PST etalon (or similar) in a telecentric beam

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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

What sort of usable field of view can you get out of the SCT system Frederic?


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

fjabet wrote:
Valery wrote:OK, can you be more specific with your expectations in each of these cases - #3 and #5? And how have you measured them?


Thanks,

Valery.
I don't have a HR spectrophotometer. Nevertheless the PST etalon behaves like in its nominal full PST outfit, and by the way this one is very good, it is close to a single stack Coronado SM front filter. I use it also for imaging with the HaT and it is better than my Quantum for this application.

In the case of the Lunt it was Oliver's set up and the result was pretty much the same as my Quantum.
If there any chances you show us the photos you take with this PST etalon in it's normal configuration (say with refractor F/10) and with SCT Ha?
Also the pictures through LS50F Ha + SCT Ha ?

Thanks,

Valery.


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Re: PST etalon (or similar) in a telecentric beam

Post by mdwmark »

Hi Guys,
You missing why they don't use a telecentric beam on a air spaced etalon.
If you started out with a .5Ang air spaced etalon and put it in a F/30 telecentric the etalon would broaden out to about 1.2 Ang.
It will be uniform but much broader.
Like stated earlier, It,s the same bandwidth just the wavelength shifts from the center blue from all sides, and you get your sweet spot.
When designing the collimated lens. You should get one of those free lens programs to play with for your spacing. If you just put a -300mm lens in front of prime focus you will find that you need the thickness of the lens. And the back lens spacing is important too. And the direction the lens are facing makes a big difference. It can take you from 1/4 wave to over 1 wave just by the direction the lens are facing.
Unless you are going to be around F/70 with an air spaced etalon your are going to have to live with a sweet spot.
Remember the broader the filter the smaller the sweet spot.
Mark W.


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

marktownley wrote:What sort of usable field of view can you get out of the SCT system Frederic?
That depends on your etalon size.
With a 50mm etalon and without the SCT thread that limits to 44mm clear aperture, the system delivers the full sun. But you would need a focal reducer + a long FL eyepiece. It's possible, but I don't see the point. But you could use a full frame sensor.
With a Quantum (32mm diameter), I see 1/5 of the solar surface with a 35mm Eudiascopic or a XW30. I use this configuration with a CMOSIS CMV4000 (11,2mm square sensor) and with a Meade 6.3 reducer when the seeing is very bad.
With a 20mm PST + BF15, the field just fill up the 35mm Eudiscopique. But with the binovue the AFOV limitation isn't an issue.


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

mdwmark wrote:Hi Guys,
You missing why they don't use a telecentric beam on a air spaced etalon.
If you started out with a .5Ang air spaced etalon and put it in a F/30 telecentric the etalon would broaden out to about 1.2 Ang.
It will be uniform but much broader.
Like stated earlier, It,s the same bandwidth just the wavelength shifts from the center blue from all sides, and you get your sweet spot.
When designing the collimated lens. You should get one of those free lens programs to play with for your spacing. If you just put a -300mm lens in front of prime focus you will find that you need the thickness of the lens. And the back lens spacing is important too. And the direction the lens are facing makes a big difference. It can take you from 1/4 wave to over 1 wave just by the direction the lens are facing.
Unless you are going to be around F/70 with an air spaced etalon your are going to have to live with a sweet spot.
Remember the broader the filter the smaller the sweet spot.
Mark W.
Hi Mark,

I believe that the narrower the filter, the smaller the sweet spot.

I also don't believe that any of these air spaced etalons mentioned (PST and LS50) work fine because all air spaced etalons
are MUCH more sensitive to converging of the beam that the solid spaced etalons. Where the solid spaced etalons will work fine
with about F/30, all air spaced etalons will fail.
Walter Koch already tried the telecentric baader (TZ4) with his LS50F Ha with fail.

This is the reason why Lunt Engineering use a collimation - refocusing system in their telescopes with internal etalons.


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Valery wrote:
If there any chances you show us the photos you take with this PST etalon in it's normal configuration (say with refractor F/10) and with SCT Ha?
Also the pictures through LS50F Ha + SCT Ha ?

Thanks,

Valery.
On this link, the first one is PST DS, the second a single PST. The seeing was very poor and there are some fringes.
http://www.astrosurf.com/ubb/Forum3/HTML/041024.html
I didn't take any image with the PST in its standard configuration.

The LS50F + HaT test has been done in Serbannes with Oliver's filter, I didn't have the time to take any image. But we had a very nice view in it with Oliver and Christian Viladrich. If Oliver passes by, he would comment.
I ordered a LS50FHa and I will test that has soon as I receive it and I have the adaptation rings done.
If the Lunt is good (i.e. if I'm lucky), there will be a Quantum 0.6 PE in the classified soon...


