Measurement of a Quark Ha filter with Sol'Ex spectrometer

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Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

Hello,

I've been spending some time on the measurement of the FWHM of a Quark Ha filter with Sol'Ex spectrometer.

The method is straightforward. The Quark is mounted with its 4.3x telecentric at the focus of the C8 EdgeHD. So we have a f/45 telecentric beam falling on the Quark. The spectrum of the Sun is taken with/without the Quark (with the Sol'Ex spectrometer).
The transmission profile of the filter is given by the division : spectrum with Quark / spectrum without Quark.

I measured the transmission profile at different temperatures to check for consistency in the results.

For example, here we have four succesive images:
- the solar spectrum,
- the solar spectrum transmitted by the Quark at ambiant temperature,
- the solar spectrum transmitted by the Quark set to Ha (about 55°C).
- same as above to show the secondary peaks of transmission of the etalon (for FSR measurement).

http://astrosurf.com/viladrich/astro/in ... ectres.jpg

Then, we have the associated transmission profile with measured FWHM and bandwidth at 10% peak transmissson :

http://astrosurf.com/viladrich/astro/in ... ned-Ha.jpg

http://astrosurf.com/viladrich/astro/in ... mbiant.jpg

As you can see the measures are very consistent (this is the same with other measures not presented here). The bandwidth at 10% is 3x the FWHM, identifcal to the theoritical value.

FWHM given here are measured directly on the graph. Another way to do it is to curve fit the profiles with a Lorentzian curve (which is the theoritical profile of a Fabry-Perot etalon). The resulting FWHM are 1.05 A and 0.95 A. This is very close to the values derived directly from the graph.

The Sol'Ex version used is an "improved" one with a 125 mm collimator (instead of 80 mm) to improve spectral resolution.

All in all, I would say the FWHM of this Quark is 1.0 A (+/-0.1 A).

The use of the solar spectrum for the measure means there is hardly any room for error. You can even make your own estimation based on the spectrum images given here.

An important point is that the part of the filter sampled is 10 micron x 4.5 mm, so possible non uniformity of the filter are not considered in the measure.

Some more info here :
http://astrosurf.com/viladrich/astro/in ... ark-1.html


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by Dennis »

Thats interesting, thanks for sharing Christian.
Was it a Prominence version of the Quark?


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

Hello Denis,
No, it was the chromosphere version. I forgot to mention.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by MalVeauX »

Great info Christian, thanks; very interested to try this with my etalons to see where they fall on things.

Very best,


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by Bob Yoesle »

Very interesting results Christian!

It seems either you have gotten an "out-of-spec" Quark filter from DayStar, or they are misrepresenting the actual quality of the Quark:

"Each Quark is warranted to have a FWHM bandpass (when introduced into a focal plane beam of ~F7-F/9) of 0.25 - 0.5."

Perhaps the secondary mirror amplification of field angles (similar to a 5 X Barlow lens) or the HD optics does not allow the 4.2 Quark telecentric lens to perform optimally, thereby broadening the FWHM? On the other hand, the Baader telecentrics and I assume the AiryLab telecentric do not affect FWHM broadening? Or would the HD optics make a difference? I note the Triband telescopes are non-HD versions of the base SCTs.

It might be interesting too see what differences - if any - might result from a measurement via an f10 refractor objective, and a non-HD SCT, on the FWHM.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

Hi Bob,
I understand DayStar statement as :
"in a f/7 to f/9 beam, the 4.3 x telecentric turns the beam into a f/30 to f/38.7 telecentric beam"
=> this part of the story is true, but the second part of the story is very doubtfull. Indeed, even a 0.3 A mica-spaced etalon will have an effective FWHM of 0.48 A at f/30, and 0.38 A at f/38.
So, if the statement of DayStar was true, it would mean that these etalons were at 0.3 A (or better) in collimated beam.

