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Coronado SolarMax II "Double Stack" Etalon?

solar astrophotography imaging accessories
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#1 Lost in Space

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Posted 20 October 2020 - 05:08 PM

I am confused about the Coronado SolarMax II 60mm Ha Etalons which are being sold with the description that they are for Double Stacking.  I have read a caution by Meade/Coronado that the separately purchased Double Stack (DS) etalon is not to be used as a "standalone filter."  

 

Does that mean that a DS etalon is manufactured to different specifications than a Primary etalon, or are they both built the same?

 

I am wondering if the DS etalon is lacking safe filtering which a Primary etalon would have, in order to minimize the loss of Ha light to the Primary etalon?  --  OR is the stated caution simply indicating that a DS etalon cannot be used without the appropriate blocking / ITF filter (BF10, BF15, etc.) as would always be required usage with a regular Primary etalon?

 

I have not been able to get any answers by Googling this, and Meade's telephone customer service cannot be reached by phone due to COVID.  And for that matter, I have seen a comment that Meade CS is not very familiar with the Solar product line, so would an answer from them even be correct?

 

I am hoping one or more of the experienced and knowledgeable Solar experts here can enlighten me.

 

Many thanks!



#2 germana1

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Posted 20 October 2020 - 05:49 PM

The double stack filter can be used with a refractor with the blocking diagonal, or added to the primary .

say for example I have a TV 102 the 90mm filter screws right on the front of the scope but the blocking diagonal must be used, the 

filters are the same 



#3 hopskipson

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Posted 20 October 2020 - 06:11 PM

The double stack filter can be used with a refractor with the blocking diagonal, or added to the primary .

say for example I have a TV 102 the 90mm filter screws right on the front of the scope but the blocking diagonal must be used, the 

filters are the same 

That is correct!  I'm using a 90mm DS etalon with a Lunt blocking filter on an ES 102 ED.  I had an adapter made to fit the objective.  I got another DS etalon to DS the scope.



#4 Lost in Space

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Posted 20 October 2020 - 06:28 PM

The double stack filter can be used with a refractor with the blocking diagonal, or added to the primary .

say for example I have a TV 102 the 90mm filter screws right on the front of the scope but the blocking diagonal must be used, the 

filters are the same 

 

That is correct!  I'm using a 90mm DS etalon with a Lunt blocking filter on an ES 102 ED.  I had an adapter made to fit the objective.  I got another DS etalon to DS the scope.

 

Thanks, germana1 and hopskipson, I have actually held a DS etalon and gave it a good look-over, and did not notice any differences on the outside, but did not know what was going on inside.

 

I am guessing Meade doesn't want anyone to buy this standalone etalon and expect to use it without a BF.  That would be a disaster for the person involved, and an almost certain lawsuit against Meade.  Quite frankly, I am surprised they have not expressed the BF requirement more clearly, unless they feel they can sell more Primary etalons this way.



#5 ron scarboro

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Posted 21 October 2020 - 01:49 PM

I am guessing Meade doesn't want anyone to buy this standalone etalon and expect to use it without a BF.  That would be a disaster for the person involved, and an almost certain lawsuit against Meade.  Quite frankly, I am surprised they have not expressed the BF requirement more clearly, unless they feel they can sell more Primary etalons this way.

You hit it on the head.  A filter for DS doesn't have a blocking filter in the package.  No other differences.


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#6 BYoesle

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Posted 22 October 2020 - 08:26 AM

 

A filter for DS doesn't have a blocking filter in the package.  No other differences.

 

True in general, but there can be subtle differences between etalons. I have noted that a good deal of DS etalons have a CWL that is tuned a little (to a lot) higher so that theoretically they come on band with a bit more of tilt to make secondary ghost images easier to remove from the field of view. If they have it, the rich-view tuning* can be applied to bring these etalons back on band. Sometimes, however, they require too much tilt, and therefore would make poor primary etalons compared to those that don't need as much tilt.

 

* Rich-view tuning can be uneven if too much is required to compensate for excessive tilt.

 

Unfortunately, it will be impossible to tell about this without actually having the etalon in use.


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#7 Lost in Space

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Posted 22 October 2020 - 10:58 AM

True in general, but there can be subtle differences between etalons. I have noted that a good deal of DS etalons have a CWL that is tuned a little (to a lot) higher so that theoretically they come on band with a bit more of tilt to make secondary ghost images easier to remove from the field of view. If they have it, the rich-view tuning* can be applied to bring these etalons back on band. Sometimes, however, they require too much tilt, and therefore would make poor primary etalons compared to those that don't need as much tilt.

 

* Rich-view tuning can be uneven if too much is required to compensate for excessive tilt.

 

Unfortunately, it will be impossible to tell about this without actually having the etalon in use.

Hi Bob!

 

I am wondering if etalons sold as Primary etalons would be completely exempt from this issue, but I imagine there is a range of quality that a Primary must fit within.

 

Based on your comments about DS etalons, I would think that two Primaries doublestacked together might be better than a Primary doublestacked with an etalon sold as a DS etalon.  Or is that opening up greater chances for secondary ghost images with two Primaries?

 

But as you mentioned, I guess you would have to test them (assuming you have multiple etalons to play with) to see which two work together the best.

