C8 + PST?

Frankenscope? Let's see it!***be advised that NOTHING in this forum has been safety tested and you are reading and using these posts at your own peril. blah, blah, blah... dont mess around with your eyesight when it comes to solar astronomy. Use appropriate filtration at all times...
Post Reply
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

Hi Bob,

Thanks a lot for your info.

My SM40 has no tilt at all to be in CWL or very near it. And what I have found is that this etalon
starts to work at the very limit of usefulness if the atmospheric pressure reached 772mm Hg.
It works best at 762mm Hg and require a bit of tilt at 755-760mm Hg.

So, I see that 15mm Hg is almost a limit for CWL shift to the blue wing. If your first etalon does not
require any tilt at all at the 612m elevation, then it should not work at 15m elevation - too much
blue shift and no any tilt will help, just opposite. May be it still require a bit of tilt.

To realize if it require a tilt or not, peform the easy test: use a magnification when the FOV is about
1.5 degree. Better 90 or 100 degree eyepiece. Adjust the etalon for maximal contrast in the center of the FOV.
Then move the sun across the FOV in perpedicular directions - along with tilt mechanism and perpendicularly.
See the size of the sweet spot. If no tilt, the sweet spot will be equal along both directions. If there is a tilt,
then you have a banding and the sweet spot size will be different - smaller along of the tilt mechanism direction.

If you ever decide to sell your first etalon SM90, I will be the first in the turn for it.

Valery.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

If both etalons are designed to be tilt tuned ( I had a pair of external SM60 etalons with T max tuning), then I'd also assume that the "design" wavelength would be slightly above Ha to allow the tilt tuning into "band" and then onto the blue.
I have use the etalons as single stacks (on the ED80) and with the PST as a double stack, and this seems to be the case for me.
What this infers to me is that when the second etalon is tilted to remove the "ghosts in the machine" we must be tuning it, probably into the blue wing, and when combined as a DS ( with the other etalon on band) the overall FWHM will still be there, very slightly towards the blue, but the intensity of the image reduced.
Does this make any sense?


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

Ken,

In the ideal pair of etalons for DS both etalons must require a little tilt - 2x smaller than than in the second etalon
in the case of first etalon has no tilt and second etalon has a minimal tilt when the ghost is a bit farther than a
touch (to allow full disk and prominences be not blended with the ghost).
And need to be clocked so, that they move the ghost in the same direction. In this given case the resulting delta Lambda
will be smallest.

As for your second case with blue shift for a second etalon. You will not reach narrower FWHM. It will stay the same,
but the S/N will be worser.


Valery.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

Valery,
We had a spreadsheet (probably still in the files area) which shows the reduction in FWHM with etalons slightly off-set to each other. Such an arrangement of, say, double 0.7A etalons does indeed give a FWHM of around 0.4A. The intensity peak is reduced, so I suppose you could say there's a lower SNR.
Added: If you tilt the front element say 1 degree to push the "ghosts" from the FOV, this would, based on Bob's graphs, move the CWL towards the blue by 0.4A.


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

Merlin66 wrote:Valery,
We had a spreadsheet (probably still in the files area) which shows the reduction in FWHM with etalons slightly off-set to each other. Such an arrangement of, say, double 0.7A etalons does indeed give a FWHM of around 0.4A. The intensity peak is reduced, so I suppose you could say there's a lower SNR.
Added: If you tilt the front element say 1 degree to push the "ghosts" from the FOV, this would, based on Bob's graphs, move the CWL towards the blue by 0.4A.
Not exactly 0.4. And if to take in to account the S/N decreasing, there will be no gain vs standard DS when both peaks are at the same WL.

I experimented a lot with all my etalons and always the best results were when both etalons transmission curves were coincide - when the image was maximally bright and contrasty.


