Question about H-alpha double stacking

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Question about H-alpha double stacking

Post by Dennis »

Hi,
there is the known mod for the Quark to stack it with a afterward placed air spaced etalon (Lunt / pst). Mica and air spaced etalon are both together in the telecentric beam of the quark telecentric. Instead of using a air spaced etalon - would this also work for a "normal" filter with 1.2A that is not a etalon?
Tilt tuning again then i assume.

Thanks.


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Re: Question about H-alpha double stacking

Post by marktownley »

Yes, in theory.

A air spaced etalon is a lot cheaper than a GOOD ultra narrow band Ha filter


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Re: Question about H-alpha double stacking

Post by Dennis »

marktownley wrote: Wed Oct 04, 2023 7:58 pm Yes, in theory.

A air spaced etalon is a lot cheaper than a GOOD ultra narrow band Ha filter
Thanks Mark. Well.. it would be around 2k $ .. not so much more expensive then the air spaced etalon. Problem that i see with the Lunt 40mm is the lack of transmission. And the filter version would have 90% peak transmission.


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Re: Question about H-alpha double stacking

Post by marktownley »

This has kinda done the rounds before, with Marty and a few others exploring it. Never really went anywhere or took off. What filter are you thinking of?


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Re: Question about H-alpha double stacking

Post by Dennis »

I see, im getting more infos about it probably today. Its a relatively new one, this is from a news piece.
Attachments
1.PNG
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Re: Question about H-alpha double stacking

Post by christian viladrich »

Hi Dennis,

It does not matter whether the filter is an etalon or a dielectic (hardcoated or softcoated) filters.

Years ago, I did a test with a 0.9 A etalon :

http://astrosurf.com/viladrich/astro/in ... ast-2b.htm

And a 1.5 A dielectric filter (Barr Associates) :
http://astrosurf.com/viladrich/astro/in ... -tests.htm

Back then, I had no way to measure their actual FWHM.

What is important is :
- peak transmission (for exposure time). A hardcoated filter could be close to an airspaced etalon (about 60-80%), softcoated filters (Andover, EO) have peak transmission in the range of 35-45%),
- the number of cavities : usually with 1.5 A FWHM hardcoated filter, there is only one cavity. This is quite interesting Alluxa can make it as a two-cavity filters with still a 90% peak transmission. 2-cavity means the filter is equivalent to a double-stack 1.2 A filter, which is great.

I had a talk with Alluxa back then when they made the press release. Are you planning some sort of group order ? Price goes down with the number of units.

Just check with Alluxa:
- the uncertainties on the CWL : this is indeed the most important data. If you have to tilt the filter, then the FWHM increases very fast,
- the effective index of the filter :
- with a high index, you can tilt the filter and have a lower broadening of the FWHM,
-with a high index you have reduced broadening of the FWHM when using telecentric mount,
- with a high index, you have a larger sweet spot when using a collimated mount,
- the temperature coefficient (shift of CWL with temperature) : it is related to the material. BK7 has lower temperature coefficient, so you need less tilt when temperature changes,
- AR coating, hardcoated filters can have issues with reflexions,
- off-band blockage : the filter probably cut wavelength 100-200 nm arround Ha.


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Re: Question about H-alpha double stacking

Post by Dennis »

Hi Christian, thanks for the input. For now i have no plans of a group or single order since first i wanted to wait for the input of you experts. Im motivated to try this if feasable since i dont like the "weak signal imaging" with h-alpha, we all have limited seeing conditions so we want to make the best of it.
I asked at Alluxa some of the questions you mentioned and will let you know the outcome. Also i will ask them about the other questions you mentioned.

Off band blocking should be no problem since anyways behind a block filter.


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Re: Question about H-alpha double stacking

Post by christian viladrich »

BTW, as an additional information :
- the effective FWHM of a 1.1 A one-cavity filter with effective index of 1.6 would be 1.15 A in a telecentric beam at f/30,
- the effective FWHM of a 0.6 A air-spaced etalon (such as Lunt) would be 1.08 A in a telecentric beam at f/30,

So about the same. The outcome all depends on the actual FWHM of the filters.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

hello Christian!

I still have the Barr 1,5A.
So if you would have time to measure its real Halpha transmission....