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Valery wrote:
Hi Mark,

I believe that the narrower the filter, the smaller the sweet spot.

I also don't believe that any of these air spaced etalons mentioned (PST and LS50) work fine because all air spaced etalons
are MUCH more sensitive to converging of the beam that the solid spaced etalons. Where the solid spaced etalons will work fine
with about F/30, all air spaced etalons will fail.
Walter Koch already tried the telecentric baader (TZ4) with his LS50F Ha with fail.

This is the reason why Lunt Engineering use a collimation - refocusing system in their telescopes with internal etalons.


Valery.
In theory you're right, but if the telecentricity is very good it just works. The bandwidth may be a bit broadened, but I just can't tell the difference.
Jean Pierre also used his LS35 etalon with his 230mm in a telecentric configuration with success.

And the great advantage on the collimated solution is that there is no soft spot as there is just the marginal angle and no field angle.


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Here is a better one with the PST single stack.
Image


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

Thanks for the info guys! :)


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Re: PST etalon (or similar) in a telecentric beam

Post by swisswalter »

fjabet wrote:Here is a better one with the PST single stack.
Image
hi Frédéric

what a teriffic shot


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

mdwmark wrote:It,s the same bandwidth just the wavelength shifts from the center blue from all sides, and you get your sweet spot.
Hi Mark, Frederic et al,

I don't know if anyone can answer this, but as the wavelength shifts from the centre to blue at the edges does it do it in a linear way, or does it do it non linearly? i.e. the further you get from the centre the more progressively blue it becomes - kind of like with the inverse square law and how gravity falls away with distance...


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Intuivively, I would say a sine law ?


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

fjabet wrote:
Valery wrote:

And the great advantage on the collimated solution is that there is no soft spot as there is just the marginal angle and no field angle.
Frederic,

All depends. Have you seen my photos here? They all were made with the telescope equipped with a specifically designed collimation system.
Also, look at photos taken with Lunt dedicated solar telescopes (with internal collimated system)?

Have you seen soft spot on them?


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

I agree, there is no soft spot if the etalon is large enough to keep the field angle below 0.5°. But with a FL long enough to aim at high resolution, the telecentric seems to me the best way to go : I prefer to have only some controlable marginal angle than field angle and a non homogeneous bandpass over the FOV. I'm using quite large sensors for imaging (CMOSIS CMV4000, and the IMX174 pretty soon), sometimes with a focal reducer, so I'm very concerned with the field consistancy.
BTW I've seen in a quite large number of Lunt with internal etalon, and I've not been thrilled by the result. I've found the quality very inconstant, including a pair of LS152 with the field not being on band completly.

I think that Lunt and Coronado have chosen the collimated path to preserve a short FL and the capability to see the full disk and not because it's better than the telecentric solution.


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Just another advantage of the telecentric solution : you can use a mirror telescope. With the internal collimated etalon I'm not sure it's possible (unless having a huge baffle to place the etalon in). And over 200mm aperture a refractor is clumsy and more expensive.
Now for smaller intruments you may be right, the collimated option has advantages starting with the shorter FL.
I thought all this in a >200mm perspective. Actually my next project is a 350mm aperture Ha+CaK telescope (not a C14, that's a completly different design from the HaT and a SCT couldn't cope with UV bandwidth).


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

fjabet wrote:I think that Lunt and Coronado have chosen the collimated path to preserve a short FL and the capability to see the full disk and not because it's better than the telecentric solution.
I completely agree Frederic


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

fjabet wrote:I agree, there is no soft spot if the etalon is large enough to keep the field angle below 0.5°.
How do we do this with a PST mod and a collimating lens system, or is it just not possible with the small size of the PST etalon?


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Hello Mark,

as a rule of the thumb, the chief ray field angle for a 0,25° field (full sun) is -0,25*F/f in degrees where F is the refractor FL, and f the negative lens FL.
For example for the PST : -0,25*400/-200 = 0,5° => we are within the etalon tolerance (that is less than 0,5° in the case of a collimated beam, the telecentric solution is 2x more tolerant regarding the angles as mentionned in a paper I've seen some times ago).
If you want this for a 100/1000 refractor, then you must increase the negative lens to -500mm. In that case, to keep the F/10 ratio, the negative element aperture must be (-)500/10 = 50mm. Thus you need a 50mm etalon as well. And the etalon should be quite deeply installed in the refractor.
In fact the real issue with this is to find the negative lens, they are scarcer than converging lenses in manufacturer portfolio.
But with a 100/1000 refractor and a 50mm non obstructed etalon, you have a home brewed Lunt 100 :)


Frédéric.


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

fjabet wrote: If you want this for a 100/1000 refractor, then you must increase the negative lens to -500mm. In that case, to keep the F/10 ratio, the negative element aperture must be (-)500/10 = 50mm. Thus you need a 50mm etalon as well. And the etalon should be quite deeply installed in the refractor.
He don't need to go with 100mm F/10 refractor. He can go with 100mm F/5.


