Other Bands to View the Sun?

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Other Bands to View the Sun?

Post by Brett »

Lunt, Coronado, Daystar and many others are treating our eyes and cameras these days to the wonders of the Sun in H alpha and CaK bands.

I am wondering what other bands possibly may be in our future that may be interesting? Helium? H beta?

Would manufacturers consider bringing this to the eyepiece and if not, why not?


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Re: Other Bands to View the Sun?

Post by solarchat »

Daystar sells etalons in several different wavelengths now including H-beta, Helium and Sodium. I think no one else offers them probably because there is almost no market.


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Re: Other Bands to View the Sun?

Post by Brett »

Thank you for that info Stephen, I was not aware of that.

Are there any links to images using these filters?


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Re: Other Bands to View the Sun?

Post by marktownley »

Right here, today, on this very forum http://solarchat.natca.net/viewtopic.php?f=8&t=14283


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Re: Other Bands to View the Sun?

Post by pbsastro »

Mark from SolarSpectrum told me this week:
"I can make etalons from 390nm- 900nm with the setup I have.
I have made Na filters."

I am considering a Sodium (Na) filter, instead of a WL wedge.
For a Na ERF I am considering a Baader D-ERF tilted enough to shift bandpass to include Na line. Baader D-ERF range starts at about 610nm and Na is 590nm so I need a 20nm shift. From my calculations that requires a 20 to 30 deg tilt, which is severe but doable.
For this purpose I would like to test the ERF with a spectrometer with different angles to get the best angle. Can anyone recommend a spectrometer service within EU?

Pedro


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Re: Other Bands to View the Sun?

Post by Merlin66 »

Pedro,
I can probably assist.
I have access to a 0.1A resolution spectroscope and I also have a Baader D-ERF.
Give me a few days......


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Re: Other Bands to View the Sun?

Post by Valery »

pbsastro wrote:Mark from SolarSpectrum told me this week:
"I can make etalons from 390nm- 900nm with the setup I have.
I have made Na filters."

I am considering a Sodium (Na) filter, instead of a WL wedge.
For a Na ERF I am considering a Baader D-ERF tilted enough to shift bandpass to include Na line. Baader D-ERF range starts at about 610nm and Na is 590nm so I need a 20nm shift. From my calculations that requires a 20 to 30 deg tilt, which is severe but doable.
For this purpose I would like to test the ERF with a spectrometer with different angles to get the best angle. Can anyone recommend a spectrometer service within EU?

Pedro
You can go another way - use a DayStar yellow ERF.


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Re: Other Bands to View the Sun?

Post by swisswalter »

Hi Valery

have you the specs from that Daystar ERF down to 3900 A, may be that is also something for CaK jobs?


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Re: Other Bands to View the Sun?

Post by pbsastro »

Thanks a lot Merlin, that would be great.
My current 180 D-ERF is already mounted at 2 deg to avoid reflections between ERF and etalon.
We are lucky that tilting shifts wavelength to the blue, or else nothing could be done :-)

Valery, the yellow glass filter does not reject all the heat as the Baader ERF does, but yes it can be used. But if D-ERF can be shifted I will prefer it as ideal solution.


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Re: Other Bands to View the Sun?

Post by Valery »

swisswalter wrote:Hi Valery

have you the specs from that Daystar ERF down to 3900 A, may be that is also something for CaK jobs?
Hi Walter,

No, I don't have any specs from the DayStar, but I suspect, that it is not possible to work at 3900A with that filter.

Please, contact me via e-mail if you do need your own special filter. Right now we do work about such solar filters
of different diameters and specs.

My 150mm scope can work at CaK, H-a and at 430nm (Fe line) .


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Re: Other Bands to View the Sun?

Post by swisswalter »

Hi Valery


thank you very much


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Re: Other Bands to View the Sun?

