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sun filters?

lostinspace

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Merlin66

Merlin66

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John,

The available white light solar filters ( Baader/ 1000 oaks etc ) only allow you to safely view the surface of the sun. You will see sunspots and the surface granulation.

To see the sun with prominences etc you need to use a very expensive Ha filter or a Coronado PST telescope.

Ken

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lostinspace

lostinspace

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John,

The available white light solar filters ( Baader/ 1000 oaks etc ) only allow you to safely view the surface of the sun. You will see sunspots and the surface granulation.

To see the sun with prominences etc you need to use a very expensive Ha filter or a Coronado PST telescope.

Ken

thanks ken, i`ll look into them,

john

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Capricorn

Capricorn

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Just in case: Get a solar filter that fits over the aperture of the scope NOT one that goes in the eyepiece.

On the "inexpensive" side there are what I shall say are 2 varieties.

One is made from Baader film, a foil like material that is sandwiched between 2 sheets of glass. These are around the £30-40 mark depending on the diameter.

Then there is one that is made by depositing the material on the glass direct and this is then sandwiched (protection). Think these come out at £60-80.

Also don't forget that you cannot locate and centre the sun via a finder before viewing.;):eek:;) through the scope. Sounds unnecessary to say but when locating an object in a scope habit can take over.

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Mark at Beaufort

Mark at Beaufort

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John

I have an AC663 Sol-Vu full aperature solar observing filter to fit tubes 150mm to 179mm. You are welcome to try it out especially as we both live in the same town. I was not thinking of selling it but you are welcome to try it.

Send me a message if you are interested and we can meet up.

Same as this -

http://www.pulsar-optical.co.uk/prod/solar-observing-filters/telescopes/binoculars/sun-filter

Mark

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brianb

brianb

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On the "inexpensive" side there are what I shall say are 2 varieties.

Baader solar film (and the commerical units made using it) are way superior to glass ones in optical performace (unless the glass filter is VERY expensive; the Zeiss units are good but have a four figure price tag!) and probably tougher as well. They resist careless finger pokes and don't shatter if accidentally dropped. The only downside is that you can't clean them effectively.

All solar viewing equipment needs to be carefully checked for cracks / splits / light leaks etc. on EVERY occasion it is used ... if not treated with respect, observing the Sun can be very dangerous indeed.

It goes without saying that cheap glass filters which are used at the eyepiece end of the scope are useless for protection. They will shatter or even melt with the concentrated solar heat. Using extra filters in the eyepiece in conjunction with a proper objective end solar filter can be helpful, especially with a short focus refractor, a green filter (#58) is cheap and very effective though the expensive Baader Solar Continuum filter is maybe a bit better at enhancing the detail.

don't forget that you cannot locate and centre the sun via a finder before viewing

Indeed. Either make a seperate Baader film filter for the finder, replace it with one of the dedicated solar finders which work on the pinhole principle (Televue Solsearcher, Coronado Solranger) or remove it altogether & find the sun by the principle of minimizing the area of the OTA shadow. The first few times you try the last method you will get infuriated but, if you stick at it, you will eventually acquire the knack.

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johninderby

johninderby

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The Baader film is the next best thing to a Herschel Wedge in terms of performance in white light solar observing, but is a fraction of the price. Herschel Wedges though only work with refractors as they replace the diagonal whereas the Baader film fit's over the front of a telescope and can be used on any type of telescope.

If you look at the commercial filters using the Baader film you'll see that the film looks loose and baggy. That's the way it's supposed to be as pulling it tight causes optical distortion. The Baader film is surprisingly tough and will withstand punishment that would shatter a glass filter.

I would think that a really good glass filter of say 6 inches that would match the performance of the Baader film would be getting towards £1,000.00.

John

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lostinspace

lostinspace

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thanks for all your advise guys, ive looked into it and found a shop in birmingham that does the film that you suggested. he told me to cut a piece out and place it over the end of the scope ( removing only the cap ). also he said each piece was good for only one session, and to be very carefull not to scratch or pierce it. apparently it comes in a4 size sheets at £18 each. youv`e all been very helpfull on this, thank you.

Mark.., thank you for your offer, that would be good. i will see you at the next astronomy meeting at the kindle centre?

john

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johninderby

johninderby

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The Baader film will last for years if looked after properly, and it shouldn't just be fastened over the end of the scope. You should make up a very simple cell to hold it.

