127mm PST Mod - day 1

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127mm PST Mod - day 1

Post by marktownley » Tue Jun 26, 2012 9:51 pm

Well I finally adapted the cell for my 110mm Baader D-ERF to mount it internally in the tube in my 127mm Meade AR5 frac; all fitted well. By some freak of weather the clouds broke so was able to setup outside for first light. Upon looking through the eyepeice all was not right - I know the AR5, particularly at narrowband wavelengths is a fraunhofer refractor capable of some pin sharp views, the views I was getting were not inline with the norm. Focus was not consistent across the fov...

The clouds returned so I headed inside and over a can of Orangeboom pondered what I had seen; deciding to back track I think I have located the cause of my issues - When I took the fraunhofer lens out of the cell I may have put it in back to front :whistle:

Anyway, has been replaced the right way round now, however not going to be able to try it out till friday afternoon at the earliest - 2 late days at work coming up... Should be fun when its up and running though :silly:
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Re: 127mm PST Mod - day 1

Post by swisswalter » Wed Jun 27, 2012 4:30 am

Hi Mark

thanks for the news. Good luck on the weekend. Looking forward to your pics
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: 127mm PST Mod - day 1

Post by marktownley » Sat Jun 30, 2012 10:28 am

Thanks walter! I'm chancing the cloud breaks and showers today - setup with a big waterproof sheet incase of emergency.

Objective in the 127mm is now the right way round and OMG, the views, wow, whether through the eyepeice or on live view in ICCapture - the jump from 4" to 5" is really quite amazing - much more than I thought!

Whilst sorting the objective out I also decided to bite the bullet and disassemble the housing for the PST etalon using the diagrams in the patents as a guide (they're very useful!). I've now realigned the etalon with respect to its housing and the compressive rubber rings, and now the sweetspot is aligned dead centre with the fov, not off centre as was before.

Now, all I need is a big enough cloud gap, there's plenty see on el-sol today to test out my new creation! :)
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Re: 127mm PST Mod - day 1

Post by Merlin66 » Sat Jun 30, 2012 10:33 am

Mark,
Did you take any photos while dismantling the PST assembly???
(There's not much real documentation available)
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Re: 127mm PST Mod - day 1

Post by marktownley » Sat Jun 30, 2012 10:51 am

I didn't, but I am going to recollimate my friends etalon i've been borrowing, so will document this with some pics ;)

It really is a straightforward peice of kit... I think most pst etalons would benefit from the method...
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Re: 127mm PST Mod - day 1

Post by marktownley » Sat Jun 30, 2012 10:56 am

I really hope the pics i'm getting (from the DMK) come out - the detail i'm getting is awesome!

I'm going to have to start searching for large aperture f10 fracs I think :whistle:
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Re: 127mm PST Mod - day 1

Post by Merlin66 » Sat Jun 30, 2012 11:06 am

Mark,
The PST etalon acts as an aperture stop and limits the f ratio to f10 or greater.
If the AR5 is 125mm and f9, the focal length will be 1125mm.
This means that the effective aperture with the PST mod will be 1125/10 = 112.5mm
If you go up (again!) to a 150mm f8, this gives a 120mm effective aperture......
"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: 127mm PST Mod - day 1

Post by swisswalter » Sat Jun 30, 2012 12:57 pm

Hi Mark

great news. Do you have a cloud gap? I'm eager to see your first light ;)
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: 127mm PST Mod - day 1

Post by robert » Sat Jun 30, 2012 1:10 pm

Mark,
The PST etalon acts as an aperture stop and limits the f ratio to f10 or greater.
If the AR5 is 125mm and f9, the focal length will be 1125mm.
This means that the effective aperture with the PST mod will be 1125/10 = 112.5mm
If you go up (again!) to a 150mm f8, this gives a 120mm effective aperture......

How does jpb get such high res shots with AP155 f8.5 PST mod?
http://jp-brahic.chez-alice.fr/soleil290612.htm

I think there must be more to this story?

Robert
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ED80. SW200. Celestron-150mm-PST mod
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Re: 127mm PST Mod - day 1

Post by Merlin66 » Sat Jun 30, 2012 1:16 pm

A 155mm f8.5 would still give an effective aperture of almost 132mm - that's certainly big enough to give, under excellent seeing conditions, a very good surface resolution...the bandwidth comes down to the quality of the PST etalon.
Unless you go to a Marcon type solution using "external" collimated etalons, then you are restricted to the f10 limitation - such is life.
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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Re: 127mm PST Mod - day 1

Post by marktownley » Sat Jun 30, 2012 1:51 pm

Oh yes Walter, i got my gap ;)

I agree too Robert, there is more to this than meets the eye...
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Re: 127mm PST Mod - day 1

Post by swisswalter » Sat Jun 30, 2012 4:19 pm

Hi Mark

great , where are the shots? I just made my first light with the 127mm mod 2 and have to stack them. See you soon ;)
Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)

