Effect of blocking filter position on bandwidth.

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Effect of blocking filter position on bandwidth.

Post by pupak »

I recommend a simple experiment to everyone. If your setup allows, place a blocking filter in the collimated beam behind the etalon. Both the Quark filter 25mm and the B1200 show an effect on the overall bandwidth reduction in the single etalon system. Especially B1200 in a collimated beam gives almost the same result as DSII. The disadvantage is vignetting for a chip larger than 12 mm. I got the best results with the TZ3 and TZ4. I feel that even for a blocking filter, a perpendicular beam is ideal. I wonder if others will confirm what I happened to discover.


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Re: Effect of blocking filter position on bandwidth.

Post by Rusted »

Forgive me for asking, but where else can a blocking filter go other than behind the etalon?

The addition of a TZ3 or TZ4, in front of the blocking filter, should further decrease any variation from parallelism of the beam.

The addition of diverging optics after the blocking filter will only affect the relative size of the sweet spot on the sensor as well as image scale.

Those of us using an F/10 objective with an [F7] Lunt etalon will not only be feeding our etalons on a diverging beam but we will not be feeding parallel light to our blocking filters.

Does this mean we all have to start saving up for a TZ3 or TZ4?


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Re: Effect of blocking filter position on bandwidth.

Post by Carbon60 »

Interesting. I’ve also noticed that the alignment of the BF is important. If the BF is not mounted perpendicular to the axis of the light cone, then it can result in banding across the disk. Sloppy connections, or droop between the etalons and BF, can lead to this effect.

Stu.


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Re: Effect of blocking filter position on bandwidth.

Post by pupak »

Rusted wrote: Thu Feb 02, 2023 7:23 am Forgive me for asking, but where else can a blocking filter go other than behind the etalon?

The addition of a TZ3 or TZ4, in front of the blocking filter, should further decrease any variation from parallelism of the beam.

The addition of diverging optics after the blocking filter will only affect the relative size of the sweet spot on the sensor as well as image scale.

Those of us using an F/10 objective with an [F7] Lunt etalon will not only be feeding our etalons on a diverging beam but we will not be feeding parallel light to our blocking filters.

Does this mean we all have to start saving up for a TZ3 or TZ4?
For example, the classic Quark has a BF before the etalon at the input of the telecentric term. All LUNT telescopes have a BF in a conical beam behind the etalon. It is not important if the BF is before or behind the etalon, but if it is in the collimated beam. While I only had the BF1200, I did the same thing to prevent vignetting, but once I accidentally changed the order of the elements and the result surprised me with a huge increase in contrast, unfortunately at the cost of vignetting on the 17mm camera chip.
I bought a camera with an 11.6mm chip and am looking forward to further experiments with the BF position in the system. Quark's BF also shows contrast improvement, but not as much as Lunta's BF. This is probably due to its higher bandwidth.
My feeling is that the BF in the collimated beam also acts like a DSII and narrows the resulting bandwidth. I'm waiting for the sun to experiment, but those of you who have it can try now.
Only those who have etalon without collimating lenses can try. The second option is to place the BF at the output of the TV5x PMT, or the TV4xPMT behind the pressure etalon with lenses. This works too, but at the cost of a large focal length.
It is ideal with a TZ and a naked etalon.
There are certainly many experienced people here who can give a qualified opinion on this topic.
(sorry for my Google English)


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Re: Effect of blocking filter position on bandwidth.

Post by Rusted »

Thank you for the thorough explanation. :bow


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Re: Effect of blocking filter position on bandwidth.

Post by MAURITS »

Interesting 🤔


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Hi

Are you talking about a PST or Lunt internal etalon set up with a collimating lens before the etalon and a re-focussing lens after the etalon. And you are seperating the re-focus lens from the supplied module in order to fit a selection/trim/blocking filter in the collimated beam coming out of the etalon and before the re-focus lens? The collimated beam is phase coded so a smaller aperture filter will do funny things to the image.

Cheers. Andrew.


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Hi

I am confused by you talking about a collimated beam system like the PST or LUNT70 and then a Baader TZ that would be used in telecentric system before an etalon.

