Solar Observing

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Solar Observing

Postby gas1883 » Sun Aug 21, 2011 2:36 pm

I was wondering if it would be possible to view the Sun with my Reflecting Telescope, I am also fully aware of the dangers of looking directly at the Sun.

My tube end cap has a smaller cap that can be removed leaving an approx. 2" hole in the main cap, is this for Solar viewing, I have read that observing the Sun with a Reflector can damage the mirror(s) and optics, so, is this to allow for less light to enter the tube so as not to damage the scope?
Do I need a Solar Filter, or is this to allow you to see certain aspects of the Sun?

I would be observing the Sun reflected onto a piece of white paper.

Has anyone heard of people using "Bristol Board" for observing the Sun?

Thanks in advance.
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RE: Solar Observing

Postby wilkibo » Sun Aug 21, 2011 6:30 pm

The smaller end cap (which is offset from the centre) is actually to spefically exclude the image of the secondary mirror + supports from the eyepiece output. [b]IT DOES [u][u]NOT[/u][/u] REDUCE THE POWER SUFFICIENTLY TO SAFELY VIEW AN UNFILTERED IMAGE[/b] ie you [b]still[/b] need to put a [b]white light filter[/b] over the [b]smaller opening[/b]
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RE: Solar Observing

Postby les » Sun Aug 21, 2011 7:36 pm

HI Rob,
You can us the off centre aperture for Solar projection or you can use Baader Solar Film to make your own filter to fit the aperture by making a cardboard tube.Great care should be taken making this,you must make sure its safely made with stiff enough cardboard and the filter tube fits the aperture snuggly and is deep enough within the cap that it cant get blown out while observing.Detailed instructions are given with the pack.A home made Baader filter must be remade and checked regularly for pinholes and changed at least every season.I ordered some Baader film earlier today and its £21.99 inc VAT and postage I was shocked at how much its gone up since I last bought some about 5 years go.That was from Telescope House,I couldent be bothered to shop around.
Regards and clear skies Les.
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RE: Solar Observing

Postby lancashire astroguy » Sun Aug 21, 2011 9:50 pm

Hi Rob,

If your scope is expensive I would be wary about using the projection method even with the small aperture in the end cap. All that light and IR radiation could cause a lot of heating inside your scope which isn't going to do the optics any good. Then again if its a cheap scope, its a perfectly safe and effective way to observe the Sun.

Using Baader filter paper is probably your best bet. I fully concur with what Les has said about checking for pinholes regularly (I check every time I observe through them in fact). An A4 sheet of the stuff is quite pricey, but I managed to make filters for my 130mm Skywatcher reflector (again, the 2 inch aperture in the end cap) and my school's 80mm refractor. There was enough left over at least for a pair of binoculars - I actually made 3 pairs of eclipse glasses. The paper is really fragile and flimsy and I found it a nightmare to cut. You have to be pretty proficient with card and superglue too. I'm a disaster at anything practical and this gave me several hours of frustration. The Baader paper was really hard to stretch flat without creasing when sandwiched between the card. I finally resorted to using a staple gun! Nonetheless it was worth it in the end - for me the view using the filter is far crisper than anything I can get with projection.

Regards,
James

P.S. For any newbies reading is, it is important to point out that you should only make a Baader filter to fit over the objective lens (or mirror) end of the scope and NEVER at the eyepiece end. If the filter was at the eyepiece end, the focussed sunlight could burn straight through it and into your eye. Nasty!
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RE: Solar Observing

Postby arthur dent » Wed Aug 24, 2011 2:50 pm

Here is a step-by-step fabrication of a solar filter for my RACI finder (the scope already had one and I had some spare solar film...)

Art finally got down to fabricating a solar filter for his RACI finder using Baader solar Film.

The procedure would be exactly the same for making a DIY filter for your telescope (except that the front baffle/lens hood/dew shield of the RACI can be unscrewed and, being smaller, is probably easier to manipulate the pieces during fabrication.

During this procedure - I'll be referring to the parts of the RACI - translate this into the appropriate parts of your telescope.

Cost? A couple of pounds for the film and a couple of pounds for the roll of silver Duck tape from B&Q. Cardboard courtesy of a M&S ready meal deal ("Dine in for two for £10") last week! So, say £6 in total (or US $10).

First, a picture of the RACI finder:

Image

Measure the outside diameter of the RACI (telescope) - the dew shield. You are going to make a carboard tube to be a snug fit around this part.

