another PST stage 2 mod

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bart1805
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Re: another PST stage 2 mod

Post by bart1805 » Sat Sep 08, 2018 8:15 pm

And now it is a small step to doublestack the etalons. (-;

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pedro
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Re: another PST stage 2 mod

Post by pedro » Sat Sep 08, 2018 9:47 pm

Hi Bart

I have a BIG soft spot with both etalons. Very different from my other H-alpha systems


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Re: another PST stage 2 mod

Post by Starry Jack » Tue Oct 02, 2018 8:20 pm

Pedro,
In your excellent document (http://astrosurf.com/re/PST_Stage_2_Mod ... 180911.pdf), you mention the focus must come to a point 244mm from the rear of the rubber on the etalon. Where is that on your scope? The top of the diagonal? The middle of the eyepiece?


I've cobbled together a prototype yesterday using some pretty strange spare parts but it should work.

The other question is...I am using parts of a standard 2x barlow rather than the Glasspath. I've figured out the mounting in the prototype but does it need to be telecentric?

Thanks,
Jack

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Re: another PST stage 2 mod

Post by pedro » Wed Oct 03, 2018 10:03 am

The measurement was made by Ken Harisson:

Ken Harrison (2005). Modifying a Coronado PST Hα Solar Telescope (PDF file).

The PST etalon must be correctly placed. Final focus should be 225 mm behind the rubber ring of the etalon.

You can use other parts, a X2 barlow should work fine. It needs to be telecentric

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Re: another PST stage 2 mod

Post by Starry Jack » Wed Oct 03, 2018 2:41 pm

Thanks, Pedro. I think my only confusion is where "final focus" is. I only use a video camera (no visual). Is that at the exit of the blocking filter? Or is it measured at the sensor chip? Or somewhere in between?

Best,
Jack

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Re: another PST stage 2 mod

Post by pedro » Wed Oct 03, 2018 2:49 pm

Hi Jack

I tried several configurations and found out that a distance of 14cm from the rear of the PST etalon to the Coronado BF, works fine

Imagesolar_imaging_session_20180830-03 by Pedro Ré, on Flickr

ImagePST_stage_2_mod_20180830-032 by Pedro Ré, on Flickr

I did not reduce the OTA's length (did not cut the tube)

regards

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Re: another PST stage 2 mod

Post by Starry Jack » Wed Oct 03, 2018 8:37 pm

Got it. And I also found the document you referred to so I should be good to go. The biggest difficulty seems to be finding an ok n-stock telecentric lens.

Jack

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Re: another PST stage 2 mod

Post by marktownley » Thu Oct 04, 2018 5:07 pm

None of the lenses in this system are telecentric Jack - totally different thing!
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