Can you show some pictures of your set up please.

Cheers. Andrew.


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Rusted wrote: Thu Feb 02, 2023 7:23 am Forgive me for asking, but where else can a blocking filter go other than behind the etalon?

The addition of a TZ3 or TZ4, in front of the blocking filter, should further decrease any variation from parallelism of the beam.

The addition of diverging optics after the blocking filter will only affect the relative size of the sweet spot on the sensor as well as image scale.

Those of us using an F/10 objective with an [F7] Lunt etalon will not only be feeding our etalons on a diverging beam but we will not be feeding parallel light to our blocking filters.

Does this mean we all have to start saving up for a TZ3 or TZ4?
HI

On a Daystar Quark the trim filter / combined energy reflection, blocking filter is before the 4.2x telecentric or combo unit before the etalon.

On a PST the small trim filter is after the prism with a energy rejection filter in front of the etalon?

If you are using a F10 lens in front of a Lunt etalon should you not be using suitable collimating and re-focus lenses to get a parrallel beam through the etalon, just as in a PST not used at F10? Unless you are happy to vignette a shorter fl scope to F10 for a PST and to F7 for a Lunt?

I am confused by the reference to a Baader TZ in the context of a LUNT F7 collimated beam etalon.

Further.

Ah. The Lunt lenses are removed and the Baader TZ used so the etalon is now in a telecentric setup and the trim/blocking filter is vignetting the magnified solar image.

Rather than in the Daystar Quark where its in the front of the native tele-centric beam 4.2x or your own telecentric-Combo, before focus.

Andrew.
Last edited by AndiesHandyHandies on Thu Feb 02, 2023 11:41 pm, edited 1 time in total.


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Carbon60 wrote: Thu Feb 02, 2023 7:28 am Interesting. I’ve also noticed that the alignment of the BF is important. If the BF is not mounted perpendicular to the axis of the light cone, then it can result in banding across the disk. Sloppy connections, or droop between the etalons and BF, can lead to this effect.

Stu.
HI

CV notes the components of a solar telescope need to be within 1degree perpendicular to the optical axis to get best contrast in the image.

Cheers. Andrew.


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Re: Effect of blocking filter position on bandwidth.

Post by pupak »

AndiesHandyHandies wrote: Thu Feb 02, 2023 10:54 pm Hi

I am confused by you talking about a collimated beam system like the PST or LUNT70 and then a Baader TZ that would be used in telecentric system before an etalon.

Can you show some pictures of your set up please.

Cheers. Andrew.
I use the Baader TZ3 and TZ4 basically with naked etalon without collimating lenses, Quark combo, or Lunt 40. Behind the etalon is the BF from Quark. This combination is for the AR150/F6, AR150/F8 and AR90 F10.
Another set is an AR150 / F6 and an AR150 / F8 with a Lunt LS80 etalon for the F7. Behind him is TV 4X PMT, or TV 5x PMT, then Quark and BF.
I never combine LS80 and TZ. It wouldn't make sense.
I'm trying different combinations of etalons and BF and looking for the optimal setting. I am also going to test two etalons from PST, but for now I am dealing with their modification, because they do not work well.
But in this thread I write about the effect of LUNT's BF placement on the resulting bandwidth, which is a slightly different topic.


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Re: Effect of blocking filter position on bandwidth.

Post by Rusted »

Thank you for your patience in expanding on your aims and to Andrew for teasing out more detail.

The F7 Lunt 60 etalon is pressure tuned so unable to perform "naked."
The collimation lenses are sealing the system. So their removal would destroy the ability to tune in the H-a band.

Those of us who invested in quality f/10 optics, for their PST mods, now find themselves at a disadvantage with Lunt's PT f7 modular etalons.
A weak positive lens added before the Lunt PT etalon would solve the problem.
Nobody has suggested a suitable lens so far. My own presumption is a quality, long focus achromat.
Of a minimum 40mm aperture to avoid vignetting. To convert f/10 to f/7 within the converging beam.

I haven't discovered a formula for calculating the required power of this lens at a suitable position.
An achromat may not even be necessary for monochromatic H-a use but opens up the possibility of using a small refractor objective.
Such lenses are intended for parallel light. So may be slightly "unhappy" working within a converging beam.

