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Horatio

Solar Viewing and H-Alpha filter?

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Horatio    16

Hi there,  I've decided I'm going to make a solar filter for viewing the sun (baadar solar film) for my SW EVO80.  After watching Pete Lawrence on this months Sky at Night, he put a H-Alpha filter on too.   I'm a bit confused as there are so many different types of 1.25" H-Alpha filters at a vast range of prices.

I'm wondering what type would be most beneficial if I was to purchase one, as the price of some of them, makes me think if I was to pay that much then it's quarter of the way to getting second hand  Coronado PST and would possibly be better to save the money .

I will be attaching an Olympus OMD EM-5 to view...

So any advice is most welcome, thanks....

Edited by Horatio

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Your run of the mill 1.25" H-alpha filter is intended for deep sky work and has a bandpass of between 3 and 35 nm wide. A solar H-alpha filter is an entirely different beast, and has a bandwidth of 0.03 - 0.1 nm. These are far more expensive. One of the cheaper options is the Daystar Quark, which can be inserted into smaller refractors, turning them into H-alpha solar scopes. Deep sky H-alpha filters are not suitable for solar work and are positively dangerous if used without some VERY strong other filters to prevent dangerous light levels to reach the camera or (worse) your eyes.

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Stu    15,211
14 minutes ago, Horatio said:

Hi there,  I've decided I'm going to make a solar filter for viewing the sun (baadar solar film) for my SW EVO80.  After watching Pete Lawrence on this months Sky at Night, he put a H-Alpha filter on too.   I'm a bit confused as there are so many different types of 1.25" H-Alpha filters at a vast range of prices.

I'm wondering what type would be most beneficial if I was to purchase one, as the price of some of them, makes me think if I was to pay that much then it's quarter of the way to getting second hand  Coronado PST and would possibly be better to save the money .

I will be attaching an Olympus OMD EM-5 to view...

So any advice is most welcome, thanks....

Don't be confused into thinking that a standard H-Alpha filter used with Baader Solar film will show you prominences and other H-Alpha surface features such as filaments. You need a PST or similar dedicated Ha scope with the necessary very narrow bandpass in order to show these features.

I'm not sure why Pete was using such a filter, perhaps it helps to emphasise some of the white light aspects in a similar way to using a continuum filter.

I would save your money for a dedicated Ha scope.

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Horatio    16

Ah brill thanks Stu, I'm guessing that after a few goes with a baader solar film the sun spot novelty wears off. 

So thanks for the advice.... dedicated Ha scope it is (one day)

 

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MarsG76    1,703
8 hours ago, michael.h.f.wilkinson said:

Deep sky H-alpha filters are not suitable for solar work and are positively dangerous if used without some VERY strong other filters to prevent dangerous light levels to reach the camera or (worse) your eyes.

I second that... you wont recover your eyes once they're burned to sultanas..

 

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Stu    15,211
9 hours ago, Horatio said:

Ah brill thanks Stu, I'm guessing that after a few goes with a baader solar film the sun spot novelty wears off. 

So thanks for the advice.... dedicated Ha scope it is (one day)

 

Actually I still get plenty of pleasure from viewing in white light. The sun is not particularly active at the moment as it is near its minimum, but there are still active regions to see every now and then.

I use a Herschel Wedge with my scope, and find it gives better results than the film or glass filters. You can see finer detail and, in my experience, use higher powers so the detail around the active areas and in the granulation can be stunning at times when the seeing is good.

There is always more to see in Ha, but I will always have a soft spot for white light :) 

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ronin    3,755

Make yourself the white light solar filter, they are good fun to have. I sandwiched the film between 2 pieces of clear acrylic sheet from a hobby shop just for a bit of protection. You could also add to the eyepiece end an IR/UV cut filter, just for additional protection in case it concerned you.

After a "simple" solar filter come the Herschell wedge, they are good and even better if you add a continiium filter, comes out green and that will show sunspots well.

For the detailed stuff you need a dedicated solar scope, and they are not cheap.

The one that Pete Lawrence used was a bit of a surprise to me. I had no idea you could buy one that was used like a white light filter over the front of the scope and get Ha. I hadn't seen the program until a friend mentioned it so saw it on the repeat I made the effort to watch. Sometimes S@N is annoying, they mention things as if you can go pick up any scope and do the same. If that filter he used was as it seemed and did as implied (not really 100% sure) then I bet it cost several hundred £'s, or more.

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Stu    15,211
30 minutes ago, ronin said:

Make yourself the white light solar filter, they are good fun to have. I sandwiched the film between 2 pieces of clear acrylic sheet from a hobby shop just for a bit of protection. You could also add to the eyepiece end an IR/UV cut filter, just for additional protection in case it concerned you.

@Horatio, please do not follow this advice. Acrylic sheet is optically poor and putting two sheets (or four surfaces) in the way of your view will reduce the quality of the views. Baader solar film is designed to be used without other protection and is actually quite tough. If making your own filter, follow the instructions very carefully. The foils should not be tensioned in any way as this spoils its optical properties, a loose fit is best. Inspect it before every use and make sure that it cannot fall off or blow off during use.

EDIT Make sure you get the visual film which has higher blocking properties than the imaging version.

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Merlin66    877

Hmmm.

I'm not sure of the context of the Peter Lawrence situation.....

Sure, an Ha etalon objective filter will show Ha features....with a white light set-up (Baader film/ Herschel wedge) a secondary filter - Continuum, Ha DSO etc can subtly improve the visual contrast.........