 

By the way, what is a "CWL?"  I'm not familiar with that term.  And, would you explain how a Rich-View Tuner works in conjunction with the Tilt Tuner?  That has me puzzled, for DS or SS viewing.  confused1.gif  undecided.gif  thinking1.gif



#8 BYoesle

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Posted 22 October 2020 - 11:52 AM

Hi Ed,

 

CWL refers to the etalon's central wavelength. No two etalons are identical. And for front mounted etalons the CWL is generally a function of the spacer thickness. These are ideally made so that the CWL is just slightly above the H alpha emission, so that only a little tilting will bring the filter "on-band." In the early Coronado filter days, only single front etalons were available to double stack with, and if you had two, the one that used the least tilt to get on-band was the primary etalon. The second etalon that needed more tilt was the secondary, since the added tilt helped to remove the reflective ghost images while keeping the filter closely on-band.

 

Later, secondary double stacking etalons were made with the CWL deliberately a bit higher to allow for the tilting needed to remove ghost reflections. Since tilting blue-shifts the CWL, it was hoped that this would then lead to the etalon being on-band when tilted. Unfortunately, some of the etalons I have encountered require too much tilt to come on-band, and these are inferior by producing greater contrast non-uniformity, which is called banding. Making the etalon spacers the correct thickness to be near on-band is almost as difficult as making the etalons themselves. Therefore relaxing the tolerance of the spacer thickness can be corrected to a degree via air or mechanical pressure tuning.

 

The tiltable rich-view etalons work by allowing one to tilt the etalon to remove the ghost reflections, and then add mechanical pressure to the etalon plates to blue shift the etalon back on-band. In my experience some of these still require too much tilt (to high a CWL) and even with additional rich-view compression tuning the contrast is not as uniform as it could be. For the current Coronado etalons, I'm not sure if they distinguish a primary versus secondary double stacking etalon - they may all be within a certain spacer tolerance - but it may be a greater degree of tolerance which might lead to greater variability of performance.


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#9 Lost in Space

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Posted 22 October 2020 - 06:14 PM

Hi Ed,

 

CWL refers to the etalon's central wavelength. No two etalons are identical. And for front mounted etalons the CWL is generally a function of the spacer thickness. These are ideally made so that the CWL is just slightly above the H alpha emission, so that only a little tilting will bring the filter "on-band." In the early Coronado filter days, only single front etalons were available to double stack with, and if you had two, the one that used the least tilt to get on-band was the primary etalon. The second etalon that needed more tilt was the secondary, since the added tilt helped to remove the reflective ghost images while keeping the filter closely on-band.

 

Later, secondary double stacking etalons were made with the CWL deliberately a bit higher to allow for the tilting needed to remove ghost reflections. Since tilting blue-shifts the CWL, it was hoped that this would then lead to the etalon being on-band when tilted. Unfortunately, some of the etalons I have encountered require too much tilt to come on-band, and these are inferior by producing greater contrast non-uniformity, which is called banding. Making the etalon spacers the correct thickness to be near on-band is almost as difficult as making the etalons themselves. Therefore relaxing the tolerance of the spacer thickness can be corrected to a degree via air or mechanical pressure tuning.

 

The tiltable rich-view etalons work by allowing one to tilt the etalon to remove the ghost reflections, and then add mechanical pressure to the etalon plates to blue shift the etalon back on-band. In my experience some of these still require too much tilt (to high a CWL) and even with additional rich-view compression tuning the contrast is not as uniform as it could be. For the current Coronado etalons, I'm not sure if they distinguish a primary versus secondary double stacking etalon - they may all be within a certain spacer tolerance - but it may be a greater degree of tolerance which might lead to greater variability of performance.

Thanks Bob!  You are a tremendous asset to this forum, and I appreciate your generosity in sharing your knowledge and experience with us!



#10 hopskipson

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Posted 22 October 2020 - 07:27 PM

Hi Ed,

 

CWL refers to the etalon's central wavelength. No two etalons are identical. And for front mounted etalons the CWL is generally a function of the spacer thickness. These are ideally made so that the CWL is just slightly above the H alpha emission, so that only a little tilting will bring the filter "on-band." In the early Coronado filter days, only single front etalons were available to double stack with, and if you had two, the one that used the least tilt to get on-band was the primary etalon. The second etalon that needed more tilt was the secondary, since the added tilt helped to remove the reflective ghost images while keeping the filter closely on-band.

 

Later, secondary double stacking etalons were made with the CWL deliberately a bit higher to allow for the tilting needed to remove ghost reflections. Since tilting blue-shifts the CWL, it was hoped that this would then lead to the etalon being on-band when tilted. Unfortunately, some of the etalons I have encountered require too much tilt to come on-band, and these are inferior by producing greater contrast non-uniformity, which is called banding. Making the etalon spacers the correct thickness to be near on-band is almost as difficult as making the etalons themselves. Therefore relaxing the tolerance of the spacer thickness can be corrected to a degree via air or mechanical pressure tuning.

 

The tiltable rich-view etalons work by allowing one to tilt the etalon to remove the ghost reflections, and then add mechanical pressure to the etalon plates to blue shift the etalon back on-band. In my experience some of these still require too much tilt (to high a CWL) and even with additional rich-view compression tuning the contrast is not as uniform as it could be. For the current Coronado etalons, I'm not sure if they distinguish a primary versus secondary double stacking etalon - they may all be within a certain spacer tolerance - but it may be a greater degree of tolerance which might lead to greater variability of performance.

I'm glad you cleared this up.  I have 2 DS Richview tunable SMII etalons that I use on a 102 mm ED scope.  I do my best with my limited schedule/weather viewing time.  What I usually do is start with one etalon with minimal if not 0 tilt ant then Richview tune to get the most details.  Then add the second etalon, tilt to get the ghost image and then Richview to get the best results.  If time allows I try to "clock" the etalons to see if I can improve the view.  This always takes a bit of time and since family free time is a premium I have to settle for what I get and enjoy the view.




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