Adapter for doublestacking PST etalons

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bart1805
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Adapter for doublestacking PST etalons

Post by bart1805 » Fri Jan 18, 2019 1:25 pm

Hi everybody,

Ken asked me a question about my 3D printed adaptor to doublestack two PST etalons. It was a succes as far as printing M50x1 was concerned. But when I used the adaptor you could see extreme banding in the images.
The 3D printed adaptor looked like this:

ImageThe adaptor before sanding by bart moors, on Flickr

And here you can see the banding:

Image040917_10.21_BR127_DS_PM2,5x_AR2673 by bart moors, on Flickr

After that I asked Beat (AOK) to make me an adaptor. He made one and it worked almost the same as the 3D printed one: a lot of banding. The big advantage of the AOK adapter is that you can "radially tune" the adaptors, but the banding was still there. The wisdom of the forum told me to use a Circular Polarizer. Unfortunately with a CP mounted inside the adaptor, it was a bit short. So I also needed the 3D printed adapter. With a bit of tape and a piece of a toothpick I could hold the CP at its place. This was a succes!
Here are some pictures of the AOK adapter:

Image20190118_140237_resized by bart moors, on Flickr

Image20190118_140245_resized by bart moors, on Flickr

Image20190118_140302_resized by bart moors, on Flickr

And here is how it looks when the two PDT etalons are doublestacked. Front one without backlens, the other one without the frontlens.

Image20190118_140742_resized by bart moors, on Flickr

From right to left:
Etalon B
3D printed adaptor
AOK doublestack adapter
Etalon A
AOK adaptor to mount the etalon in a SCT focuser.

And two DS pictures:

Image24092017_14h58m_Br127_DS_PM2,5x_AR_PSV2 by bart moors, on Flickr

Image230917_14h07m_Br127_DS_PM2,5x_AR_PS_Inverted by bart moors, on Flickr

It would be perfect if you could rotate the CP while maintaining the alignment and orientation of the etalons. Ken suggested the following:
Two side access holes/ slots and using a smaller internal filter thread (37mm CPL diameter?) in the adaptor. The outer edge of the rotating filter could be accessed through the side slots. I just thought of another problem because you have to mount the adaptor "the other way around".
Has anyone got another idea how this could be realised? Or an idea for the ultimate 2.0 version?

And is anybody interested in this adapter? If so I can ask Beat to make a price for a couple of these adaptors. Ken and I will both order one if the price is decent. No meaning to earn anything out of it, you pay what Beat asks. If it would cut the costs any further I can pay for all the adaptors and ask Beat to ship the adaptors to me so I can ship them from the Netherlands all over the world. My original AOK adaptor costed CHF 60,--. So that is about $61,--. Honestly don't know what the 2.0 version would cost. I will let you know if you are interested.

CS!
Bart.

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Re: Adapter for doublestacking PST etalons

Post by MalVeauX » Sat Jan 19, 2019 1:20 pm

Very interesting, I certainly would be interested and to see how this develops and would probably buy too!

Very best,

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Sat Jan 19, 2019 4:07 pm

This would probably be the best candidate to serve as the 37mm CP:
https://www.ebay.com/itm/B-W-37mm-XS-PR ... :rk:9:pf:0

And the possibility to rotate the CP 90 degrees seems to be sufficient?

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Re: Adapter for doublestacking PST etalons

Post by marktownley » Sat Jan 19, 2019 6:30 pm

Nice adapter Bart
Image
http://brierleyhillsolar.blogspot.co.uk/
Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Tue Jan 22, 2019 10:43 pm

Two ideas for the Circular Polarizer. The first one is from Apollo.
https://www.bhphotovideo.com/c/product/ ... izing.html
https://www.teleskop-express.de/shop/pr ... esign.html

The latter one is a whole lot cheaper and pretty simple. On the front:
Nosepiece with M50x1 female, back male M48. 2,5 to 3 cm long.
On the back:
M48 female adapter to M50x1 male including the ring to radially tune the etalons. Length about 3 cm.

Total length would be about 7,5 to 8 cm. That is the same as the AOK adapter plus the 3D printed adapter plus the optical path of the filter changer. And off course would need a ring to mount the current 46 mm polariser in the filter drawer.
If everything is mounted it is easy to take the filter drawer out to twist the polariser.

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Re: Adapter for doublestacking PST etalons

Post by Merlin66 » Wed Jan 23, 2019 2:52 am

Bart,
I have a set of the Neumann filter drawers. Could use a standard 1.25” CPL filter.
Just needs a couple of T thread to M50 Adaptors?
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Wed Jan 23, 2019 10:33 am

I think you are right Ken. I would like to use the B+W circular polarizer because it has a high transmission (the filter has to be placed backwards btw).
Plus the back adapter needs the extra ring so you can position the back etalon to the front etalon and hold it that way. So the shopping list would be:
1) A filter drawer
2) Front adaptor, relatively simple. M50x1 female at the front. Thread to the drawer at the back.
3) Back adapter with the extra ring to hold the etalon in the position you want it to be. Front is thread to drawer. Back is M50x1 male
4) CPL and possibly a retaining ring to mount the CPL in the filter drawer.

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Re: Adapter for doublestacking PST etalons

Post by Merlin66 » Wed Jan 23, 2019 11:29 am

Yeah, that sounds about right!
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Sat Jan 26, 2019 3:08 pm

This could be another possibility to rotate the CP.
Two of these, in between them a short T2 extension with the CP mounted inside.
https://www.teleskop-express.de/shop/pr ... short.html

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Re: Adapter for doublestacking PST etalons

Post by Merlin66 » Sun Jan 27, 2019 12:18 am

Bart,
We have used these T2 rotators for some years on the spectroscopes - work well...
You can also get a T thread to 1.25" filter thread adaptor ......
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Sun Jan 27, 2019 12:42 am

Hi Ken,
Nice! And can they handle the load? In my case there is quite a lot of weight hanging after the etalon because a JMI focuser is included.
I asked Gerd Neumann if he is able to produce his filter drawer with different threads on the front and back. Is is in your mail too.
- on the front side 21 mm M50x1 female
- on the back side 20 mm M50x1 male.
- plus a ring about 7mm thick, 7cm high with M50x1 female on the inside. The ring is needed so you can clock the two etalons against each other and retain the ideal position.
CS! Bart.
ps. Maybe it is also time to get rid of the focuser in the imaging train and go for a simple 20cm distance from the last etalon to the camera.

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Re: Adapter for doublestacking PST etalons

Post by Merlin66 » Sun Jan 27, 2019 12:50 am

Bart,
The T rotator was holding the ATiK 314 camera on the rear of the spectrograph...no issues.
I'm using a short Lunt Crayford focuser on the SM60/ED80/PST mod DS - I find it very useful, when changing cameras and or barlows etc.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Sun Jan 27, 2019 12:56 am

You are right Ken, it is useful. The JMI weighs about 600 - 700 grams I think.

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Re: Adapter for doublestacking PST etalons

Post by Merlin66 » Sun Jan 27, 2019 1:05 am

The ATiK 314L is 400gms.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Sun Jan 27, 2019 9:22 pm

Gerd Neumann responded that he is able to make the adaptors for a standard filter drawer and is able to make a drawer with the M50x1 threads on the front and back. Will make some drawings and send these to him.
Apollo is working on another solution, based on a dovetail concept. Very interesting too!

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Re: Adapter for doublestacking PST etalons

Post by bart1805 » Sat Feb 02, 2019 9:31 pm

I think it is as simple as in this drawing:

ImageScan 3 by bart moors, on Flickr

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