Here is a graph you already know with the effective FWHM according f-ratio for mica-spaced etalon :

http://astrosurf.com/viladrich/astro/in ... spaced.jpg

Here is the link to the data in a txt format :
http://astrosurf.com/viladrich/astro/in ... _ratio.txt

So what about the impact of the amplication of the secondary mirror of the C8 EdgeHD on telecentricity ? In fact, a divergent lens (or mirror) does not affect the telecentricity of a telecentric lens installed after this divergent lens (or mirror).

Here is the example of a PST etalon measured at 0.34 A in collimated beam, and measured at 0.76 A with the C8 EdgeHD with the f/35 Airylab telecentric, exactly as expected by the calculation.

So the last possibility could be that, for some reasons, the Quark telecentric does not like the C8 EdgeHD.
Well, the problem is that the results are about the same with my TOA 150 f/7. So maybe the Quark telecentric does not like f/7 refractors :-)

At the end of the day, this Quark is clearly not up to claimed specs.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

As a complement, the FWHM broadening depends on the f-ratio.

There is FWHM broadening even in a telecentric beam.

The difference between telecentric and non telecentric beams is that, for a same f-ratio :
- the FWHM broadening is the same on the optical axis,
- the FWHM broadening is the same on-axis and of-axis in a telecentric beam,
- the FWHM broadening increases away from the optical axis in a non telecentric beam.

The optis in front of the telecentric (reflector, refractor) does not make much difference.

Still, it is true that telecentric are optimized for a given focal length. For example, the TZ-4 is optimised for 800 mm. Still, it is quite good for 2000 mm f.l. See bottom of the page :
http://astrosurf.com/viladrich/astro/in ... lar/FP.htm


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by Bob Yoesle »

In fact, a divergent lens (or mirror) does not affect the telecentricity of a telecentric lens installed after this divergent lens (or mirror)... So the last possibility could be that, for some reasons, the Quark telecentric does not like the C8 EdgeHD.
Well, the problem is that the results are about the same with my TOA 150 f/7. So maybe the Quark telecentric does not like f/7 refractors :-)
You can't get much better for an f7 than that. Good to know Christian!
At the end of the day, this Quark is clearly not up to claimed specs.
What I would have surmised - but just wanted to give DayStar the benefit of the doubt ;-)


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by marktownley »

Very interesting Christian. I always enjoy your analysis like this.

Do you have any images taken with this Quark you can share?


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

Bob Yoesle wrote: Sat Jun 11, 2022 10:26 pm
What I would have surmised - but just wanted to give DayStar the benefit of the doubt ;-)
Sure Bob, this is important to challenge these results and double or triple check for possible sources of errors or uncertainties. This is why all your questions are very precious.

Here is the profile obtained with the Taka TOA 150. Effective f-ratio is 7.3 x 4.3 = 31.4.

http://astrosurf.com/viladrich/astro/in ... 150f31.jpg

There is a very slight increase of the FWHM due to shorter f-ratio, and in line with what would be expected for a 1 A mica-spaced etalon.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

marktownley wrote: Sun Jun 12, 2022 5:12 am Very interesting Christian. I always enjoy your analysis like this.

Do you have any images taken with this Quark you can share?
Thanks Mark,
The Quark is not mine. I had to give it back to his owner. Still, I hope to give it another try. This time on my small 55 mm f/8 fluorite refractor. This way, all focal lengths from 2 m to 0.44 m will be tested.

I will also try stopping down the TOA 150 in order to reach f/60 or so. And I'll take some pictures too :-)

Unfortunatly, I could not remove the telecentric. I had the correct Torx, but the retaining screw was really tight (probably glued).


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by Highbury Mark »

This Quark is perhaps similar to the one (also a Chromosphere model) I bought several years ago. Nice proms, but very little surface detail even at F/40. Makes you wonder how Daystar categorises Prominence and Chromosphere Quarks. I saw some beautiful images of close-up filaments and ARs taken with a Prominence model recently - it looked more like a 0.3-0.4A Quantum.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by Oak »

Very interesting! Is the FSR of 40A in line with other mica filters you have tested? My quark is more like 30A.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

Oak wrote: Tue Jun 14, 2022 5:56 pm Very interesting! Is the FSR of 40A in line with other mica filters you have tested? My quark is more like 30A.
I was really surprised by the FSR value. Other mica-spaced etalons I measured have a FSR in the range of 18 to 26 A. So, rather close to your 30 A.