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Re: Question about H-alpha double stacking

Post by Dennis »

christian viladrich wrote: Thu Oct 05, 2023 11:52 am BTW, as an additional information :
- the effective FWHM of a 1.1 A one-cavity filter with effective index of 1.6 would be 1.15 A in a telecentric beam at f/30,
- the effective FWHM of a 0.6 A air-spaced etalon (such as Lunt) would be 1.08 A in a telecentric beam at f/30,

So about the same. The outcome all depends on the actual FWHM of the filters.
Sent you a pm.


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Re: Question about H-alpha double stacking

Post by Dennis »

Ok, so i think i got now enough information about the filter to say that i want one. Im waiting to hear Christians opinion about it once he can reach back to me.
Some specs: The filter is a 2 cavity h-alpha filter, fwhm is 0.1nm (+/- 0.05nm). Transmission >90%
The CWL is at 656.4nm, so in the red wing of h-alpha. Operating temperatures are -10 - 60°C it has to be tilt tuned on band (656.3nm), so a tilting device is necessary.
To reach on band with normal conditions a tilt of 1.6° is necessary. My interpretations of simulation results sent by the vendor is that a tilt of this magnitude will have no big impact on transmission and only a small one on the fwhm. Good enough for double stacking our mica etalons i would say.
This filter also needs to be behind a (the already existing one from the etalon) blocking filter to work. The big advantage would be the high transmission and the 2 cavity design which will cause a much better selectivity of the h-alpha band then a single cavity one.

So i would say we wait to hear what Christian thinks about it and then anybody who is interested prepare for a group order in the upcoming weeks.
if we reach 10 people we get a big price reduction and we will be at aprox 1.8k $ for a 20mm version.

I will keep you updated.
Last edited by Dennis on Sat Oct 14, 2023 1:55 pm, edited 1 time in total.


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Re: Question about H-alpha double stacking

Post by KMH »

Interesting....
What would you use as a tilting device?

Kevin


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Re: Question about H-alpha double stacking

Post by Dennis »

KMH wrote: Fri Oct 13, 2023 6:47 pm Interesting....
What would you use as a tilting device?

Kevin
Good question, ideally something very simple like Sebastien posted here: viewtopic.php?t=42805
I reached out for the company that sold / made it but so far no answer yet.
In case of emergency i would start out with a newton ring tilter.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

inside the tilter, you can see the 1,5A Barr associates used by christian!

I clearly prefer Mica+air spaced etalon (lunt 35, lunt 40, lunt 50) than mica+hard coated 1,5A.
less interferences, still very very bright.

I stay on the frenquency for a group order, but for another project... not for DS.


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Re: Question about H-alpha double stacking

Post by Dennis »

Sebastien Lebouc wrote: Mon Oct 16, 2023 9:09 am inside the tilter, you can see the 1,5A Barr associates used by christian!

I clearly prefer Mica+air spaced etalon (lunt 35, lunt 40, lunt 50) than mica+hard coated 1,5A.
less interferences, still very very bright.

I stay on the frenquency for a group order, but for another project... not for DS.

Thanks for the input Sebastien,
my experience with the Quark + Lunt 40 mod was that the light flux decreased by a factor of 2-3. I dont know why this happens, the air spaced etalon should have a transmission of around 70-80%. Anyways i think that a 2 cavity solution + tilt tunable with only very little impact on performance is sth i definitive want to try. Could be even interesting for to use without the mica in front: BF-> telecentric -> ha-filter-> cam


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

We should ask Christian for the global transmission of mica+barr 1,5A set up. When we have made the tests in may 2019, christian took time to calculate the transmission.

for your tests, did you take off the ERF body?