Post by mdwmark »

A yellow will work for Na wavelength. Orange or light red would be better.
For K-line,
An yellow filter will just block any blue light. It is not for the blue. An ERF made from BG36 may be a good ERF choice. It will transmit both K-line and Ha and block a lot of the light in between.
If you want to be fancy. You could make a two bandpass filter. One at K-line (H-line) the other around Ha, or Na and Ha. The problem is the cost. Making small runs would cost a lot.
The reason there is not a lot of different wavelengths to look at is that most look the same.
I always found it ironic that the best wavelengths to observer are the ones where your eyes have a hard time seeing.That not counting the ones in the IR where you can only see with a camera.
Mark W.


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Re: Other Bands to View the Sun?

Post by swisswalter »

Hi Mark

thank you for the informations


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Re: Other Bands to View the Sun?

Post by marktownley »

Yes, thanks Mark.


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Re: Other Bands to View the Sun?

Post by Valery »

mdwmark wrote: The reason there is not a lot of different wavelengths to look at is that most look the same.
I always found it ironic that the best wavelengths to observer are the ones where your eyes have a hard time seeing.That not counting the ones in the IR where you can only see with a camera.
Mark W.
Thanks, Mark.

The Ca K or Ca H -> 430nm -> Ha all look very different with their own specific structures.

What other wave lengths will show the Sun significantly different even if they are in IR ?

Thanks,

Valery.


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Re: Other Bands to View the Sun?

Post by Merlin66 »

Pedro,
I don't have my spectroscope seriously set up right now (re-building the observatory)
But I was able to fit a Baader D-ERF to my 600 l/mm instrument .
Just visual at the moment to verify what was possible....
Set the spectrum to solar Ha, fitted the ERF an as expected the Ha was close to the central pass bandwidth.
I then set the spectroscope to the Na lines. With the ERF fitted they were no longer visible ( as expected!), and tilted the ERF to see if they would come into view.....
No way! Even with around a 30 degree tilt the pass band of the ERF was still well into the red.
I can quantify the results if you need specific figures, but IMHO tilting a D-ERF will not reach the Na region.....


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Re: Other Bands to View the Sun?

Post by swisswalter »

Hi Ken

an interesting outcome of that test. Thanks


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Re: Other Bands to View the Sun?

Post by marktownley »

Thanks ken


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Re: Other Bands to View the Sun?

Post by pbsastro »

Thanks a lot Ken for the test.
Unfortunately the results are disappointing.

From what I found the shift in wavelength is given by:
wf=wi x sqr(1-(sin(A)/n)^2)
where:
A is the angle
n is the refractive index
wf and wi the final and initial wavelengths

I am not sure of the refractive index of the ERF, but I assumed it is between 1.5 (BK7) and 2.
From Baader transmission graphic, we see it starts at 610 nm. Na is about 590 nm.

So, for wi=610, A=30 and n=1.5 we get wf= 576 nm
and for wi=610, A=30 and n=2 we get wf= 590 nm

So, if the transmission graphic is correct, the refractive index should be higher than 2,
or I have my calculations wrong...

But thanks again for your testing Ken.
If you have the opportunity in the future, it would be interesting to know how far we are from the required 590 nm.
The no tilt transmission is steep at 610, but I guess shifted it should be less steep, so it would give some signs if it were really close.

I guess orange or yellow glass may be in my future as suggested by Mark.

Thanks,
Pedro


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Re: Other Bands to View the Sun?

Post by Merlin66 »

Pedro,
OK I'll give it another go....
The "tilt" mechanism needs to be a bit more sophisticated than "visual by eye"
I'll rig up the spectroscope on the bench and use the in-built neon for calibration.
It's just dawned on me while typing this.....the ERF I tested may not be identical to the D-ERF.
(I've been using a Baader CCD Ha 35nm filter as an ERF and that's, I'm sure, the one I tested!!)
I have the D-ERF...give me a day or so......


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Re: Other Bands to View the Sun?