Here, the o/d of the RACIs dew shield is 18.5cm (7¼" for my US buddies):

Image

Using a piece of thin but flexible cardboard, draw out a net for a cylinder. I included 4 tabs (to stick the film-retaining cardboard rings to) but 8 or 12 would probably have been better with hindsight. Not wanting the filter to be blown off by the wind or knocked off accidentally, I went for a deep filter cap (35mm or 1 3/8"). Here is the drafting of the net:

Image

and the net cut out with the tabs and two cardboard circles (soon to be rings) to retain the solar film. I eventually ended up cutting out three cardboard rings. The o/d of these rings is just slightly smaller than the o/d of (what I'll call) the dew shield:

Image

The net for the tube is wrapped around the dew shield and secured with tape (you can see clearly why 8 or 12 tabs may be better):

Image

One of the cardboard rings had double-sided tape applied to one face - what will become the outer face - and the solar film will be stuck to this. The 4 tabs of the tube had double-sided tape which meant that I simply had to centralise the ring and the basic filter cap would have been formed. The use of double-sided tape was probably not the best idea - but it was quick and wasn't messy.

Image

The protective tape was removed from the double-sided tape and the basic filter cap was inverted and placed onto the solar film which was lying flat on the table:

Image

The external surface of the filter cap was covered in double-sided tape and the solar film cut with about a 1cm (½") margin and folded over the edge and onto the tape.

A second net for a cylinder is drawn out, but this time with many small triangular-shaped tabs. This second ring reinforces the walls of the filter cap and also secures the solar film:

Image

The second cardboard ring had double-sided tape applied to one face - the inner face - and then stuck onto the exposed tabs. With hindsight, this was a problem as the double-sided tape wasn't strong enough and as the cardboard of the tabs unbent (as cardboard is wont to do), it meant the second ring wasn't stuck down securely. I had to revisit this using super-glue (cyanoacrylate) later on, which is both messy and will stick the flesh of your fingers to anything you touch. To stick cardboard, apply the super-glue to one surface and a drop of water to the other surface - press together and Bingo!

Image

This completes the basic filter. However, it didn't look too fancy, so I planned some further reinforcement and a fair amount of 'tarting up'!

I planned to use Duck tape for this - but only had black. Whilst this would match the dew shield of the RACI finder, being used in strong sunlight I guessed it might cause problems by absorbing heat from the sun and possibly softening the glue on the double-sided tape. So, off to B&Q to get some silver (= heat reflecting) tape...

Image

A close-up of the completer solar filter in situ:

Image

and finally, a picture of the completed solar filter in place on my RACI finder (and the scope sporting its solar filter too):

Image

As has already been mentioned by James, you need to filter the OBJECTIVE end of the telescope and not the eyepiece end as this stops the internals of the scope overheating and possible melting the Canada Balsam glue between lens elements in a refracting telescope.

Now, instead of using the "no shadow" technique of aligning on the Sun, I can look through my RACI finder!

Hope this helps,

Kind regards,

Art
Last edited by arthur dent on Fri Mar 02, 2012 11:33 pm, edited 1 time in total.
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RE: Solar Observing

Postby philip pugh » Thu Aug 25, 2011 12:13 pm

I'll third or fourth the Baader filter suggestion. Although the sunspots are quite difficult today, there has been quite a lot of solar activity and I'm taking snaps in "white light" as well as hydrogen alpha.

WARNING: Observing the Sun is extremely addictive and can result in the purchase of several hundreds or thousands of pounds worth of equipment. It can also attract the attention of passers by who think it is strange to be out with a telescope or binoculars in daytime.

Extreme solar addiction can lead to problems with partners and employers and can lead to medical side effects. For example, if I don't see the Sun in a week my eyelids start twitching.
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RE: Solar Observing

Postby kevr » Sun Sep 04, 2011 11:53 pm

I have to confirm the addiction....I have an Astrozap filter that uses Baader Solar film and has led me to sketching what I see using the S@N solar observing form.
I now get home, and one of the first things I do is look at SpaceWeather.com...and yep...saving up for a Ha 'scope as well!
Addicted!!

cheers
Kev
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RE: Solar Observing

Postby mavrickxxx » Fri Sep 16, 2011 10:16 pm

What a facinating subject. I was on ebay looking at solar filters and thought it would be a great thing to own but the price is a bit sore to swallow lol. But the film and DIY solution is brilliant. Plus i never thought about putting it on binoculars. Worh a try i think.
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RE: Solar Observing

Postby mjpfc » Sun Oct 09, 2011 5:13 pm

Living in Blighty, it is vital that we use the whole of each 24 hours to do some observing especially as the clouds have a nasty habit of rolling in as the sun drops after cloudless days. SOLAR veiwing helps to do just that as well as bein fascinating in iself.

I have BAADER filters for my Newt, My reflector, Binos and a pair of solar glasses as well as a Coronado PST.
IMPORTANTLY, The more filters you have, the more organised you have to be in checking them thoroughly before each use. The consequences of a pin hole or other defect could be immediate and permanent.

I will always look in white light, the PST is an incredible instrument and shows tremendous detail but only tells half the story.

Clear Skies, Mick IOW
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RE: Solar Observing

Postby smerral » Sun Oct 09, 2011 9:56 pm

Another addict here. I have had a PST for a couple of months and have recently bought a Ca-K diagonal..so that's a cool grand spent, and it's stayed cloudy since I got it and I'm DESPERATE to see the sun!!! So be warned!
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