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Re: Question about H-alpha double stacking

Post by Dennis »

Sebastien Lebouc wrote: Mon Oct 16, 2023 12:22 pm We should ask Christian for the global transmission of mica+barr 1,5A set up. When we have made the tests in may 2019, christian took time to calculate the transmission.

for your tests, did you take off the ERF body?
Knowing the transmission of the barr filter and the resulting transmission with the mica is useful to know, right.
Yes i took off the Lunt Erf glass during testing. I can imagine that by tilting the Lunt etalon on band i loose some transmission.
It basically works, but i need to increase gain levels a lot which means i need to stack lots of images compared to Quark alone. And as far as i understand ds in general results in a much dimmer image. So im just looking for an "upgrade" of this method for better s/n. New technology now available should deliver it.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

I clearly think the mica (quark) is the bad link in the chain.
It has less transmission than air spaced etalon. You are ready to pay 2k€ to improve it where you can do a DS lunt 40 for half the price (DS module is supposed to be less than 700 USD).
I have spent the week to compared my solarspectrum +one lunt 40 vs 2 lunt 40, or a combo lunt50/lunt40/lunt 35. At eye, the DS air spaced are clearly brighter (I may write too much...).
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Re: Question about H-alpha double stacking

Post by Dennis »

Sebastien Lebouc wrote: Mon Oct 16, 2023 6:12 pm I clearly think the mica (quark) is the bad link in the chain.
It has less transmission than air spaced etalon. You are ready to pay 2k€ to improve it where you can do a DS lunt 40 for half the price (DS module is supposed to be less than 700 USD).
I have spent the week to compared my solarspectrum +one lunt 40 vs 2 lunt 40, or a combo lunt50/lunt40/lunt 35. At eye, the DS air spaced are clearly brighter (I may write too much...).
If one day you travell to south east france, I would be pleased to show you my set up on roof top!
Oliver and Steffen came on summer, I had to use an electric stick to take them off the balcony...

Yes, the Quark is the weak link. You mean i could use 2 lunt 40 etalons in a telecentric beam instead?
It sounds interesting, but what are the downsides? Because i dont see many people doing this.

Thank you, sounds great and i keep it in mind. Until then i have to improve my french : )


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Re: Question about H-alpha double stacking

Post by pupak »

I tried quite a few combinations of different etalons. Quark with tilted LS40, Quark with PST, Quark with pressure LS80 , 2 x LS40, LS40 with LS80 and the problem is always a big attenuation in H-a combined with Quark, or little contrast with 2 x LS40 and others without Quark. A lot depends on the F telescope. Linchtneknecker 150/F24 at F48 works well with 2 x LS40's and a 20mm double blocking filter from Andover. Attenuation is very little and contrast is acceptable. But this combination does not work with another telescope at the same F. Why? I do not understand that. I have 4 Quarks. Two have significantly less attenuation in H-a and are well usable in combination with LS40. The other two have more than double the attenuation and are only usable at large apertures of 210-230mm, where there is more light. I think the Quark prominence has less attenuation in H-a and is better suited for DSII with LS40.


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Re: Question about H-alpha double stacking

Post by Dennis »

pupak wrote: Mon Oct 16, 2023 8:08 pm I tried quite a few combinations of different etalons. Quark with tilted LS40, Quark with PST, Quark with pressure LS80 , 2 x LS40, LS40 with LS80 and the problem is always a big attenuation in H-a combined with Quark, or little contrast with 2 x LS40 and others without Quark. A lot depends on the F telescope. Linchtneknecker 150/F24 at F48 works well with 2 x LS40's and a 20mm double blocking filter from Andover. Attenuation is very little and contrast is acceptable. But this combination does not work with another telescope at the same F. Why? I do not understand that. I have 4 Quarks. Two have significantly less attenuation in H-a and are well usable in combination with LS40. The other two have more than double the attenuation and are only usable at large apertures of 210-230mm, where there is more light. I think the Quark prominence has less attenuation in H-a and is better suited for DSII with LS40.

Very interesting, thanks for sharing your experience Petr.
This is pretty much why i want to try this way with the new hardcoated filter instead of a classic f-p filter. Theory says it doesnt need a super high f-ratio or low tilt to work good, which makes it much more flexible. If i can remain 90% of the brightness of my Quark then this will be enough for imaging with nearly no gain (imx462) and no sweetspot or unpracticable f-ratio. Even more important: no issues or discussions about uniformity anymore.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

20230906_164813.jpg
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double lunt 40 module in telecentric beam FD4O (native 250mm refractor F10x baader TZ4)
20231002_162832.jpg
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Solarspectrum+ one lunt 40 module on LZOS 152. telecentric beam
20231002_173411.jpg
20231002_173411.jpg (2.19 MiB) Viewed 1691 times
double lunt40
By far the best set up, bright, absolutely no double limb visible, in visual you watch a solar processed picture.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

Draw back?
Heavy, long. I do not want to be a focuser at Seb's house...


