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Transit of Mercury in the Spicule Layer. Phil took this great image with his Quantum 6 Scope, Solar Spectrum etalon and PGR Camera.

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Second go at 150mm Mod

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Second go at 150mm Mod

Post by solar » Sun Mar 16, 2014 5:34 am

Had another go at this contraption today. Extremely seeing dependent and wind is a major factor with the length of the scope.
Conditions were better today and seeing had improved a bit.
Not as good as Valery or Neo but I am getting there.
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Vixen 130ss SolarMax 90 BF30 EQ6 Pro, LX200 12", C8 CG5, Megrez80, SBIG2000 MXC,

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Skywatcher 150mm PST Mod2

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Re: Second go at 150mm Mod

Post by axlefoley » Sun Mar 16, 2014 5:50 am

Pretty good Ralph

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Re: Second go at 150mm Mod

Post by mattwastell » Sun Mar 16, 2014 6:00 am

Looking good Ralph - I will look forward to your progress with this cannon!
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Re: Second go at 150mm Mod

Post by Derek Klepp » Sun Mar 16, 2014 6:21 am

Excellent Ralph the colour one is really good.You didn't nab any of that filament did you?

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Re: Second go at 150mm Mod

Post by edobosz » Sun Mar 16, 2014 6:28 am

Yep, looking good ralph. I am intending to tinker with my DSII unit from my Lunt 80 and put it onto a 127mm unit to see what comes of it.
What ERF are you using?
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Re: Second go at 150mm Mod

Post by solar » Sun Mar 16, 2014 6:56 am

Asimov wrote:What's all that gear hanging off the arse end of it? You'll be getting flexure/sag from that surely...Nice work mate.
That's half your PST with a BF28 and barlow plus camera. No issues with flexing or sag as it is all top quality machined fittings. :band
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Re: Second go at 150mm Mod

Post by solar » Sun Mar 16, 2014 6:58 am

edobosz wrote:Yep, looking good ralph. I am intending to tinker with my DSII unit from my Lunt 80 and put it onto a 127mm unit to see what comes of it.
What ERF are you using?
Ted
150MM full aperture ERF mount externally Ted.
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Re: Second go at 150mm Mod

Post by Valery » Sun Mar 16, 2014 7:12 am

solar wrote:Had another go at this contraption today. Extremely seeing dependent and wind is a major factor with the length of the scope.
Conditions were better today and seeing had improved a bit.
Not as good as Valery or Neo but I am getting there.
Very good shots!

I belive that your mod is PST stage 2. Right?
The main difference with my mod is that my mod is designed for full solar disk at 0,7 - 0,8A and for half disk size at 0.5A.
PST mod allows barely 1/5 disk at 0,8-0,9A with 150mm telescope. Too small etalon size compare to the objective size.
Also, the optics in my mod is fully optimized for a given 150mm optics. Collimator and refocused lenses in PST are not
strictly designed for all other scopes even if they are close to F/10. This can soften images somewhat.

Regards,

Valery.
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Re: Second go at 150mm Mod

Post by marktownley » Sun Mar 16, 2014 7:32 am

Top shots Ralph, you'll get used to this new big gun!

Interesting info there valery...
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Re: Second go at 150mm Mod

Post by solar » Sun Mar 16, 2014 7:33 am

Valery wrote:
solar wrote:Had another go at this contraption today. Extremely seeing dependent and wind is a major factor with the length of the scope.
Conditions were better today and seeing had improved a bit.
Not as good as Valery or Neo but I am getting there.
Very good shots!

I belive that your mod is PST stage 2. Right?
The main difference with my mod is that my mod is designed for full solar disk at 0,7 - 0,8A and for half disk size at 0.5A.
PST mod allows barely 1/5 disk at 0,8-0,9A with 150mm telescope. Too small etalon size compare to the objective size.
Also, the optics in my mod is fully optimized for a given 150mm optics. Collimator and refocused lenses in PST are not
strictly designed for all other scopes even if they are close to F/10. This can soften images somewhat.

Regards,

Valery.
Yes Valery it is the Mod 2. Not sure I am following you with your setup. Can you post some shots an a bit more info please.
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Skywatcher 150mm PST Mod2

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Re: Second go at 150mm Mod

Post by GeorgeIonas » Sun Mar 16, 2014 9:58 am

Ralph, the resolution you are getting is just awesome - all stunning images.

