Solar hydrogen alpha line observation on the cheap?

[Newtownian]

For anyone with thoughts or experience?

I've long liked the idea of a Coronado but I simply cant justify the expense. So what I was wondering was about a cheaper conceptual alternative.

I have both a glass filter and Baader films for looking at the sun. They work as expected. They are good but the sun still doesn't show much definition beyond sunspots. And as anyone will know you don't see the remarkable images you get with narrowband hydrogen alpha images.

Now the glass filter is coloured yellow but the film filter is white suggesting it is letting through all wavelengths.

The obvious question this raises is can one simply put a hydrogen alpha filter into an eyepiece and get something approaching the Coronado images?? while of course using the Baader film as an upfront filter to maintain safety.

Now I know that you will get a big reduction in light - but with my 8" Cassegrain I would think there is more than enough light I think to compensate for say a 2 nm band pass filter (I might need a shroud and dark sensitivity adjustment time but that's ok). Alternatively maybe a deep red glass filter might give a lot of improvement.

With this in mind I looked around a little. Interestingly most glass filters don't come with absorption characteristics plots and most of the common filters aren't in the right range. The exception did seem to be Baader but they don't have a deep red glass filter.

But they do seem to have a number of hydrogen alpha filters with varying band pass width for CCD cameras at least http://www.baader-planetarium.de/sektion/s43d/s43d.htm

The main ones seem to offer 7nm and 35 nm bands.

Any comments on this idea?? The filters cost a bit but are still a lot cheaper than a full blown coranado.

[OICURMT]

First, I assume you meanusing the eyepiece filter IN CONJUCTION with the Baader film... if not, well, I'm certain you'll get a lecture or two in short order.

As for your idea... You'll never get the narrow band required to see any detail. The reason etalons are pricey is that they allow tuning within a very narrow band (generally less than 1 angstrom).

Baader filters would be in the 350 angstrom range. Much to broad for any detail (if you are comparing it to a Coronado).

OIC!

[N1 (Mirko)]

It's a fascinating subject and a great idea in principle, but as OIC points out, the band of nighttime filters is WAY too broad to show any detail. In fact, the band required is so narrow that the radial speed of prominences/filaments can sometimes render them invisible in a proper h alpha filter due to doppler shift. Tuning the filter to get them back into view is part of the fun observing the most dynamic object accessible to earth bound telescopes. Also the amount of appropriate-wavelength light that the eyesight-preserving and therefore essential white light filter in your setup passes through is ridiculously small, so even if you had a very narrow band filter at the other end, there wouldn't be much left to work with.

In short - if it worked, almost everybody would be doing it. The spectacular views of the star would ensure that.

There is an exciting alternative avenue, which may one day be one of my ATM DIY projects: A spectrohelioscope.

http://spectrohelioscope.org/page2.htm

http://www.cornellcollege.edu/physic...elioscope.html

I have never looked through one, but they seem to be marvellous devices. Look at the sketch of the solar disk in the first link. I have no idea why the likes of GSO aren't already churning these out. I reckon narrow band solar observing -and NOT limited to h alpha - would be accessible to even a modest budget. Going by the components used by the DIYers, they could be priced at well below $500. It may be one of the next great developments in the world of astro instruments.

Edit: Consider this related subject:

http://spaceweathergallery.com/indiv...pload_id=96189

This is so unbelievably good that I will not comment any further.

[Merlin66 (Ken)]

As mentioned DSO type Ha filters are unsafe to use for solar observing ( unless they are used a secondary filter behind a safe solar filter )

To effectively view detail in Ha the bandwidth needs to be around 0.1nm!!
hence the high price of specialised solar filters.

Spectroheliographs (SHG) are certainly a way forward (basically using a spectroscope with the telescope to acquire a video of the solar spectrum as the telescope scans the surface of the sun.)
Post processing of the video allows for the extraction of an image at any selected wavelength. The SHG and associated software is gaining maturity and I'd say within the next ten years will be a very workable solution.

[GUS.K (Ivan)]

When I first started looking into solar observing, I also thought the price of the products was expensive and that I couldn't justify the purchase,but took the gamble and bought a Coronado PST,and was hooked from day one.So hooked that three years down the line, three H alpha scopes, three H alpha filters plus a Lunt Solar wedge,I am still impressed with the views which can change minute by minute and I can say that it is now my primary astro activity(I have been a night observer for a couple of decades).
If you want great H alpha solar views the only real options are the dedicated H alpha scopes and filters.They might be expensive, but the effort that goes into making these scopes and the spectacular views they provide,even in the base models, is more than justified.