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Re: Question about H-alpha double stacking

Post by Oak »

I have also been trying this but lots of reflections between the two lunt 40mm etalons and my view with quark+LS40 was superior to the tz4+LS40+LS40+b1200.

Where/what is the blocking filter in the double lunt 40 setup?
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Re: Question about H-alpha double stacking

Post by Dennis »

Impressive Sebastien, looks like a setup without compromises.
Derek: have you tried to add spacers between the etalons to get more distance between them?


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Re: Question about H-alpha double stacking

Post by Oak »

Dennis wrote: Tue Oct 17, 2023 5:34 pm Impressive Sebastien, looks like a setup without compromises.
Derek: have you tried to add spacers between the etalons to get more distance between them?
Not yet although that is next on the list. Perhaps put one etalon on each side of the blocker. I did try a circular polarizer and that darkened the image a bit too much for my liking.


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Re: Question about H-alpha double stacking

Post by EdAstle »

These photos of working equipment are invaluable. Thank you all!
I wish more would show off their equipment.
That sounds rude.

Baader: "circular polarising filters only work in one direction". I didn't know that.
I just bought a Baader Herschel and saw it in the online pdf manual.

I just bought a ton of stuff to learn from my own mistakes. Found this thread after purchases...

1. Altair D-ERF for my Skywatcher 150 f/8. Back in May when I started solar I thought no way am I paying £1k for a "filter". Now I regret not buying it sooner.
2. Lunt LS40THa + RAF Cam adapter. So impressed compared to my Quark Chromo. So I bought...
3. Another Lunt LS40THa + RAFCam adapter :-)
4. Baader TZ-4S to bring it all together

After spending "several k" I was swearing at myself for forgetting to spend a few quid on T2 extensions to get the stuff into focus.
Only 30 mins of trial, and all error I'm afraid. No sun since.

Alas the new Shell petrol station right by me is about 5 feet higher than it previously was, so my garden will be without sunlight until next year. Meh. I'm thinking of buying a scissor lift :-)

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Please keep those photos of your rigs coming. A picture is worth a thousand words!


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Re: Question about H-alpha double stacking

Post by Dennis »

Maybe an additional info: As far as i understand, the pricing is in a way that once we would reach 10 people we would basically get another filter on top for the same price (~2000$), since from 20 pieces price will drop from ~2K$ to ~1K$ per filter.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

To avoid ghost images, I have found some rules:
spacing the 2 etalons as much as possible
I use 30mm BF30 isle of man. if I put it at the end just before eyepieces, I have reflections. If I use a binoviewer, the long path avoids most of reflections
So I put the BF 30 between the two lunt40 modules.
Oliver Smie from Beloptik has adviced me to present the back side of air etalon (Red ERF filter toward eyepiece, not toward sun). I have tried, no more or less reflexions. It may be usufull for other air etalon.

So we have to deal with distance, positions and directions of lunt40( back to back, back to head, head to head). Rotation can increase or decrease contrast and brightness too.
with all these parameters, you can spend a complete sunny week-end to achieve a satisfying set up.... :lol:


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Re: Question about H-alpha double stacking

Post by Oak »

Sebastien Lebouc wrote: Wed Oct 18, 2023 6:46 pm To avoid ghost images, I have found some rules:
spacing the 2 etalons as much as possible
I use 30mm BF30 isle of man. if I put it at the end just before eyepieces, I have reflections. If I use a binoviewer, the long path avoids most of reflections
So I put the BF 30 between the two lunt40 modules.
Oliver Smie from Beloptik has adviced me to present the back side of air etalon (Red ERF filter toward eyepiece, not toward sun). I have tried, no more or less reflexions. It may be usufull for other air etalon.

So we have to deal with distance, positions and directions of lunt40( back to back, back to head, head to head). Rotation can increase or decrease contrast and brightness too.
with all these parameters, you can spend a complete sunny week-end to achieve a satisfying set up.... :lol:
Yes, lots of permutations to try! Hope I will get it sorted before winter. Last time out I started trying to use a collimated beam (as opposed to telecentric) and playing with that took up much of my time.