Post by Valery »

Merlin66 wrote:Pedro,
OK I'll give it another go....
The "tilt" mechanism needs to be a bit more sophisticated than "visual by eye"
I'll rig up the spectroscope on the bench and use the in-built neon for calibration.
It's just dawned on me while typing this.....the ERF I tested may not be identical to the D-ERF.
(I've been using a Baader CCD Ha 35nm filter as an ERF and that's, I'm sure, the one I tested!!)
I have the D-ERF...give me a day or so......

All your efforts are worthless because of simple mistake = Baader D-ERF filter is absorption filter.
It irrelevant to the tilt.

It has interference filter for IR blocking. Only there you can obtain bandpass shift due to tilting.

The orange or yellow glass is a way to go.


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Re: Other Bands to View the Sun?

Post by pbsastro »

OK, Thanks Ken!

Valery, I think you are assuming the D-ERF is made of red glass. That is the C-ERF that is made of red glass and then uses dielectric to refllect IR. The D-ERF is made of clear glass, it uses dielectric to filter everything below 610 and above 680.

In fact I just checked my D-ERF holding it by hand and looking at the sun through it. At 30 deg I can see red, yellow and a shade of green. From 60 to 90 deg it is completely green.
Then I pointed the ERF at an apparent pure yellow object. No tilt object is red, 45 deg tilt it is pure yellow (original color), 60-90 deg is pure green.

Sodium is yellow, so it is definitively below 60 degrees tilt, maybe between 30-45.
In fact this seems to match my calculations as it gets to pure green, but no blue.

So I had the way to proof-test it my hands all the time and did not remember to do it.
But the spectrum analysis is still important to check where the Na line(s) lye in the transmission curve.

In fact I think the D-ERF could be just the perfect ERF for Na. Besides rejecting UV and IR, looking at the D-ERF curve, it transmits near top top transmission from about 610 to 680. If we shift that 23nm to the blue we would get 587 to 657, which is just right to include at the same time Ha, Na and HeD3!
It may seem a bit tight (no margin), but the shifting comes with broadening as well, so if the transmission curve is correct I think that there will be some margin, and with exact tilting, the ERF can include all those three (Ha, Na and HeD3). The transmission will be a little below maximum, due to broadening and due to be near the bandpass limits, but that is what the spectrum analysis will tell us, and the ideal tilt angle. To include the three lines there is no much margin, the angle will have to be rigorous.

If I just had a source of pure Na (590nm) light, I could do a more accurate test myself without spectrometer. I already have a source of pure Ha with a "night sky" Ha filter, I would need the equivalent for Na light. But the full spectrum graph will be much better as it shows clearly all that is happening.

Pedro
Last edited by pbsastro on Wed Jan 21, 2015 3:46 pm, edited 4 times in total.


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Re: Other Bands to View the Sun?

Post by pbsastro »

Now I would welcome opinions about what is best for visual. Na or HeD3. I will go only with one of those. Na and HeD3 are so close, only 2nm (20A) apart (587.5 and 589.5) that we could think it could be possible that just one filter could reach both with extra tuning, but I think the blockers would need to be different.
From the sample I see Na and He are similar, mixing WL view with plages and faculae. My thing is that I love CaK views, but I am reducing it to near zero, due to possible eye damage, so I am considering that Na could give me the same faculae and plages in a WL background. It may may not look so good as in CaK, but the Na light is much more visible to the eye, so that could be an advantage for visual. And it would give two in one (WL and CaK). But I guess if it were good enough it would be more used.
Looking at some graphics, the HeD3 line seems to be too weak relative to close neighbor lines, so I fear it may require some image processing and be not so adequate for visual.

Another issue is that both Na and He lines are narrow, below 0.4A, so that Mark suggests double stack may work better, so it will not be no easy to get equivalent samples to help decision.

Pedro
Last edited by pbsastro on Wed Jan 21, 2015 12:23 pm, edited 1 time in total.


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Re: Other Bands to View the Sun?

Post by marktownley »

My only concern with tilting an ERF by so much would be that it is introducing astigmatism...