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

fjabet wrote:
I think that Lunt and Coronado have chosen the collimated path to preserve a short FL and the capability to see the full disk and not because it's better than the telecentric solution.
It is indeed better than telecentric solution if an etalon is air spaced. Lunt did his job nicely with no mistakes. In the same time I know two cases when Lunt airspaced etalons were used in a telecentric configuration. Both failed due to lowering of the contrast (bandpass broadeing).

Valery.
Last edited by Valery on Sat Aug 16, 2014 1:08 pm, edited 2 times in total.


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

Valery wrote:He don't need to go with 100mm F/10 refractor. He can go with 100mm F/5.
Yes, that's another way of doing it...


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

I wonder if the field angles increasing as the FL shortens ?

Anyhow as I said the collimated beam preserves the FL and maybe the way to go for aperture <180mm. But for larger telescope, you don't really have a choice and you don't want to make full sun but rather high resolution.

As for Lunt performances, we are several observers who don't share you enthousiasm but maybe we have been unlucky :)

Do you have any specs and picture of your commercial system ?


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

fjabet wrote:I

As for Lunt performances, we are several observers who don't share you enthousiasm but maybe we have been unlucky :)

Do you have any specs and picture of your commercial system ?
Yes, definitely, you, guys, were extremely unlucky because all of you own bad Lunt scopes(???). First - why not ask Lunt to replace the telescopes of fix the problems? They seems to have excellent customer service. Secondly, what are real problems with all your, guys, Lunt telescopes with collimated internal etalons?
What the telescopes you were unhappy with?

BTW. I wan't share any details about my commercial products. Hope this understandable.


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Re: PST etalon (or similar) in a telecentric beam

Post by fjabet »

Let us say that a lot of the Lunt I've seen on the field were below expectations in term of contrast and/or uniformity. I know very well a LS152 that just can't show more than 40% of the field on band.
Now it seems that there was (is?) an issue with the Lunt BF as replacing it with a Coronado would increase the contrast.

Anyway we will have to use Lunt now as Coronado is gone, at least for a while...

I was not asking for your design, but just the commercial product presentation...


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

fjabet wrote:Let us say that a lot of the Lunt I've seen on the field were below expectations in term of contrast and/or uniformity. I know very well a LS152 that just can't show more than 40% of the field on band.
Now it seems that there was (is?) an issue with the Lunt BF as replacing it with a Coronado would increase the contrast.

Anyway we will have to use Lunt now as Coronado is gone, at least for a while...

I was not asking for your design, but just the commercial product presentation...

Andy Lunt himself has said that his LS152T is purposed for high resolution views and imaging.
Such a telescope is not for full disk viewing - there are a lot of alternatives in smaller sizes - 50mm, 60mm, 80mm and 100mm size - with front mounted and with internally mounted etalons. However even with LS152T our friend Pedro easily imaging the Sun in full disk size. Same with several other owners of LS152T.
If correctly adjusted, LS152 shows full sun disk in Ha, may be with some contrast loss near the edge of the sun disk. I saw enough photos where all is OK with sun disk in band. More so, I can tell you, that my solar kit has been designed for using in 100mm F/5, 120mm F/5 and 150mm F/5 telescopes.

More developments will follow soon.


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

I rediscovered this topic having a read around on grey winters day.

I have a TZ4 now (after saying a year ago I was going to get one!), I've got a couple of experiments I want to try with it on my ED80 refractor, first off the PST etalon on it, secondly the Quark on it (minus it's native telecentric and blocker and with new, larger blocker fitted), and thirdly the PST etalon and Quark on it in stacked configuration. Don't expect anything quick in terms of results - mid february at the earliest, and that is with good weather - mid winter now with the sun at it's lowest. Plus I need to expand my collection of T-thread adapters for maximum connectivity options.

Over a year on, and maybe a little wiser(?), we talk about 2 types of etalons - air spaced, the Coronado and Lunts, and solid etalons, the Daystar and Solar Spectrums. However I wonder realistically if the first type can be divided down into 2 sub categories - Those designed to sit on the front of a scope infront of an objective and those designed to be used in a collimated optical setup - basically external and internal. I also wonder how these are designed differently? We talked earlier about a 0.5a air spaced (eg PST etalon) running in an f30 telecentric beam and said that it would be effectively working at 1.2a, but when you look at the shots Frederic is getting with the 8" HaT and PST etalon in an f27.8 telecentric they certainly look a lot more contrasty than what a 1.2a bandpass would give.