Valery.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

I don't disagree....
"the best results were when both etalons transmission curves were coincide "
The question was, when one element is tilted (to remove ghosts), how do you get it and the other back "on-band"


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

Merlin66 wrote:I don't disagree....
"the best results were when both etalons transmission curves were coincide "
The question was, when one element is tilted (to remove ghosts), how do you get it and the other back "on-band"
The second etalon is typically designed so, that it come to the CWL H-a when it tilted enough to place the ghost out of
the main solar image. I do have such a pair of LS50 etalons - the main etalon does not require any tilt to come to the CWL H-a
(at my typical atmospheric pressure and temperature) and the second etalon when adjusted to the CWL places the ghost
sun image outside or main solar image. Of course, when used as an internal etalon it produce severe banding and sweet
spot is not round, but a band - right enough to cover my camera chip.


Valery.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

Ah....
You're using different etalons within the DS.....
What about the case when you use two identical etalons??? Same CWL and bandwidth?


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

Merlin66 wrote:Ah....
You're using different etalons within the DS.....
What about the case when you use two identical etalons??? Same CWL and bandwidth?

Then we need circular polarizator between the etalons, cause we can't get rid of the ghost or
we need to change the elevation (higher) - and then tilt the etalons slightly and in opposite directions.


Valery.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
Bob Yoesle
Almost There...
Almost There...
Posts: 994
Joined: Thu Mar 08, 2012 7:24 pm
Has thanked: 539 times
Been thanked: 807 times

Re: C8 + PST?

Post by Bob Yoesle »

What about the case when you use two identical etalons??? Same CWL and bandwidth?

...cause we can't get rid of the ghost or we need to change the elevation (higher) - and then tilt the etalons slightly and in opposite directions.
Hmmm. That's VERY interesting Valery.

Perhaps why despite my elevation with my two nearly identical etalons I'm rarely tilting the primary etalon when double stacking - since I can't actually tilt it in the opposite direction (it's been a long time since I've used it single stacked to know the tilt needed when used by itself). All I can do is leave it in the "flat" TMax position and apply the necessary tilt to the second etalon. Most of the time the second etalon requires only about 1 mm of opening at the thumb wheel of the TMax tilt to remove all ghost reflections from the field of view of a low power eyepiece. Since the TMax has a diameter of 135 mm, 1/135 = tan θ, and therefore θ = 1.3 degrees.

I've also wondered why despite my custom clocking adapter I always find the overall best clocking position is with the TMax tilt hinge plates oriented 180 degrees from each other...

When left in the ~ 1.3 degree tilt position I had used frequently for visual observing, I found my images showed a bit of contrast gradient, even thought this was difficult to see visually:
5-6-13 Ha full disk proc jpg sm 2.jpg
5-6-13 Ha full disk proc jpg sm 2.jpg (263.4 KiB) Viewed 4295 times
More recently for imaging I have taken to leaving the first ghost just off the CCD sensor for minimum tilt, and this does give better uniformity to the disk contrast:
3-11-14 Full Disk SM.jpg
3-11-14 Full Disk SM.jpg (269.81 KiB) Viewed 4295 times
I have PM'd a couple of people including Christian to see if they can look at my Jacquinot spot rationale and calculations -- I really would like to see how DSing affects this, especially because of the narrowed transmission profile over that of a nominally identical FWHM single stacked filter...


Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders
Goldendale Observatory
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

Bob,
I still can't get my head around the issue of the CWL shifting when the etalon is tilted (to remove ghosts)
With identical etalons surely this must lead to a situation where the CWL's are NOT coincident....
(I used the tune my external double stack to give maximum on band brightness, then effectively lock them together to form a "single" 0.4A bandwidth unit. To see the red and blue wings the whole assembly was tilted - the relative positions of the etalons being unchanged)


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
marktownley
Librarian
Librarian
Posts: 42270
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20424 times
Been thanked: 10243 times
Contact:

Re: C8 + PST?

Post by marktownley »

I think the premise here is wrong; there is no such thing as two identical etalons. They may be 'close' but they are not identical. 'Identical' etalons occur in a textbook and an equation but not in day to day use.