 

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Stu    15,211
45 minutes ago, ronin said:

The one that Pete Lawrence used was a bit of a surprise to me. I had no idea you could buy one that was used like a white light filter over the front of the scope and get Ha. I hadn't seen the program until a friend mentioned it so saw it on the repeat I made the effort to watch. Sometimes S@N is annoying, they mention things as if you can go pick up any scope and do the same. If that filter he used was as it seemed and did as implied (not really 100% sure) then I bet it cost several hundred £'s, or more.

I've just viewed the S&N section with Pete Lawrence and it is clear that he is using a front mounted Ha etalon objective filter as suggested by Ken. Solarscope on the Isle of Man make these; very expensive but very good (having looked through Helen's 70mm)

http://solarscope.co.uk/sf-range.html

These are used in conjunction with a blocking filter at the rear to provide the necessary light reduction.

Not to be confused with a deep sky Ha filter used in conjunction with Baader film which will only show white light features.

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Horatio    16

Hey guys

Thanks for the replies, interesting stuff and loads to take in, I could really do with actually having a ganders through the different aspects of viewing ideally, solar film, Herschel wedge and solar scope, seeing as I've not actually looked through any....yet!

Solarsphere 2018 then it is for me! http://www.solarsphere.events/

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25585    193

I would like to do solar, but would want ground up specialist optics, and start with projected images or lookng at a monitor screen.

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Stu    15,211
On 01/12/2017 at 14:16, 25585 said:

but would want ground up specialist optics

That is not necessary, or even possible in the case of white light observing as far as I'm aware. A full aperture front filter on a standard scope, or a Herschel Wedge in the back of a refractor are the two main methods. Herschel Wedge is probably safer and gives better results. Just need to follow a careful setup routine.

There are numerous ways to skin the Ha cat, Lunt or Coronado make dedicated 'ready built' scopes, but the option of a front etalon and rear blocking filter fitted to a standard refractor is equally valid and can give excellent results, as can a Quark or PST mod.....

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Moonshane    10,306

Yeah what Stu said. Solar is perfectly safe as long as you use correct equipment responsibly.

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25585    193

Would not aiming a refractor at the sun without OG protection damage all the optics and the tube's internal structure from intense heat?

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Stu    15,211
12 minutes ago, 25585 said:

Would not aiming a refractor at the sun without OG protection damage all the optics and the tube's internal structure from intense heat?

No

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Stu    15,211
13 minutes ago, 25585 said:

Would not aiming a refractor at the sun without OG protection damage all the optics and the tube's internal structure from intense heat?

My apologies, my previous answer was a little brief. There are some things to be careful of. You should avoid scopes with oil spaced or cemented objectives and also those with any plastic parts internally.

Otherwise I stand by my earlier answer. I've used quite a few different scopes with Herschel wedges and also a Quark and have never had a problem, same for many others out there. We would not recommend doing the same otherwise.

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Moonshane    10,306

Just think of it like a magnifying glass with sunlight shining through on a piece of paper or your hand. It only gets hot at the point of focus i.e. when the image is concentrated I.e. at the eyepiece end. The wedge diverts all but 5% of the light and the filters remove all but 0.1% of that 5%

It's probably no brighter than looking down at a tarmac drive on a sunny day.

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25585    193

But how many people know if their scopes have plastic or cemented parts? Hardly any with sealed tubes I imagine, and even then...

 

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Moonshane    10,306

Best bet is ask whether a scope you are thinking if using for a wedge is suitable - either on here or via the retailer. Any scope (literally) would be ok with a well made and intact white light front end filter.

If you doubt that statement see the pic below 😁

1070_SolarObs_full.thumb.jpg.51df8357230c48bc24a0df481ff21fa4.jpg

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25585    193

Do the Lunt solar scopes have any particular construction aspects that normal scopes generally would not have?

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Moonshane    10,306

Not really. They are basically a cheap achromat refractor with specialist filtration. They are a singlet in some cases not even a double as it's not necessary to have expensive glass in monochrome Ha.

https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.stephenramsden.com/solarastrophotography/reviews/LUNT%20LS100THa%20review.pdf&ved=0ahUKEwj9ufO_hfnXAhXQaVAKHbBKCaQQFggcMAA&usg=AOvVaw20yk6N4C0FvsOh-1mIYgE9

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John    18,080

Having been brought up to believe that you never view the sun through an optical instrument, at first I was a little sceptical about using anything other than full aperture front end solar filters. Having owned and used a Lunt 1.25" Herschel Wedge for a couple of years now I'm much more comfortable about putting my eye to the eyepiece. I use the wedge with my 100mm, 102mm and 120mm refractors including at outreach events and it works very well.

I've very recently acquired a Lunt LS50 H-alpha scope (single stacked) and I'm intending to do more Ha observing next year with this. The initial couple of sessions that I've had with it have been pretty impressive but I'll need to wait and see how deep my interest is in Ha observing before I invest in double stacking it. The prospect of sitting in the sun feeling warm while doing astronomy is getting more appealing as I get older !

 

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Pete Presland    7,786

I would also "echo" John's comments, about "never view the sun through an optical instrument, at first I was a little sceptical about using anything other than full aperture front end solar filters". Now I also use a Lunt Solar wedge, with my 120mm refractor. It doesn't even get particularly warm, even after quite a long session.

As long as you ensure, the end cap stays on the end of the scope until the wedge is fitted you should have no problems. I also have deliberately removed the original diagonal from the tube and never refit it, to ensure I don't mix them up. Even though they are completely different colours and design. I did put the small plastic cap in the eyepiece tube once before putting the cap on the end of the tube, it had started to smoke within seconds!

Work cautiously and methodically and you will be fine. 

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