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Re: Question about H-alpha double stacking

Post by antonello »

KMH wrote: Fri Oct 13, 2023 6:47 pm Interesting....
What would you use as a tilting device?
Kevin
See this, if it helps
viewtopic.php?p=156165#p156165


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Re: Question about H-alpha double stacking

Post by Dennis »

antonello wrote: Thu Oct 26, 2023 10:46 pm
KMH wrote: Fri Oct 13, 2023 6:47 pm Interesting....
What would you use as a tilting device?
Kevin
See this, if it helps
viewtopic.php?p=156165#p156165
This is a genious design Antonello, thanks for sharing.
Does it work well and precise for you?


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Re: Question about H-alpha double stacking

Post by antonello »

Yes, the functioning is perfect, precise and very sensitive (and also economical, if one has good manual dexterity: there is only the modest cost of the Baader ring and the small knob).
Soon I will test the insertion of the BF 1800 Lunt filter into this tilting. I think that the fine adjustment (instead of the fixed positioning at 2° in the diagonal) will bring an improvement in contrast.


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Re: Question about H-alpha double stacking

Post by Dennis »

antonello wrote: Fri Oct 27, 2023 2:11 pm Yes, the functioning is perfect, precise and very sensitive (and also economical, if one has good manual dexterity: there is only the modest cost of the Baader ring and the small knob).
Soon I will test the insertion of the BF 1800 Lunt filter into this tilting. I think that the fine adjustment (instead of the fixed positioning at 2° in the diagonal) will bring an improvement in contrast.
Nice to hear, i might adopt parts of the design for my own tilters im planning to have done in a machine shop.
What did you use as center part / filter holder, or was that selfmade too?

About tilt adjusting a BF.. idk, a BF transmission window should be wide enough to always be on band at 0° if protected from high temperatures.


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Re: Question about H-alpha double stacking

Post by antonello »

Dennis wrote: Fri Oct 27, 2023 3:13 pm
Nice to hear, i might adopt parts of the design for my own tilters im planning to have done in a machine shop.
What did you use as center part / filter holder, or was that selfmade too?
The central part is a simple self-built aluminum cylinder, turned and milled (also to insert the small magnet). The drawing is easy to do, depending on your filter. From the photographs it is clear how it is made, but if you need a drawing, give me the dimensions of your filter and I will make the drawing for you.
.
Dennis wrote: Fri Oct 27, 2023 3:13 pm About tilt adjusting a BF.. idk, a BF transmission window should be wide enough to always be on band at 0° if protected from high temperatures.
Sure, the BF transmission is rotation tolerant, but What matters is NOT the transmission window, but the contrast. The micrometric rotation of the filter BF (always close to 2°) allows the slight diffusions of light caused by reflections to be brought out of the field. With fixed inclination, this is not totally possible. The filter in the my tilting system is a BF Omega Optical filter (23 mm in diameter) paid about 100 dollars. I have three of this, one of which is a recent generation (different), but all three are excellent.
This filter, thanks to the possibility of micro-regulation, allows positioning in tilting in a particular angle to obtain maximum contrast. In summary, with the Omega Optical filter I get a wonderful black (or almost) sky behind the edge prominences.
Recently, I bought a BF 1800 Lunt (second hand, but new, practically never used) with the filter permanently fixed in his diagonal. This filter in Europe costs more than 2000 dollars (!). Well, after removed the IR Cut filter in the Lunt BF, which notoriously reduces contrast, I've compared the two filters several times and most of the time the Omega Optical's image it was better better (even than the BF600 that I already had). Only in excellent seeing conditions, the BF1800 Lunt filter showed an imperceptible increase in sharpness, absolutely not capable of justifying the difference of 2000 dollars). The evident difference (in favor of my filters Omega Optical) is that micro tilting allows the diffuse light to be eliminated from the field, while the Lunt, being fixed, shows the sky behind the protuberances not black, but dark red and therefore with less contrast.The only tilting of my etalon does not solve the problem and I have seen that to obtain the best contrast it is necessary to have the tiltinf of both the etalon and the BF. I have seen that micro adjustment of my tilting system is so sensitive as to allow super-fine rotation and I think that by putting the Lunt BF1800 in the tilting system I can also have with this filter the great contrast that I have with the Omega Optical filters.


