PST etalon spacing?

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MalVeauX
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PST etalon spacing?

Post by MalVeauX »

Hi all,

Does anyone know the exact spacing of the etalon plates on a PST setup?

I have an extra PST etalon but its spacers are missing for some reason between the plates. The original owner either mistakenly removed them lost, lost them, etc and so the etalon appears decontacted, but actually its most probably that it lacks any spacers at all.

Very best,


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Re: PST etalon spacing?

Post by christian viladrich »

Hello Marty,
On one PST, I measured a cavity gap of 0.2316 mm plus/minus 0.0003 mm. On another PST, I measured a spacing of 0.311 plus/minus 0.001 mm. Maybe the thickness of the spacers changes with generation of PST ? Or with coatings ? I don't know.

For what is worth, this is not a direct measurement of the thickness of the spacers, but a measurement of the cavity gap by interferometry.
The measurement includes the fact that the cavity gap is not uniform over the area of the etalon (central spacer and out spacer seem to have slightly different thickness).

In anycase, the thickness of the spacers should be very accurate in order to tune on Ha.

Maybe, you can contact Oliver at Beloptik. He knows quite a bit about that. And also people at Coronado/Meade.


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Re: PST etalon spacing?

Post by vkx86 »

Take a look on that PST etalon restoration video.
Translate from Russian to English works quite well.
He used thin covering glass that is used in microscopy to find appropriate pieces of glass to use as spacers.


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Re: PST etalon spacing?

Post by christian viladrich »

vkx86 wrote: Sat Mar 19, 2022 6:04 am Take a look on that PST etalon restoration video.
Translate from Russian to English works quite well.
He used thin covering glass that is used in microscopy to find appropriate pieces of glass to use as spacers.
This is an excellent video ! Thanks for sharing. A link to bo be saved preciously.


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Re: PST etalon spacing?

Post by christian viladrich »

christian viladrich wrote: Sat Mar 19, 2022 9:42 am
vkx86 wrote: Sat Mar 19, 2022 6:04 am Take a look on that PST etalon restoration video.
Translate from Russian to English works quite well.
He used thin covering glass that is used in microscopy to find appropriate pieces of glass to use as spacers.
This is an excellent video ! Thanks for sharing. A link to be saved preciously.


Christian Viladrich
Co-author of "Planetary Astronomy"
http://planetary-astronomy.com/
Editor of "Solar Astronomy"
http://www.astronomiesolaire.com/
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Re: PST etalon spacing?

Post by vkx86 »

christian viladrich wrote: Sat Mar 19, 2022 9:42 am This is an excellent video ! Thanks for sharing. A link to bo be saved preciously.
It's my genuine pleasure to share useful information with community, from which I'd learned so much (you included)!


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Re: PST etalon spacing?

Post by MalVeauX »

Thanks! I have things to try! Appreciate it!

Very best,


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