I used two different approaches to measure the FSR : with the spectrograph and by interferometry with the Ha lamp. Both gave the same value plus/minus 0.5 A.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by BGazing »

christian viladrich wrote: Tue Jun 14, 2022 9:02 pm
Oak wrote: Tue Jun 14, 2022 5:56 pm Very interesting! Is the FSR of 40A in line with other mica filters you have tested? My quark is more like 30A.
I was really surprised by the FSR value. Other mica-spaced etalons I measured have a FSR in the range of 18 to 26 A. So, rather close to your 30 A.

I used two different approaches to measure the FSR : with the spectrograph and by interferometry with the Ha lamp. Both gave the same value plus/minus 0.5 A.
Please help me understand and excuse the question, 40A is actually a good thing, correct? Or is too big of a FSR value also bad?


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by BGazing »

OK, did a bit of reading and if I am not mistaken, FSR divided by FWHM gives finesse, so this one would have excellent finesse, right?


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

BGazing wrote: Thu Jun 16, 2022 7:12 pm
christian viladrich wrote: Tue Jun 14, 2022 9:02 pm
Oak wrote: Tue Jun 14, 2022 5:56 pm Very interesting! Is the FSR of 40A in line with other mica filters you have tested? My quark is more like 30A.
I was really surprised by the FSR value. Other mica-spaced etalons I measured have a FSR in the range of 18 to 26 A. So, rather close to your 30 A.

I used two different approaches to measure the FSR : with the spectrograph and by interferometry with the Ha lamp. Both gave the same value plus/minus 0.5 A.
Please help me understand and excuse the question, 40A is actually a good thing, correct? Or is too big of a FSR value also bad?
Hello,
Yes, you are right. A large FSR is not a problem at all. A large FSR means that the distance between the peaks of transmission of the etalon is large, which is a good thing because you can use a BF filter with larger FWHM (= less expensive) to isolate the peak of transmission right on Ha.
I just found it surprising because the FSR values I have found on other mica spaced etalon were in the range of 18 to 26 A.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by christian viladrich »

BGazing wrote: Tue Jun 21, 2022 7:51 am OK, did a bit of reading and if I am not mistaken, FSR divided by FWHM gives finesse, so this one would have excellent finesse, right?
Yes, this is true. But it would have been better to have the same finesse with a smaller FSR, giving a smaller FWHM as a result.

I am going a test another Quark. Just need to wait for the return of good weather. It will be 4 or 5 years old. It will be interesting to find if the FWHM and FSR remain in the same range of not.

BTW, is there a serial number somewhere on the Quark ? I can't find none.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by BGazing »

christian viladrich wrote: Tue Jun 21, 2022 8:13 am
BGazing wrote: Tue Jun 21, 2022 7:51 am OK, did a bit of reading and if I am not mistaken, FSR divided by FWHM gives finesse, so this one would have excellent finesse, right?
Yes, this is true. But it would have been better to have the same finesse with a smaller FSR, giving a smaller FWHM as a result.

I am going a test another Quark. Just need to wait for the return of good weather. It will be 4 or 5 years old. It will be interesting to find if the FWHM and FSR remain in the same range of not.

BTW, is there a serial number somewhere on the Quark ? I can't find none.
Thank you very much.
There is no serial number, but I will look at the box in which it came (right now under a pile of 'astro debris', as my wife would say), perhaps there is something on it.


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Re: Measurement of a Quark Ha filter with Sol'Ex spectrometer

Post by BGazing »

Nothing on the box except the TS note that it was checked by someone on a particular date. They do that, I understand, in order to ensure that it is not malfunctioning out of the box.


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