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Re: Question about H-alpha double stacking

Post by Dennis »

antonello wrote: Fri Oct 27, 2023 6:46 pm
Dennis wrote: Fri Oct 27, 2023 3:13 pm
Nice to hear, i might adopt parts of the design for my own tilters im planning to have done in a machine shop.
What did you use as center part / filter holder, or was that selfmade too?
The central part is a simple self-built aluminum cylinder, turned and milled (also to insert the small magnet). The drawing is easy to do, depending on your filter. From the photographs it is clear how it is made, but if you need a drawing, give me the dimensions of your filter and I will make the drawing for you.
.
Dennis wrote: Fri Oct 27, 2023 3:13 pm About tilt adjusting a BF.. idk, a BF transmission window should be wide enough to always be on band at 0° if protected from high temperatures.
Sure, the BF transmission is rotation tolerant, but What matters is NOT the transmission window, but the contrast. The micrometric rotation of the filter BF (always close to 2°) allows the slight diffusions of light caused by reflections to be brought out of the field. With fixed inclination, this is not totally possible. The filter in the my tilting system is a BF Omega Optical filter (23 mm in diameter) paid about 100 dollars. I have three of this, one of which is a recent generation (different), but all three are excellent.
This filter, thanks to the possibility of micro-regulation, allows positioning in tilting in a particular angle to obtain maximum contrast. In summary, with the Omega Optical filter I get a wonderful black (or almost) sky behind the edge prominences.
Recently, I bought a BF 1800 Lunt (second hand, but new, practically never used) with the filter permanently fixed in his diagonal. This filter in Europe costs more than 2000 dollars (!). Well, after removed the IR Cut filter in the Lunt BF, which notoriously reduces contrast, I've compared the two filters several times and most of the time the Omega Optical's image it was better better (even than the BF600 that I already had). Only in excellent seeing conditions, the BF1800 Lunt filter showed an imperceptible increase in sharpness, absolutely not capable of justifying the difference of 2000 dollars). The evident difference (in favor of my filters Omega Optical) is that micro tilting allows the diffuse light to be eliminated from the field, while the Lunt, being fixed, shows the sky behind the protuberances not black, but dark red and therefore with less contrast.The only tilting of my etalon does not solve the problem and I have seen that to obtain the best contrast it is necessary to have the tiltinf of both the etalon and the BF. I have seen that micro adjustment of my tilting system is so sensitive as to allow super-fine rotation and I think that by putting the Lunt BF1800 in the tilting system I can also have with this filter the great contrast that I have with the Omega Optical filters.

Valuable information, thanks. Yes its actually straight forward and clear how its made. Mainly it should use 1" sized filters, but i want to be able to use machined adapter rings for smaller filters like 20mm too. Already made a drawing for those, this are simple but delicate to machine parts(image), 2mm thick.

edit: Actually the adapter rings are not necessary, i just saw that the filters can be ordered with custom sizable outside rings.


Now i see why you want to tilt adjust also the BF1800, didnt think of reflections, makes sense.
Last edited by Dennis on Mon Oct 30, 2023 12:32 pm, edited 1 time in total.


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Re: Question about H-alpha double stacking

Post by DavidP »

Sebastien. What do you have between your 2 Lunt 40s? Is it a tilter?
I’m also wondering about the distance between your TZ4 and the ultimate focal point. It looks longer than the specified 220mm.


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Re: Question about H-alpha double stacking

Post by Sebastien Lebouc »

Between, I have a coronado Isle of Man BF, in a very large 2" tilter.
So I have 3 ways of tilting!

The device is very long, distance is very longer than the 220mm,but it works perfectely. Absolutely no double limbe, the photosphere is completly vanished.
I have a solarspectrum 0,45A with TZ at good distance, I can see the double limb effect. also on a 6000USD 0,4PE daystar. With 2x 600USD lunt 40 and a BF, I get perfect images, constrasted, bright, at least 2 times the optimized distance....


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