My apologies if I am drifting too far off the original topic.


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Re: Effect of blocking filter position on bandwidth.

Post by marktownley »

Mounting any (ultra) narrowband image in a telecentric beam will have the effect of it having a tighter bandpass and reducing parasitic continuum leakag. This isn't necessarily from the off band comb peaks from the etalon but from scatter.

I do the same with my hi-res cak setup.


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Re: Effect of blocking filter position on bandwidth.

Post by pupak »

Rusted wrote: Fri Feb 03, 2023 6:31 am Thank you for your patience in expanding on your aims and to Andrew for teasing out more detail.

The F7 Lunt 60 etalon is pressure tuned so unable to perform "naked."
The collimation lenses are sealing the system. So their removal would destroy the ability to tune in the H-a band.

Those of us who invested in quality f/10 optics, for their PST mods, now find themselves at a disadvantage with Lunt's PT f7 modular etalons.
A weak positive lens added before the Lunt PT etalon would solve the problem.
Nobody has suggested a suitable lens so far. My own presumption is a quality, long focus achromat.
Of a minimum 40mm aperture to avoid vignetting. To convert f/10 to f/7 within the converging beam.

I haven't discovered a formula for calculating the required power of this lens at a suitable position.
An achromat may not even be necessary for monochromatic H-a use but opens up the possibility of using a small refractor objective.
Such lenses are intended for parallel light. So may be slightly "unhappy" working within a converging beam.

My apologies if I am drifting too far off the original topic.
I have tried to change the optical properties of the LS80 collimating lens with no success. On the contrary, I found that the LS80 for F7 has no problem on the AR90/F10 if it is correctly positioned relative to the focal length of the lens. The simulation clearly shows that in the correct position the etalon has a collimated beam. The problem can be the small diameter of the etalon compared to the aperture of the telescope. This was shown when trying to use the LS80 with a 200mm Triband.
For LUNT pressure etalons, the collimating lenses must be replaced with plane-parallel glass to maintain chamber tightness. Unfortunately, I have no idea where to buy such glasses.
Etalons and BF provide huge room for experimentation and I can't wait for the sun. :)


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Hi

Just like for a PST collimated etalon set up if you set the telescope focal point at the same point a F10 has its focus a parallel beam will be produced.

If the telescope is longer Fno it uses less of the etalon aperture and if shorter vignettes the objective.

You are better of experimenting with a PST etalon rather risking ruining the Lunt pressure tuned one, and voiding any warranty, it seems to me.
Once you can get the sealant locked screw threads undone.

Rusted, RodAstro has lots of experience using an 80mm objective to focal reduce his 6" F15 so that a DS60 quark module after it gives the required image size.

Cheers. Andrew.


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Carbon60 wrote: Thu Feb 02, 2023 7:28 am Interesting. I’ve also noticed that the alignment of the BF is important. If the BF is not mounted perpendicular to the axis of the light cone, then it can result in banding across the disk. Sloppy connections, or droop between the etalons and BF, can lead to this effect.

Stu.
Hi

Perhaps you need to simulate an optical bench, 3" alloy angle bolted onto the dovetail sticking out the back to support the etalon and imaging bits?

In his PST mods Peter Zetner used professional lens supports with adjusters on for the lenses and etalon. As I recall.

Cheers. Andrew.


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

marktownley wrote: Fri Feb 03, 2023 6:48 am Mounting any (ultra) narrowband image in a telecentric beam will have the effect of it having a tighter bandpass and reducing parasitic continuum leakag. This isn't necessarily from the off band comb peaks from the etalon but from scatter.

I do the same with my hi-res cak setup.
Hi

So will using my Combo after appropriate tele-extenders instead of the 4.2x, mean I will get a better image from the 21mm blocker/trim filter in the Combo as its in a tele-centric beam?

Where as the smaller 9mm blocker before the 4.2x is at a disadvantage here?

Cheers. Andrew.


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Re: Effect of blocking filter position on bandwidth.