GUS.K

[N1 (Mirko)]

GUS, I couldn't agree more. After I got a SM60, I also had to have a small version (in my case the LS35), which has become my faithful travel companion. Relative to its size and cost, and coupled with a 20mm Plossl, it provides unparalleled enjoyment. Some interest in the Sun does help though

[GUS.K (Ivan)]

Hi Mirko ,I origianaly purchased the PST when the price came down to around $500.I was never really interested in solar observing(having only previously used eyepiece projection and full aperture filters on small refractors)but had seen a couple of photos through Ha scopes,and thought for the price I would give it a go,and it is now my main astro passion. I have numerous scopes from an18 inch Dob to a 100mm binocular telescopes,but the most used out of all my scopes is the Lunt 60 H alpha scope.

GUS.K

[Newtownian]

Tks for all this. I think I now understand the problem to a point. I was confusing nm and angstroms in my mind and didn't appreciate how narrow a band pass filter would be needed.

(Yes I was intending to use the Baader film too with any filter - so don't worry on that count)

I checked out Baader and other sites and cant see any 0.1 nm Bandpass at 656 nm.

Maybe its light reduction which with a Baader film is still a problem - at least 3000 (0.1/700-400nm) and in addition our eyes are not very sensitive this deep into the red part of the spectrum. So the fact our eyes vary greatly in sensitivity may not be enough.

Baader seems to offer some options but I have nil German and so cant tell whether they are claiming their H alpha filters work passably after-all or saying something else.

One thing about the small Coronado PST. It is pretty small and so doesn't perhaps give great resolution/magnification.

A final query about Coronado. Are there links to a description of their optics - diagrammatic or text? I couldn't find anything.

[Newtownian]

ps here is the link to the Baader stuff. http://www.baader-planetarium.de/sektion/s37a/s37a.htm. No I don't have any commercial interest. Its just they seem to be the only manufacturers who are serious about explaining the specifications of their products.

[Merlin66 (Ken)]

Mirko,
There are only two basic variations in Solar Ha telescopes.

The majority (PST/ 60 SolarmaxII/ Lunt 60/50 etc.) use a smaller etalon assembly behind the main objective. This saves money.
The optical layout is then:
Front objective (AR coated), energy rejection filter(ERF) (Lunt designs), collimating lens for narrow band etalon filter, re-imaging lens and energy rejection filter (Coronado). At the eyepiece/ camera end of all the Ha scopes there's a combination of IR rejection and final narrow band Ha filter (usually called the blocking filter)

The alternative construction uses an external ERF/etalon which fits onto the front of the scope i.e. Lunt 35/ Coronado SM60 etc.
The blocking filter assembly is still used at the eyepiece camera.
Hope this helps.

[OICURMT]

Originally Posted by Newtownian

I checked out Baader and other sites and cant see any 0.1 nm Bandpass at 656 nm.

You are missing the point. There does not exist any single filter that can give you the 0.1nm resolution required to view the specific Hydrogen Alpha wavelength.

The etalons previously described uses two plates that reflect the light back and forth within a narrow gap, which when tuned to a resonant frequency, allows light of a specific wavelength (with a narrow band) through. Any wavelength outside the tuned interval is "rejected".

Wikipedia have an excellent article on the subject -> http://en.wikipedia.org/wiki/Fabry%E...interferometer

Note that this relates to the etalon only. You will also need a blocking filter, which takes everything outside the Ha band and blocks it, allowing viewing of only the desired wavelength. Note that the blocking filter also screens out potential harmful wavelengths that still pass through the etalon (think harmonics).

OIC!

[GUS.K (Ivan)]

Hi Newtonian, there is a cutaway diagram of a Lunt solar scope showing all the filters and coatings necessary for safe solar H alpha viewing ,its on the Solarchat site in the commercial filters/Hardware section about 10 posts down.

GUS.K

[N1 (Mirko)]

Hi Merlin, yes I was aware of that. Both the SM60 and LS35 use front ERF/Etalon assemblies (before the objective lens) and BFs at the back. I unscrewed the Lunt when I first got it to see what's inside. Interestingly, the Lunt BF would not work with the Coronado Etalon and vice versa.

Cheers

Originally Posted by Merlin66

Mirko,
There are only two basic variations in Solar Ha telescopes.