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!
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

Mark,
Yeah, but.....
A 1 degree ghost tilt (+/- 0.4A shift) is still a hellava shift...
To me it would mean that the etalon, by design, would have to have a CWL of at least +0.4/0.5A above Ha to allow ghost tilting back on band.


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Bob Yoesle
Almost There...
Almost There...
Posts: 994
Joined: Thu Mar 08, 2012 7:24 pm
Has thanked: 539 times
Been thanked: 807 times

Re: C8 + PST?

Post by Bob Yoesle »

I think the premise here is wrong; there is no such thing as two identical etalons. They may be 'close' but they are not identical. 'Identical' etalons occur in a textbook and an equation but not in day to day use.
Then add to the mix that each etalon is not heated identically in series, or held absolutely firm in a constraining cell, but 'floats' on a sponge-foam ring and is radially supported by buttons of silicone, and then add in some changing ambient temperatures from morning to afternoon, followed by changes in gravitational pulling as the scope tracks from horizon to horizon... you get the idea.


Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders
Goldendale Observatory
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

And the last and the most influent factor for air spaced etalons - a barometric pressure.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
Bob Yoesle
Almost There...
Almost There...
Posts: 994
Joined: Thu Mar 08, 2012 7:24 pm
Has thanked: 539 times
Been thanked: 807 times

Re: C8 + PST?

Post by Bob Yoesle »

Christian has now added a section on air spaced etalons with the calculation of the Jacquinot spot diameter:

http://www.astrosurf.com/viladrich/astr ... P-Coro.htm


Diagonally parked in a parallel universe.

Curiosity is the father of knowledge; uncertainty is the mother of wisdom.

Dark-Sky Defenders
Goldendale Observatory
User avatar
Valery
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 4059
Joined: Sun Nov 18, 2012 3:13 pm
Has thanked: 156 times
Been thanked: 893 times

Re: C8 + PST?

Post by Valery »

Bob Yoesle wrote:Christian has now added a section on air spaced etalons with the calculation of the Jacquinot spot diameter:

http://www.astrosurf.com/viladrich/astr ... P-Coro.htm
Thank you, Bob, for this useful link.

Valery.
Last edited by Valery on Mon Feb 02, 2015 8:25 pm, edited 1 time in total.


"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.
User avatar
swisswalter
Way More Fun to Share It!!
Way More Fun to Share It!!
Posts: 17948
Joined: Thu Feb 06, 2014 4:28 am
Location: Switzerland
Been thanked: 1 time
Contact:

Re: C8 + PST?

Post by swisswalter »

thanks Bob


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 ;)
User avatar
marktownley
Librarian
Librarian
Posts: 42270
Joined: Tue Oct 18, 2011 5:27 pm
Location: Brierley Hills, UK
Has thanked: 20424 times
Been thanked: 10243 times
Contact:

Re: C8 + PST?

Post by marktownley »

excellent indeed, thanks!


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!
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

Some great stuff being discussed here.
The etalon as we know is only part of the Ha filter system.
I think the ITF and final sorting (blocking) filter supress the etalon "wings"


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
User avatar
Merlin66
Librarian
Librarian
Posts: 3970
Joined: Tue Dec 13, 2011 1:23 pm
Location: Junortoun, Australia
Has thanked: 173 times
Been thanked: 615 times
Contact:

Re: C8 + PST?

Post by Merlin66 »

The final section:
""Here we assume we have an incident convergent beam with no field angle. This is the situation when using a F-P etalon in a telecentric system"
I don't think this is correct...
Even with an external mounted etalon, the field angle will be 0.25 degrees. We have seen from previous discussions that the telecentric lenses can change this field angle, but never to zero.


"Astronomical Spectroscopy - The Final Frontier" - to boldly go where few amateurs have gone before
https://groups.io/g/astronomicalspectroscopy  
http://astronomicalspectroscopy.com
"Astronomical Spectroscopy for Amateurs" and
"Imaging Sunlight - using a digital spectroheliograph" - Springer
Post Reply