I wonder how sensitive etalon performance is in situations like this to 'perfect' telecentricity? In other words like with the 8" HaT where you have a telecentric designed bespoke for the optical system (8" Edge HD) then you would expect to get 100% perfect results as this is what you are designed for. However, say with the TZ4 on the back of a (random) refractor, say my ED80 for example, you get less than perfect telecentricity but still a reasonable result, maybe analogous to the quark - where people use the same telecentric system on a wide variety of scopes and focal ratios, it works to a point but only sub optimally (we don't know what optical configuration the telecentric on the quark was designed for). Then maybe a step further and take the example of a Televue Powermate, allegedly telecentric and used widely with daystar filters on a wide variety of optical configurations of scopes, maybe we're only getting a fraction of the performance we could with this setup?


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

I guess it's appropriate to include a link to this - very relevant http://www.cloudynights.com/topic/48759 ... t-filters/


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

Thanks, Mark, for your info.



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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

Thanks Valery, yes, the more experiences we have of these etalons and combinations the better :)


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Re: PST etalon (or similar) in a telecentric beam

Post by GreatAttractor »

Valery wrote: I found that my BF10 Coronado is absolutely the best blocker I ever used. It is 3x brighter and a bit more contrasty that two my Lunt B1200 and 5x brighter than Lunt B1800.
Valery,
Interesting, perhaps I will take a BF10 instead of a Lunt B1200 when I'll be replacing my B600. Can you unscrew the eyepiece holder and 1.25" nosepiece from the diagonal? Does it have T2 threads underneath like Lunt diagonals?


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

GreatAttractor wrote:Can you unscrew the eyepiece holder and 1.25" nosepiece from the diagonal? Does it have T2 threads underneath like Lunt diagonals?
On mine with a bit of force initially to break the threadlock which Coronado seems to like using it will come apart, but i'm fairly certain it's not T2, not sure what it is without measuring. Should be easy enough to make an adapter though.


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Re: PST etalon (or similar) in a telecentric beam

Post by solarmax2016 »

I have a PST MOD on my Meade 102ED that produces good images in the range of a .4 to .5 Angstrom quality Etalon.
Looking at the recent comments on discarding the front and rear collimators, I erroneously tried inserting a Losmandy
Telecentric lens in front of the front collimator lens which of course did not work. The idea of removing the front and
back collimators and substituting the Losmany Telecentric only sounds sensible. In making the PST MOD to suit my
demands I machined its entire optical unit in Anodizing grade aluminum which I anodized bright black. Integral
focus was achieved with a Lunt variable focuser. It takes either a Lunt 12 mm Blocker in diagonal or straight-through
Lunt 12 mm blocker focusing perfectly. The minus 200 focal length required by the PST etalon places a 2" nosepiece
at 1-1/2 inch length right up against the Meade 102 focuser racked in as far as it goes. The Meade 102 was made for
this application with a very long focal outreach. The unique thing about the Losmandy Telecentric is that its 2" barrel
fits right into a regular focuser and its rear threads are in a T-thread, so only a T-thread adapter to the 50 mm Metric
are required to fit into the front PST Etalon. That thread is what machinists call a difficult thread to cut - substituting
either a 42 or 46 British Thread to substitute for it. It cost me well over $150.00 to make this rig . Comments?


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Re: PST etalon (or similar) in a telecentric beam

Post by Valery »

Very interesing.
Last edited by Valery on Tue Feb 06, 2018 3:54 am, edited 1 time in total.


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Re: PST etalon (or similar) in a telecentric beam

Post by Galosimo »

I read your discussion and I wanted to share with you but experience. I apologize but I use the translator. I use a successful hack as previous therad, 152/900 that before I replaced the pst front lens with a -120 for my reach, then still not happy because there was still the sweet spo very visible I did do a telecentric 5 x own for my focal of 900. Now I have the image completely in h-alpha without sweet spot I mounted a BF15 and wait to find a second .pst to double the bandwidth. I also modified by the addition of an h-alpha omega optical filter placed before or after the telecentric which greatly improves the contrast. plus I added a tube to the telescope to avoid the big rush and I assure you that the image is excellent.


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Re: PST etalon (or similar) in a telecentric beam

Post by Galosimo »

Versione 1.jpg
Versione 1.jpg (90.62 KiB) Viewed 5472 times
Versione 2.jpg
Versione 2.jpg (74.74 KiB) Viewed 5472 times
It is very well known extension


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Re: PST etalon (or similar) in a telecentric beam

Post by Galosimo »

I used this a h-alpha filter:
http://www.ebay.com/itm/Optical-Interfe ... 1670196736
the light fades slightly but the filter must use with t2 tilting.
The telecentric system is hidden inside the tube, and this week I build a tilting to erf that menterò the wire of the telescope where it starts that particular flange then I will have a tilting to erf very convenient. I look only to find the second pst to add the x doblestuck.


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Re: PST etalon (or similar) in a telecentric beam

Post by marktownley »

Some nice mods there!


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