Solar observing

Solanum · #1 16-10-2007, 11:07 PM

I don't see much on it here, but I'm interested. Can I buy, make (using purchased film) a solar filter for my 10" GSO Dob? I guess an off center reduced aperture type filter would be the significantly cheaper option.

What are my filter options? I think it would only be worthwhile if I could see some texture/sunspots on the disk and prominences.

Is the price going to make it not worthwhile on my dob? Are there major drawbacks in using my scope this way?

erick (Eric) · #2 16-10-2007, 11:19 PM

Probably your cheapest approach is here:-

http://www.iceinspace.com.au/index.p...63,136,0,0,1,0

Search for threads in the last 4-6 months - the topic has gone past a few times? The source of film is decribed in one of them.

I managed to get a relatively cheap second-hand Thousand Oaks off-axis small aperture filter for my 8", many thanks to an IISer and the IceTrade classifieds! It works quite well. Only tried it once and guess what, not a single sunspot to be seen - a pristine surface! I'm looking forward to some sunny days at Snake Valley to try some more.

Eric

erick (Eric) · #3 16-10-2007, 11:20 PM

Of course, I'm describing basic white light filters - really only for sunspot observing and possibly some surface granulation. For prominences etc., much bigger bucks are needed for H alpha filters!

Solanum · #4 17-10-2007, 06:20 AM

Thanks Erick, yeah it's the H-alpha and the like that I was thinking of rather than white light. I was figuring that the 10" would have enough umph to get a decent view with H-alpha. That's why I was wondering about options/cost and exactly what one would see. I did read that even with the PST scopes, which are H-alpha, the detail that can be seen is pretty limited.

iceman (Mike) · #5 17-10-2007, 06:25 AM

Hi Everard. You won't get Ha with a 10" scope. You just can't get a Ha filter that big, or if you could, you wouldn't be able to afford it.

For that aperture, you are limited to white light and as Eric pointed out, there's an article on how to build your own which is what I did. That will show you sun spots and minor surface granulation at higher mags and good seeing.

To see flares and prominenances, you need H-a, and your cheapest option is the PST at under $1000 (for 40mm aperture). You have to spend much much more than that to get larger apertures, and even then, it's still only 60mm aperture.

What you can see through a PST is actually quite good. It's just a matter of practise, and tuning in the filter to show the detail you want to see. I certainly wouldn't call it limited.

Solanum · #6 17-10-2007, 06:35 AM

Ah, thanks Mike, that was exactly the sort of answer I was after! Presumably an off center 40mm aperture filter would be cheaper than a PST, but no good in the 10" dob? (note that I have no idea of the maths involved with that type of set-up!).

Oh and Erick, I see the sunspot level is at an extended minimum of zero for some time now! http://sidc.oma.be/products/quieta/

[1ponders] (Paul) · #7 17-10-2007, 07:17 AM

Hi Solanum. IF you were able to get a 40mm off axis Ha aperture filter for your 10" dob, which in not very likely, you would not see anymore detail than you would with the PST. 40mm aperture is 40mm aperture whether it is a dob or a refractor (which is what the pst basically is).

To view Ha from the sun through a scope the front filter is only part of the system. In most filter situations you will also need a further blocking filter at the eyepiece end of the scope. Both filter structures need to be pretty well match/tuned to each other to do the job properly.

However if you search the internet you will find some references to converting an Orion ED80 to a solar Ha scope using the parts from a PST. I don't see how this would improve things because you will still be using the 40mm filter but there have been some positive reviews about doing this.

[1ponders] (Paul) · #8 17-10-2007, 07:29 AM

Here is one method here that doesn't use the original PST Etalon http://www.dd1us.de/Downloads/Modifi...0PST%200v3.pdf

Lots of images here http://www.astrosurf.com/re/sun.html and you might find more details here http://www.astrosurf.com/re/telescopes.html

Solanum · #9 17-10-2007, 08:16 AM

Ok! Ok!

Just to be clear, what I was thinking was that if one could mount a H-alpha (or similar - not sure what options there are, an He emission filter?) off axis one could get the equivalent of a PST (I wasn't expecting it to be better without a larger aperture), for significantly less due to not paying for the additional optics, eyepieces etc. Clearly, life isn't that simple! I certainly didn't realise further filters were required. But that's why I asked you guys.

For the record I wasn't intending to denigrate the PST, just that I've seen comments were people have been disappointed with the view - thus my wondering about a cheaper option. I suspect part of the reason for that disappointment is the PST advertising where they use superb pictures which were not taken through the PST (regularly on the back cover of A S & T for example). Whilst one doesn't expect to see quite that it certainly does build up the expectations.

[1ponders] (Paul) · #10 17-10-2007, 08:29 AM

You can check out some images taken through the PST here

http://www.iceinspace.com.au/forum/a...9&d=1179548846
http://www.iceinspace.com.au/forum/s...ad.php?t=16447