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Re: 127mm PST Mod - day 1

Post by Merlin66 » Sun Jul 01, 2012 1:31 am

It's pretty straight forward, the front barlow element is -200mm focal length and 20mm diameter.
When this is correctly placed in a f10 converging light cone, it's fully illuminated ( and provides the maximum collimated beam to the etalon).
If it's placed say in a f6 light cone, the diameter of the beam at the -200mm position will be 200/6 = 33mm, too large to be accepted by the barlow...this beam will be "stopped" down to the 20mm max, resulting in a reduction of the effective aperture of the scope.
The end result is always the f10 beam.
Hope this helps....
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Re: 127mm PST Mod - day 1

Post by peter drew » Sun Jul 01, 2012 10:08 am

Excellent explanation of the F10 requirement Ken, really usefull for those contemplating going up in aperture. As to how such good images are achieved with an AP F8, apart from conditions and the skill of the imager, I think a clue is in the prefix AP, good quality optics deliver good images. :)

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Re: 127mm PST Mod - day 1

Post by marktownley » Sun Jul 01, 2012 12:06 pm

It's pretty straight forward, the front barlow element is -200mm focal length and 20mm diameter.
When this is correctly placed in a f10 converging light cone, it's fully illuminated ( and provides the maximum collimated beam to the etalon).
If it's placed say in a f6 light cone, the diameter of the beam at the -200mm position will be 200/6 = 33mm, too large to be accepted by the barlow...this beam will be "stopped" down to the 20mm max, resulting in a reduction of the effective aperture of the scope.
The end result is always the f10 beam.
Hope this helps....

Soooo, theoretically, if one replaced the f10 collimating lenses in a PST etalon assembly for ones that matched the focal ratio (assuming we obviouslly keep 20mm diameter) of the scope ota being used - f8,f9 etc, then we could stop the vignetting?
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Re: 127mm PST Mod - day 1

Post by robert » Sun Jul 01, 2012 12:26 pm

As to how such good images are achieved with an AP F8, apart from conditions and the skill of the imager, I think a clue is in the prefix AP, good quality optics deliver good images. :)

I think this might be important too :( unfortunately for me
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2017 images http://tinyurl.com/gvk9k3k
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Re: 127mm PST Mod - day 1

Post by Merlin66 » Sun Jul 01, 2012 12:47 pm

Mark,
Theoretically yes...
This is what Marcon basically does with his "bare" etalon mod....
In the Lunt60 mod we found the focal length of the barlow was 1/1.85 that of the imaging lens..
"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: 127mm PST Mod - day 1

Post by marktownley » Sun Jul 01, 2012 1:03 pm

Mark,
Theoretically yes....

Really!!! It's never normally that simple!

Sooooo, next question then is what 'sort' of lens is needed to achieve this?
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Re: 127mm PST Mod - day 1

Post by Merlin66 » Sun Jul 01, 2012 1:13 pm

A suitable telecentric would do the job!
What ever you consider must at least be 20mm clear and a f ratio/ negative focal length to match your scope..
If it's an f9 system - then a good barlow -180mm focal length might be a good start.
Edmund Optics only go to -150mm
http://www.edmundoptics.com/optics/opti ... c#products
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
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Re: 127mm PST Mod - day 1

Post by marktownley » Sun Jul 01, 2012 1:32 pm

Hmmm, it's number juggling with stock lenses then...
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Re: 127mm PST Mod - day 1

Post by marktownley » Sun Jul 01, 2012 6:37 pm

Mark,
The PST etalon acts as an aperture stop and limits the f ratio to f10 or greater.
If the AR5 is 125mm and f9, the focal length will be 1125mm.
This means that the effective aperture with the PST mod will be 1125/10 = 112.5mm
If you go up (again!) to a 150mm f8, this gives a 120mm effective aperture......

But a 150mm f10 would work as a 150mm f10?
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Re: 127mm PST Mod - day 1

Post by peter drew » Sun Jul 01, 2012 6:47 pm

Yes Mark, this is what I use, a 150mm F10 objective from Istar. :)

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Re: 127mm PST Mod - day 1

Post by marktownley » Sun Jul 01, 2012 9:24 pm

A 6" f10 is going to be my next step I think, although after today I was struggling with the 5" with the poor seeing - maybe I should have used the 4" :whistle:
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Re: 127mm PST Mod - day 1

Post by Richard » Tue Jul 03, 2012 3:42 pm

Sound interesting Mark, look forward to the results. Still collecting the items I need for the Vixen custom 80 mod. Just taken the tube etc to a powder coating company (as the weather is forcast to be rain for the next few days/weeks/months.....
And with it being about 30 years old it was a bit scratched. They are blasting it back to bare metal then priming and coating it... (They are doing it gold colour so will see what its like when I get it back).... :hamster: (got a 127mm refractor aswell, but may need to do a brace system like I see you have as the slightest wind blows it all over the place.
What did you use for yours? looks very intersting...
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Re: 127mm PST Mod - day 1

Post by colinsk » Tue Jul 03, 2012 11:43 pm

For aiming purposes we try to have a telescope mounted by a single point. If we polar align the optical axis to a polar alignment then we can mount the scope in two or more points and simply rotate a single mirror.

Bob Hess has a great example in "Amateur Astronomy #59 by Robert Hess" of a heliostat feeding a TV85 with a T-Scanner in a oven.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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