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Re: Other Bands to View the Sun?

Post by pbsastro »

On the other hand color glass has significant less quality than clear glass, so I think the tlilted clear glass will still be better than the non-tilted color glass.

One issue with the clear glass is that it does not block completely the yellow-green light, less than 1% remains (one can check it in the transmission graph). That is no problem with filters that have red glass included as the SolarSpectrum filters or the Lunt internal modules. But when using the D-ERF with my rear-mounted air-spaced I need to use a Baader 35nm Ha filter to get rid of the residual yellow-green. When using the C-ERF no need for the 35nm filter.

Another issue is that such severe tilting, will reduce the ERF effective aperture about 20%.


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Re: Other Bands to View the Sun?

Post by Valery »

pbsastro wrote:Now I would welcome opinions about what is best for visual. Na or HeD3. I will go only with one of those. Na and HeD3 are so close, only 2nm (20A) apart (587.5 and 589.5) that we could think it could be possible that just one filter could reach both with extra tuning, but I think the blockers would need to be different.
From the sample I see Na and He are similar, mixing WL view with plages and faculae. My thing is that I love CaK views, but I am reducing it to near zero, due to possible eye damage, so I am considering that Na could give me the same faculae and plages in a WL background. It may may not look so good as in CaK, but the Na light is much more visible to the eye, so that could be an advantage for visual. And it would give two in one (WL and CaK). But I guess if it were good enough it would be more used.
Looking at some graphics, the HeD3 line seems to be too weak relative to close neighbor lines, so I fear it may require some image processing and be not so adequate for visual.

Another issue is that both Na and He lines are narrow, below 0.4A, so that Mark suggests double stack may work better, so it will not be no easy to get equivalent samples to help decision.

Pedro

If I will be you, I'd never spend money for any of these yellow filters. Too insignificant difference vs, for example, green light.
May be G line at near 430nm? At least much higher granulation contrast.

I may be well wrong in my reasoning, but I really never saw any impressive image of the sun through these yellow filters.


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Re: Other Bands to View the Sun?

Post by Valery »

Here one can see sun photos (not that of high quality) He and Sidium Na .

He D3 looks more interesting.

http://www.company7.com/daystar/products.html


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Re: Other Bands to View the Sun?

Post by Merlin66 »

OK under better control conditions ( and using the proper Baader D-ERF - Doh!)
I've obtained some calibrated spectra in the region around the Na lines with 20/25/and 30 degree tilt. I've also check the bandpass at Ha with the 30 deg tilt.
This definitely shows the D-ERF can be set to a 30 degree tilt (and probably slightly more) and pass both the Na and Ha lines.
Any questions let me know.
DERF tilt Na.JPG
DERF tilt Na.JPG (111.23 KiB) Viewed 3501 times
DERF tilt Ha.JPG
DERF tilt Ha.JPG (112.45 KiB) Viewed 3505 times
Last edited by Merlin66 on Fri Jan 23, 2015 3:28 am, edited 1 time in total.
Reason: rescaled Na profile


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Re: Other Bands to View the Sun?

Post by Valery »

The only question remains: is it worth of money and efforts and what special to look at? I mean in Na or He D3 lines.


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Re: Other Bands to View the Sun?

Post by swisswalter »

Hi Ken

great presentation of the interesting results


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Re: Other Bands to View the Sun?

Post by marktownley »

Good graphs Ken, good question Valery!


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Re: Other Bands to View the Sun?

Post by pbsastro »

Thanks a lot Ken. Great results, not only the shift lets Na and He in but also keeps Ha at near full transmission.
It also proves the minimum tilt is 30 degrees, a little more if we want full Na/He transmission.

Meanwhile I tried my D-ERF (hold by hand) against some street lights, which I think are mostly sodium emitting, and the results match this exactly:
0-20 deg: dark red
30 deg: yellow, medium brightness
45 deg: pure yellow, maximum brightness
60-90 deg: full green
So this quick test suggested 30 deg as minimum and 45 deg for ideal transmission, but it was not conclusive because I don't have the isolated Na line. The spectrometer is the proof and tell us the whole trend of the curve.