The majority (PST/ 60 SolarmaxII/ Lunt 60/50 etc.) use a smaller etalon assembly behind the main objective. This saves money.
The optical layout is then:
Front objective (AR coated), energy rejection filter(ERF) (Lunt designs), collimating lens for narrow band etalon filter, re-imaging lens and energy rejection filter (Coronado). At the eyepiece/ camera end of all the Ha scopes there's a combination of IR rejection and final narrow band Ha filter (usually called the blocking filter)

The alternative construction uses an external ERF/etalon which fits onto the front of the scope i.e. Lunt 35/ Coronado SM60 etc.
The blocking filter assembly is still used at the eyepiece camera.
Hope this helps.

[pw (Peter)]

I'm surprised no-one has mentioned the Quark Ha eyepieces.
http://www.daystarfilters.com/Quark.shtml
Not cheap, but if you already have a small/medium refractor, then it seems like a good way to get into Ha solar oberservation at a lot less than the cost of a dedicated ha scope.

[N1 (Mirko)]

Peter, those are certainly interesting. I haven't quite got my head around the f/30 thing though - either stop down an already small aperture to be ridiculously small (affecting resolution and brightness), or barlow the telescope to make the FL ridiculously long (limiting observations to high power). Not sure how the former could be an improvement over the likes of the PST, or how the latter would be practical with the seeing the way it is on most days for many observers.

What are your thoughts on those limitations? Have you had the chance to look through one? What's it like?

Edit: With the Barlow built into the Solar Eyepiece, there is no need for anything extra - but the long-focal length issue remains. For 50x, you would already need a 30mm eyepiece on, say, an FS60 (355mm x 4.2 / 50). On many days, I find low power (20-25x) the best option for pleasing views and the 3-dimensional feel most apparent.

[Newtownian]

Originally Posted by OICURMT

You are missing the point. There does not exist any single filter that can give you the 0.1nm resolution required to view the specific Hydrogen Alpha wavelength.

The etalons previously described uses two plates that reflect the light back and forth within a narrow gap, which when tuned to a resonant frequency, allows light of a specific wavelength (with a narrow band) through. Any wavelength outside the tuned interval is "rejected".

Wikipedia have an excellent article on the subject -> http://en.wikipedia.org/wiki/Fabry%E...interferometer

Note that this relates to the etalon only. You will also need a blocking filter, which takes everything outside the Ha band and blocks it, allowing viewing of only the desired wavelength. Note that the blocking filter also screens out potential harmful wavelengths that still pass through the etalon (think harmonics).

OIC!

Tks - finally - you said the magic word that didn't jump out at me earlier - Etalon. Like most people I have had particular preconceptions about what a narrow band pass filter is - a circular piece of glass with high tech coating rather than this quite different refugee from an optical bench. To suggest the Etalon arrangement is a filter - which the sales blurb does - is like equating a Newtonian to a Cassegrain.

Still my dumb question seems to have stimulated a useful set of contributions from those who know better in what appears as a more specialist area of solar observing and helps he understand the passion here.

Why the manufacturers cant include such background in their own 'knowledge bases' beats me. Maybe the problem is their web sites are just set up to sell stuff using mainly hyperbole rather than getting people interested by explaining the fine details especially about the optics - which explain why these solar telescopes are even more remarkable achievements of mass production as their night-time counterparts... and good value for money if you can put a valid value on this in the first place.

[Newtownian]

Originally Posted by pw

I'm surprised no-one has mentioned the Quark Ha eyepieces.
http://www.daystarfilters.com/Quark.shtml
Not cheap, but if you already have a small/medium refractor, then it seems like a good way to get into Ha solar oberservation at a lot less than the cost of a dedicated ha scope.

This is a great site and illustrates for me how much more is out there and one of the problems with trying to find information via the internet using Google etc. ....... increasingly all you get is paid quickie buy and Teds camera store advertisements whatever search string you put in - which all prove to be useless - a bit like commercial television I guess.

[Joves (Aaron)]

I have the chromosphere Quark and can confirm that the view through it, whilst attached to my TV76, absolutely eats the view through my much loved PST alive!

They're an amazing new addition to solar observing.

[SteveInNZ]

Do you see anything of prominences with the chromosphere version ?
It sounds like having the choice of brakes or steering in a car.

Steve

[N1 (Mirko)]

Hi Aaron, sounds interesting. Where did you see the greatest improvements over the PST? Can you do full disk?

Originally Posted by Joves

I have the chromosphere Quark and can confirm that the view through it, whilst attached to my TV76, absolutely eats the view through my much loved PST alive!

They're an amazing new addition to solar observing.