George
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Re: Second go at 150mm Mod

Post by Merlin66 » Sun Mar 16, 2014 10:48 am

Geez,
Not bad for a 20mm PST etalon!!
Great set up.....
I'm sure, given the good seeing conditions you usually get, that you'll soon be posting even more exciting images.
Well done!
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Re: Second go at 150mm Mod

Post by Merlin66 » Sun Mar 16, 2014 10:51 am

Valery,
Why do you say the PST etalon is not so hot with larger scopes even at f10....the etalon doesn't know what's up front, only that the "usual" f10 beam is entering and it's in its "usual" position 200mm inside focus....
"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.yahoo.com/neo/groups/ast ... scopy/info
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"Imaging Sunlight - using a digital spectroheliograph" - Springer


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Re: Second go at 150mm Mod

Post by Valery » Sun Mar 16, 2014 5:33 pm

Merlin66 wrote:Valery,
Why do you say the PST etalon is not so hot with larger scopes even at f10....the etalon doesn't know what's up front, only that the "usual" f10 beam is entering and it's in its "usual" position 200mm inside focus....
Several things:

1. Acceptance angle of any etalon is about 1 degree if the etalon works in quazy parallel light beam. in a front of an objective.
2. For internally working etalons there is a rule: acceptance angle = d/D degree where d is etalon diameter and D is objective diameter.
For a given case, 20mm etalon in a 150mm scope the acceptance angle is about 1/3,5 - 1/4 of the sun disk if the band wide is 0,7A.
For wider band wide, say, typical 0.9, acceptance angle can be even solid 1/3 of the sun disk.
3. PST etalons are quite vary in band wide - some of them are even at 0,7A, but most are around 0,9A.
4. Even if the collimator-refocused optics in the PST is F/10, this does not necessary mean that it will not add some aberrations or will not undercompensite some aberrations of another systems F/10 different to what it was designed for. SA in Ha, field curvature, astigmatism are different for 40mm F/10 and 150mm F/10 objectives and may between. So, the PST optics does not work at best in another F/10 systems, not say in F/X systems which are not F/10.
Of course, image processing and contrast increasing makes this problem less noticeable, but absolutely not fix it and PST etalon itself will works better with specially designed optics for larger donor objective.

If to take as an example the mod by ARIES, the etalon is 2,5x larger and the optics is FULLY optimized for a given 150mm F=750 SW refractor.
All aberrations are nullified and 0,8 degree field is really ideal in Ha. This is one of the main factor of good images this system produce.

But, of course, PST mod, especially mod-2 is a very cost effective mod for Ha telescopes, just with it's native limitations. And this images in this thread show it's potential which is high enough within smaller FOV.


Regards,

Valery.
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Re: Second go at 150mm Mod

Post by Merlin66 » Sun Mar 16, 2014 7:39 pm

Valery,
Thanks for that.
I think the only difference, possibly, could come from the change in objective. The PST has a very basic achromat and I'd assume a similar achromat in the donor would give similar performance.

Your rule:
For internally working etalons there is a rule: acceptance angle = d/D degree where d is etalon diameter and D is objective diameter

I haven't heard this before...could you give more details?
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Re: Second go at 150mm Mod

Post by Valery » Sun Mar 16, 2014 8:18 pm

Merlin66 wrote:Valery,
Thanks for that.
I think the only difference, possibly, could come from the change in objective. The PST has a very basic achromat and I'd assume a similar achromat in the donor would give similar performance.
There is NO such basic achromat as a 40mm F/10. An 80mm F/10 achromat will have 2x larger spherical aberration at 656nm than a 40mm F/10.
A 150mm achromat F/10 will have almost 4x larger SA at 656nm. So, images in these telescopes will be aggravated by a larger, uncorrected SA.
Also, the collimation-refocusing block of the PST corrects a field curvature of a 40mm F/10 achromat - the radius of curvature of the focal plane of a 40mm F/10 achromat is about 140mm, while radius of curvature in 150mm F/10 achromat is about 545mm. So, the field in PST mod with 150mm F/10 will not be flat and will have negative field curvature - images at the edge will be softer. And so on and so on.

If you don't believe, you can check this will optical design software.
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Re: Second go at 150mm Mod

Post by solardave » Sun Mar 16, 2014 8:35 pm

fantastic ralph good job :bow
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Re: Second go at 150mm Mod

Post by Merlin66 » Sun Mar 16, 2014 9:06 pm

Valery,
OK I see your point!
What about the d/D rule??
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Re: Second go at 150mm Mod

Post by marktownley » Mon Mar 17, 2014 9:49 am

Without wanting to hog this thread, or send it off in another direction, i'm really interested in further understanding the issue of spherical aberration in our mod scopes and how we can improve matters optically. I will start a thread in the mod section, I do hope you can join us there Valery! :)
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Re: Second go at 150mm Mod

Post by solar » Mon Mar 17, 2014 10:07 am

marktownley wrote:Without wanting to hog this thread, or send it off in another direction, i'm really interested in further understanding the issue of spherical aberration in our mod scopes and how we can improve matters optically. I will start a thread in the mod section, I do hope you can join us there Valery! :)
Me too Mark, very interested, and thanks.
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Re: Second go at 150mm Mod

Post by swisswalter » Tue Mar 18, 2014 5:42 am

Hi Ralph

wonderful results and great discussions on that thread
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