So, D-ERF tilt It is a very cheap way (no glass to buy, just a tilting adaptor) to get a multi-ERF, and a very god one, because being D-ERF, it fully blocks UV and IR.
Thanks a lot Ken!


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Re: Other Bands to View the Sun?

Post by pbsastro »

Valery wrote:The only question remains: is it worth of money and efforts and what special to look at? I mean in Na or He D3 lines.
Valery, is WL worth the money, effort and risks?
I am not sure but it it seems Na (or He) is at least as good as WL, with added benefits.
I don't like heat getting inside my scopes (accidents, heat waves, etc). So I decided not to waist money on a WL wedge, so I started saving there. Now I don't have to buy a new ERF, saving again.
Now I am wondering if it would not be possible to use the same etalon/oven/controller for Ha/Na/He, switching only the blocker. Is the blocker required to be inside the filter housing? MarkW can you help here?
Even a double stack could be shared by just switching the blocker?

The main problem I see with Na (or any other filter) is that the Euro lost 23% to the USD and narrowband filters (all USA made) are looking worse each day.

Now Valery, I am very interested on comparing images of Na and HeD3, but there seems to not be many around, specially high resolution.

Pedro


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Re: Other Bands to View the Sun?

Post by marktownley »

The biggest problem I see with tilting an ERF so much is the astigmatism it will introduce....


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Re: Other Bands to View the Sun?

Post by Valery »

pbsastro wrote:
Valery wrote:The only question remains: is it worth of money and efforts and what special to look at? I mean in Na or He D3 lines.
Valery, is WL worth the money, effort and risks?
I am not sure but it it seems Na (or He) is at least as good as WL, with added benefits.
I don't like heat getting inside my scopes (accidents, heat waves, etc). So I decided not to waist money on a WL wedge, so I started saving there. Now I don't have to buy a new ERF, saving again.
Now I am wondering if it would not be possible to use the same etalon/oven/controller for Ha/Na/He, switching only the blocker. Is the blocker required to be inside the filter housing? MarkW can you help here?
Even a double stack could be shared by just switching the blocker?

The main problem I see with Na (or any other filter) is that the Euro lost 23% to the USD and narrowband filters (all USA made) are looking worse each day.

Now Valery, I am very interested on comparing images of Na and HeD3, but there seems to not be many around, specially high resolution.

Pedro
Pedro,

You didn't take my point. Na or He D3 _narrow_ band etalons are NOT worth their price cause their minor new features are not enough to justify the
major additionsl cost. I'd better spend these money as follow (one of them):

1. Large aperture WL imaging - larger SCT + Baader Solar film or Baader Herschel prism
2. Double stack of H-a or buy significantly narrower filter or increase aperture as well
3. Double stack CaK with aperture rise

Any of these way to go will benefit more than a Na or He D3 etalon. These etalons are necessary for solar scientists, not for amateurs who just spend
the time and money on the hobby and are hunting for impressive pictures and not for extracting of the scientific data.

Valery.


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Re: Other Bands to View the Sun?

Post by Valery »

marktownley wrote:The biggest problem I see with tilting an ERF so much is the astigmatism it will introduce....
To escape of astigmatism, you need to place another flat transparent plate of the same thickness as the BF and tilted versa.

Like this ========== /== \ =====>| F'

Where / - Block filter \ - counter flat plate.

Valery.


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Re: Other Bands to View the Sun?

Post by marktownley »

This is the arrangement I have done with filters in my CaK stack Valery ;)

To be honest, if I was looking to observe / image down in 500nm region I would probably just use a UV/IR cut on the nosepiece of the telecentric at apertures less than 100mm. Above 100mm aperture the Baader UV/IR cut is available in larger sizes and would just mount a larger version sub aperture in the tube.


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