidity and corrosion of the silver coating. personally I do not see me in a position to handle a 200 nm thin plate, you know how thin that is, just a fifth of a micron :oops:


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Interesting Walter. Now I really want to see Mark Ws input on that.


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

I'm looking forward to the input of Mark too


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Got an email from Mark, he is having trouble with the login on the new site. I recommend he re-register. He will be with us when he gets it sorted out.

Best


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

I've ordered a couple of pieces of BG25 to put into my CaK stack, see if they will help with the reflections...


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Got the mica today. Been buried in my optics book looking at the definitions for 1/2 wave mica. Hecht Optics, second edition, 1987. I get it now. Minimum thickness for a mica 1/2 wave plate is 60 microns. The mica I received is extremely clear and will easily cleave naturally ~ that thickness in large sheets. Now to break out the micrometer.

(This was with sodium light.) Edit 03/03/2014
Last edited by sullij1 on Sun Mar 09, 2014 4:36 pm, edited 1 time in total.


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

@ Mark W. - So the mica will be used as the polarizer ?


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Need to order the BG25. @ Mark T. - Can you post your source for me?


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Here is the mica, the paragraph on 1/2 wave thickness is visible in the book:

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Mica and Book by Sullij1, on Flickr

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Mica close jpg by Sullij1, on Flickr


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

very fine chunks of rock


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Re: A surprise in the LUNT CaK wedge

Post by solarchat »

Sulli,

Im gonna need you to pick up the pace on this project. I need a 300mm .4A etalon by the end of March if you don't mind.


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Re: A surprise in the LUNT CaK wedge

Post by Valery »

Can somebody tell me which is better for CaK photography - a modified CaK PST (with 2,2A filter) or a LUNT CaK wedge?
Which one deliver more contrast, more detailed and more bright image?

Thanks.

Valery.


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

sullij1 wrote:Need to order the BG25. @ Mark T. - Can you post your source for me?
I got mine from Knight Optical here in the UK, Two 25mm diameter pieces including postage were £40 ($60). Cheapest way would be for you to buy it stateside - just google Schott BG25...


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

solarchat wrote:Sulli,

Im gonna need you to pick up the pace on this project. I need a 300mm .4A etalon by the end of March if you don't mind.
We can easily and safely make the CaK modules work imaging wise (not visual) in scopes up to 300mm - assuming fracs. 0.4a may take us a few more days, but down to 1.5a we can do now. My laser cutter at work has been busy this week making me some new parts that should allow me to tighten up the 1.5a a bit more too. My personal mission with CaK is filaments and proms, i've just about got the proms sorted, filaments are more intermittent. However the thing I like about all these solar imaging systems is that its all governed by physics and so by manipulating variables and with a bit of engineering we can get to where we want to be ;) I love the 'puzzle' it all presents :seesaw


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

Valery wrote:Can somebody tell me which is better for CaK photography - a modified CaK PST (with 2,2A filter) or a LUNT CaK wedge?
Which one deliver more contrast, more detailed and more bright image?

Thanks.

Valery.
Difficult question. I think the biggest thing with CaK is the refractor it is used with in terms of the spherical aberration (which you have a very clear knowledge of Valery). The other factor with imaging is the scale it is being photographed at and the size of the pixels on the chip: Lots of people who are getting less than ideal results at 393nm imaging wise - in my opinion, are just under sampling the image, in some cases quite significantly resulting is a big loss of detail.


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Re: A surprise in the LUNT CaK wedge

Post by Valery »

marktownley wrote:
Valery wrote:Can somebody tell me which is better for CaK photography - a modified CaK PST (with 2,2A filter) or a LUNT CaK wedge?
Which one deliver more contrast, more detailed and more bright image?

Thanks.

Valery.
Difficult question. I think the biggest thing with CaK is the refractor it is used with in terms of the spherical aberration (which you have a very clear knowledge of Valery). The other factor with imaging is the scale it is being photographed at and the size of the pixels on the chip: Lots of people who are getting less than ideal results at 393nm imaging wise - in my opinion, are just under sampling the image, in some cases quite significantly resulting is a big loss of detail.
Mark, thanks. But this is not what I hoped to hear. Lets speak of identical telescope (refractor corrected for 393nm) in both cases, enough sampling, same camera.
So, which is the best of two?

Valery.


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Re: A surprise in the LUNT CaK wedge

Post by marktownley »

I have not compared both directly side by side, but I would say the Coronado filters as optically they are simpler and so, I think, will offer better contrast...


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

solarchat wrote:Sulli,

Im gonna need you to pick up the pace on this project. I need a 300mm .4A etalon by the end of March if you don't mind.
:lol: You heard the man, SloarChat CaK engineers - GIDDY UP!!!!!! Times a wasten! :lol: Where is that Wagner guy! ;)


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Valery wrote:
marktownley wrote:
Valery wrote:Can somebody tell me which is better for CaK photography - a modified CaK PST (with 2,2A filter) or a LUNT CaK wedge?
Which one deliver more contrast, more detailed and more bright image?

Thanks.

