Measured finesse of the Coronado SM60 etalon.

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Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

The attached graph was obtained with a Spectra-L200 (1800 l/mm) spectroscope.
The dispersion was 0.29A/pixel, resolution, approx. 0.7A
This shows the transmission "comb" of the SM60 etalon around the Ha wavelength. Where the "peak" is reduced, shows the etalon to be "on-band" to the Ha line.
Measurements indicate a spacing of 11A, and a FWHM bandwidth of approx. 1A
(The other transmission lines at either side of the Ha line are blocked by the final blocking filter when in use.)
Hope this is of interest.
SM60 Finesse.JPG
SM60 Finesse.JPG (80.92 KiB) Viewed 4464 times


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Re: Measured finesse of the Coronado SM60 etalon.

Post by marktownley »

Very interesting indeed Ken! Do you have any solid etalons you could repeat the experiment on?


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

Mark,
You mean Daystar type?
No, only Coronado......


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Re: Measured finesse of the Coronado SM60 etalon.

Post by swisswalter »

Hi Ken

fantastic measurement. Thank you for sharing


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

Thanks Walter.
It's an ideal way of checking (and confirming) the etalon performance.
I had thought the bandwidth was better than 1A.......


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Re: Measured finesse of the Coronado SM60 etalon.

Post by swisswalter »

Hi Ken

it's like fuel consumption with cars. Paper is very forgiving ;)


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Re: Measured finesse of the Coronado SM60 etalon.

Post by mdwmark »

I was wondering how many people would say, Why are the HW about 1 Ang when it should be narrower.
Even thou the camera chip is .29A/pixal the spectrometer with that focal length can not resolve the bandwidth. It would take a 3/4 meter focal length to resolve that HW. So it does best it can and shows you at what wavelength the peaks are at. What surprises me is that at the zero (or bottom) of the curve they should all be coming to the same count in that small range of wavelengths. Not sure what that is about.
Mark W.
Attachments
IMG.pdf
scan with a small spectrometer
(670.63 KiB) Downloaded 121 times


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Valery »

I am wondering why the H-a peak is so small vs other peaks. So small transmission here!

Ken, Mark W., can you explain why?

Thanks,

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Re: Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

Valery,
I didn't mention in the post, but this is a solar spectrum. The dark Ha absorption line is sitting in the transmission "peak" of the etalon therefore that one peak appears "lower".
If the etalon was sitting "off band", then the Ha absorption wouldn't show up, and all the transmission peaks would be similar.
HTH


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Re: Measured finesse of the Coronado SM60 etalon.

Post by mdwmark »

Hi, I forgot to say that the etalon was about .7Ang wide. But the spectrometer has no problem resolving the 1nm bandpass. On the attachment to my last post
The spectrometer is an HR 4000 (Ocean Optics) with a 5 micron slit.
Mark W.


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

Mark,
Any chance of getting similar data for the Lunt etalons and their blocking filters?
There seems to be at least some differences between the Lunt and Coronado blocking filters......


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Re: Measured finesse of the Coronado SM60 etalon.

Post by alex »

Nice review Ken!

Thanks for sharing.

This might be interesting too http://www.astroshot.com/Solar/Solarmax60-analysis.pdf


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

Alex,
Thanks for that.
I was the one who posted it to the library ;)


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Re: Measured finesse of the Coronado SM60 etalon.

Post by mdwmark »

Hi Ken,
I don't think that I should post scans of other bandpasses that I didn't make.
I don't want to have any conflict of interest. I just keep the posts as another guy that likes solar.
Mark W.


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Gert »

Hi Merlin66,

From your discussion it appears that you used the sun as the light source.
Why did you not use a reference light source without spectral features like a high pressure arc lamp?

Cheers,
Gert


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Re: Measured finesse of the Coronado SM60 etalon.

Post by Merlin66 »

Gert,
It was an opportunistic capture. I was testing an SM90 and used my SM60 for comparison.
If I were doing a "proper" analysis, yes, a Quartz lamp, full calibration with darks, flats and instrument response would be the way to go.
It was posted to show the members the etalon comb and typical spacing....


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