Here's Baader's instructions for a home made cell using bits you should already have laying around the house. A Blue Peter type of project.

http://www.baader-planetarium.com/sofifolie/bauanleitung_e.htm

John

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Capricorn

Capricorn

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Capricorn,

Just a correction....

The Baader Solar Film is actually a patented polymer film ( It's not mylar!) coated on both sides ... no glass.

Excellent, cost effective, safe performer if used correctly.

Ken. Post says it is a film, I do not mention Mylar. So why the correction.

The ones I have seen to buy have been part of a sandwich, stops small holes etc appearing in the film - safety and more robust.

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lostinspace

lostinspace

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I've never heard the "one session" thing before with Baader film.....

i think he was being extra cautious as he did say be very, very carefull not to damage or scratch the surface of the film and to be thorough when checking. i guess he could of also wanted me to keep buying the film, but TBH i think with my inexperiance showing, he was just being safe, thanks again peeps,

john

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johninderby

johninderby

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The idea of sandwiching the Baader film between sheets of glass is a really, really bad idea. Obviously thought up by someone who is totally clueless.

First of all the film is pretty tough and doesn't need the protection and most importantly the glass will ruin the optical qualities of the film and introduce all sorts of distortion and reduce contrast.

While technically speaking it could be done if you used proper optically flat glass it would be so expensive it wouldn't be practical. Think in terms of such a filter with two pieces of such glass costing in the order of £2,000.00 for a 6" filter.

John

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michael.h.f.wilkinson

michael.h.f.wilkinson

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You'd be lucky to get one piece of optically flat glass in 6" aperture for that price!

Why is that? The Schmidt corrector plate in my SCT is 8" in diameter and sure as hell did not cost GBP 2000,00 (the entire scope did not cost that much), and that is not flat but a more complicated aspherical shape. Flat surfaces are way easier (not trivial of course) to shape. A slightly bigger problem might be depositing the metal evenly.

Note: the traditional way of grinding and polishing a Schmidt plate was by providing annular support, drawing a partial vacuum so the glass is distorted, and creating an optically flat surface. Once pressure was released the final surface was correctly warped.

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johninderby

johninderby

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A true opticly flat plate is actual WAY harder to make. An SCT correcter is comparatively easy to make once the tooling is sorted out and with an SCT the small secondary mirror can be touched up to correct for the errors in the corrector plate and then the primary can also be touched up as well. A cheap and easy fix.

To get a plate of glass that is truly flat on both surfaces and keeping both surfaces parallel is very technically challenging. You can't just touch up a part of the surface that say has a dip in it as this means re-doing the entire surface all over again. And then there are the added complications of getting the other surface right as well without distorting the first surface. And if you add coatings then they have to be equal and perfect on both sides as just doing one side would cause distortions. All in all a bit of a nightmare to manufacture.

Take a look a Baader's D-ERF filters for example. A 160mm D-ERF filter will set you back £800.00. And from what I hear Baader actually scraps most of the filters that they make as only a few are good enough. Another factor that makes them so expensive.

John

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brianb

brianb

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Why is that?

Volume, dear boy ...

The glass solar filters sold under the Thousand Oaks & Orion brands perform very badly, rather like looking through window glass, which is what I strongly suspect they're made of. The Zeiss glass filter works well but costs over £1000 in 4" size.

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michael.h.f.wilkinson

michael.h.f.wilkinson

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I will give the solar screen a shot (can borrow some from a colleague) and compare it to a glass filter I have lying around (not a Zeiss).

Incidentally, a slight prismatic error is tolerable on filters (I have seen and measured this in dichroic filter sets used in fluorescence microscopy (Leitz filters, no less)). It tends to just shift the image without showing much in the way of colour fringes. We used to take multiple shots at different wavelengths with a monochrome CCD, and had to shift the results back. Because the error was fixed, we could realign digitally very effectively.

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Merlin66

Merlin66

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SOHO MDI Continuum Latest Image

This is a current white light image of the sun....

You can see the small sunspot groups....

At about x100 you should be able to see the sunspots and the surrounding details.

Start by focusing on the edge of the sun's disk, when it's as sharp as possible look at the surface. It sometimes helps ( reduces vibration etc) just to let the disk of the sun drift across the field of view.

There's not a lot of activity at the moment, but that can quickly change...practise, practise, practise

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