Valery.
Difficult question. I think the biggest thing with CaK is the refractor it is used with in terms of the spherical aberration (which you have a very clear knowledge of Valery). The other factor with imaging is the scale it is being photographed at and the size of the pixels on the chip: Lots of people who are getting less than ideal results at 393nm imaging wise - in my opinion, are just under sampling the image, in some cases quite significantly resulting is a big loss of detail.
Mark, thanks. But this is not what I hoped to hear. Lets speak of identical telescope (refractor corrected for 393nm) in both cases, enough sampling, same camera.
So, which is the best of two?

Valery.
Valery, that's one of the things we are trying to sort out. Nothing will be conclusive until we start getting images from each device in order to make the determination you are asking for. Currently, Marks device is performing better.


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Mark, thanks. Will take a look around.


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

solarchat wrote:Sulli,

Im gonna need you to pick up the pace on this project. I need a 300mm .4A etalon by the end of March if you don't mind.

:lol: :lol: :lol: :lol: :lol: :lol: :lol:


I guess the CaK filter is a tad better then the LUNT double plate. Stacking both will reveal the best result so far. Stephen we nedd only that Little plate from you Coronado CaK gun and we can Show you ;)


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Ah, another question answered as far as bonding to the mica. I see the mica itself is coated in the daystar elements. But perhaps stacking will get us there. here is a link to a description on how daystar mica is selected and coated. it is in the text about midway through.

http://www.scsastro.co.uk/userfiles/fil ... Filter.pdf


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

thanks for the white paper


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

If ya care... How to cleave mica.

http://www.youtube.com/watch?v=oXyPhBtMNqE

Perhaps a higher grad mica I will buy said Yoda. :)

http://www.2spi.com/catalog/submat/mica-disk.php

Other cleaving methods:

http://cr4.globalspec.com/thread/26982/ ... ca-methods


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Re: A surprise in the LUNT CaK wedge

Post by swisswalter »

Hi Joe

thanks for digging that out


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Re: A surprise in the LUNT CaK wedge

Post by Peter Williams »

sullij1 wrote:...here is a link to a description on how daystar mica is selected and coated. it is in the text about midway through.
http://www.scsastro.co.uk/userfiles/fil ... Filter.pdf
Fascinating stuff, it's helping me to understand more about how these etalons and filters are made and how they work.
Thanks.


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Re: A surprise in the LUNT CaK wedge

Post by sullij1 »

Ok, had my nose in the books trying to calculate a ½ wave mica at 393.4 nm. Doing this until Mark W. can get in and shed more light on the 10 angstrom filters and the ITF for the CaK.

My attempt will be at forming an etalon using the OmegaBob pair.

So the calculation for a ½ wave plate using a bifringent (mica) is this:

T = ____Y_____
2(ue – uo)

Where:
T= thickness
Y= wavelength in meters (angstrom)
ue and uo = the bifringent indexes for mica

So:

Y= 3934e-10
ue and uo= (1.596 - 1.63) (Fixed this in edit, sorry too many beers when copying math over. :))

So:

T = ____3934 e-10_____
2 (1.596 – 1.63)

T= ____3934 e-10_____
0.068

T = 2.185555 e-5 meters

Convert to micrometers

T = 21.85 micrometers for a ½ wave mica plate at 393.4 nm passband

Please feel free to check my math and comment. Light Machinery wave plate calculator places the thickness at 20.5 micrometers for a quartz ½ wave plate where the refractive index for quartz is near mica. Mica averages to a refractive index of ~1.6 and quartz is 1.458. so close enough for me. :D

~20 micrometers may be doable cleave on the mica. (I have been practicing.) As Mark W. mentioned if I can’t make the 20 um cleave, a polarizer will fix the thickness issue. (this may also indicate that a very flat etalon can be constructed using dichroic multilayer deposition. As in Walters side on picture.)

Online reference for calculation if you want to do it (just change the target wavelength to CaK instead of sodium light):

http://books.google.com/books?id=vdXHcu ... te&f=false

Now for the weird part – I am going to make a bunch of assumptions based on the OmegaBob CaK pair to form an etalon. Assumptions:

1) Bobs pair will form an etalon if spaced properly behind the wave plate and the finesse is right.
2) Bob has his pair properly polarized
3) Bobs pair will form the single cavity reflectance and transmission when spaced properly.

I don’t completely understand the Light Machinery etalon calculator but based on the Cak wavelength parameters I punched into the calculator, with a 1mm air spacing, It looks to land a 0.02 angstrom passband. Clearly I have done something wrong but - it is a go at it.

Colin K or Mark W, Mark T, Walter or anybody who knows, please feel free to correct all my errors where you see them. I am on the learning curve. And I don’t take it personally.

Here is screen print of the LM calcs:

I should have probably made it a 1st order wave plate but changing order and retardation tolerance made no difference in thickness to the wave plate.

Image
WAVEPLATE by Sullij1, on Flickr

Feel free to correct anything here:

Image
ETALON LM by Sullij1, on Flickr

There ya go. Fire away! :D

In the mean time I will attempt to construct the filter stack. Will probably take me a week before I am ready to test. You can save me time by making corrections now.
Last edited by sullij1 on Sun Mar 09, 2014 4:39 pm, edited 2 times in total.


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