Post by MalVeauX »

Hi,

I run my blocking filter in between my two air spaced etalons in this configuration:

collimation lens -> etalon 1 -> collimation lens -> Blocking Filter -> TZ4 Telecentric -> etalon 2 -> Eyepiece/camera

In a double stack, you can run the BF anywhere after the first etalon. The diameter matters based on the light cone where it sits to avoid vignetting and its proximity to things like focal reducers matter.

+++++++++++++++++++++++++++++++++++

As for using blocking filters to trim bandwidth, yes, they can do it. The closer to 1A bandpass the blocking filter is, the better. Every time you add another blocking filter that narrow, you are trimming the wings where the photosphere light leaks through. I have done this with normal 5~6A and 1.7A blocking filters and even two 1.7A blocking filters and could almost get rid of the double limb with just 1 etalon. Ultimately though 1A blocking filters cost more than an etalon does though.

Here's one etalon and two 1.7A blocking filters stacked for example:

viewtopic.php?p=284673#p284673

Very best,


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Re: Effect of blocking filter position on bandwidth.

Post by pupak »

If you have a BF of sufficient aperture, try putting it behind the TZ4 or behind etalon2 and you might be as pleasantly surprised as I was.


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Re: Effect of blocking filter position on bandwidth.

Post by MalVeauX »

pupak wrote: Fri Feb 03, 2023 2:18 pm If you have a BF of sufficient aperture, try putting it behind the TZ4 or behind etalon2 and you might be as pleasantly surprised as I was.
In general you will get better performance with long focal-ratio (or just think of it more as near parallel light rays) through any filter.

With 2 etalons this hardly matters (the placement of the blocking filter for this purpose), unless your etalons are very wide bandpass to begin with. It does matter with a single etalon and more narrow blocking filters.

Very best,


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Re: Effect of blocking filter position on bandwidth.

Post by Carbon60 »

AndiesHandyHandies wrote: Fri Feb 03, 2023 12:34 pm
Carbon60 wrote: Thu Feb 02, 2023 7:28 am Interesting. I’ve also noticed that the alignment of the BF is important. If the BF is not mounted perpendicular to the axis of the light cone, then it can result in banding across the disk. Sloppy connections, or droop between the etalons and BF, can lead to this effect.

Stu.
Hi

Perhaps you need to simulate an optical bench, 3" alloy angle bolted onto the dovetail sticking out the back to support the etalon and imaging bits?

In his PST mods Peter Zetner used professional lens supports with adjusters on for the lenses and etalon. As I recall.

Cheers. Andrew.
Thanks, Andrew.
The bolted angle alloy is the method I use on my 150 mm scope.

Stu.


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Ho Ho


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Re: Effect of blocking filter position on bandwidth.

Post by AndiesHandyHandies »

Rusted wrote: Fri Feb 03, 2023 6:31 am Thank you for your patience in expanding on your aims and to Andrew for teasing out more detail.

The F7 Lunt 60 etalon is pressure tuned so unable to perform "naked."
The collimation lenses are sealing the system. So their removal would destroy the ability to tune in the H-a band.

Those of us who invested in quality f/10 optics, for their PST mods, now find themselves at a disadvantage with Lunt's PT f7 modular etalons.
A weak positive lens added before the Lunt PT etalon would solve the problem.
Nobody has suggested a suitable lens so far. My own presumption is a quality, long focus achromat.
Of a minimum 40mm aperture to avoid vignetting. To convert f/10 to f/7 within the converging beam.

I haven't discovered a formula for calculating the required power of this lens at a suitable position.
An achromat may not even be necessary for monochromatic H-a use but opens up the possibility of using a small refractor objective.
Such lenses are intended for parallel light. So may be slightly "unhappy" working within a converging beam.

My apologies if I am drifting too far off the original topic.
Hi

There is no problem using the F10 telescope with the Lunt PT F7 etalon.
As long as the focal point is in the same place as for the Lunt used at F7.
All that is happening is that you are using a smaller part of the etalon with a slightly brighter beam.
Also the image might be a bit more contrasty as the cone is smaller and further from the sides.
Intensity does not matter. And glass, hard coatings and aluminium have high melting points.

'Leave that TZ alone'

Cheers. Andrew.


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