solar observing

gjrwood · Post by **gjrwood** » Sun Jan 29, 2012 1:58 pm

My telescope is a skywatcher 130m, can I use this scope to view the Sun using the correct filters and if so what filters do you recommened?

David Frydman · Post by **David Frydman** » Sun Jan 29, 2012 2:09 pm

Welcome,
Initially I would stick to observing Jupiter, The Moon, Venus, Mars ,Saturn and the objects in Orion.
Also the many other night time objects.

Others will advise regarding the Sun, but great care is needed here.

Regards, David

Brian · Post by **Brian** » Sun Jan 29, 2012 9:08 pm

Hi, and welcome.

Yes you can use your 130m for solar observation by fitting it with a full-aperture solar filter such as one made with Baader Solar Safety Film (ND=5). You can buy the film as a sheet and make up a filter to the instructions provided with the material, or you can buy the filter already made up to the correct diameter to fit the aperture of our tube. Have alook here for instance:

http://www.firstlightoptics.com/solar-filters.html

Firstly though I recommend you read through the advice and warnings given under the "Solar" section link at the top of this page. If you have a finderscope, make sure it is capped off before you observe, and use the shadow of the telescope itself onto the floor to line up with the Sun. Whatever you do, DO NOT use a solar filter which screws into the eyepiece unless the full-aperture solar filter is also in place. The Sun will not give your eyes a second chance.

That's a start, hope it will help you. Feel free to ask,

Regards,

dazcaz · Post by **dazcaz** » Sun Jan 29, 2012 10:55 pm

An easy option that I was shown but yet to implement is to not use a full aperture filter but use the cap that comes with the scope. These usually have a smaller aperture with a removable cover.
Take a piece of solar film and stick this inside the cap over this aperture.
Make sure it's stuck very well and completely covering the hole.

You do not need full aperture for observing the sun so the smaller aperture is more than enough. As you usually buy the film in A4 sheets, this option gives you more filter to use on other projects

Always inspect the filter BEFORE looking at the sun through it. Any damage at all replace it with the stuff you save by not going full aperture

Others will shout STOP if what is written above is wrong

brian livesey · Post by **brian livesey** » Mon Jan 30, 2012 10:58 am

An advantage with a PST is that you could have it modded to fit onto a bigger refractor.
This needs to be done using great care and with the proper instructions.

David Frydman · Post by **David Frydman** » Mon Jan 30, 2012 11:52 am

Brian,
I think the PST makers did something to make modification more difficult although I cannot remember the details.

Regards, David

brian livesey · Post by **brian livesey** » Mon Jan 30, 2012 3:50 pm

It seems that they ran LOCTITE into the threads of the objective tube to prevent its removal from the main body; although it didn't stop the determined.
I've since heard that the makers have stopped doing the procedure, but I wouldn't guarantee it.

Brian · Post by **Brian** » Mon Jan 30, 2012 10:11 pm

dazcaz wrote:
You do not need full aperture for observing the sun so the smaller aperture is more than enough.

True but resolution goes with aperture, and the more aperture you use the more detail you can see in the sunspots. Otherwise why go to the trouble of making a full-aperture solar filter for a 40inch dob

:

David Frydman · Post by **David Frydman** » Mon Jan 30, 2012 10:31 pm

Saw this a few months back.
I thought it daft then and daft now.
From memory a German amateur's scope although I may be wrong.
If there was a catastrophic failure of the thin film such as a bird flying at high speed into the scope the observer would probably have his eye instantly and permanently disabled.

Yes, it is a funny astro picture and worth a laugh, but newcomers should be in no doubt how fast permanent eye damage can occur when using optical aid viewing the Sun.

And looking at the Sun with the unaided eye will also cause damage, except for the accidental glance where the eyelid response is fast enough to keep you out of trouble. Perhaps a tenth of a second.

So to any prospective Solar Observer please read all the advice under Solar section at the top of the SPA page.

Anyway no joy for me with the PST as cloudy in the morning and midday also no observations.

Regards, David

dazcaz · Post by **dazcaz** » Mon Jan 30, 2012 10:34 pm

Holy S***!!!!! OK point taken!

For most of us full aperture isn't necessary, but for some every inch counts

The typical dedicated solar scope is only a couple of inches across.

I'll stick with trying the smaller aperture idea... looks a bit cheaper and less easy to damage

David Frydman · Post by **David Frydman** » Tue Jan 31, 2012 9:39 am

The possibility of a bird strike reminds me of British Rail I think who wanted to test their new High Speed train.
They did not have the necessary equipment so asked to borrow I think NASA's test rig.
The test rig arrived and they set it up and loaded the chicken into the cannon.
The bird flew at high speed, smashed through the HS train windscreen, through the back of the driver's seat and imbedded itself in the rear wall of the cab.

The alarmed testers contacted NASA and on being quizzed revealed that the chicken had still been frozen.
The test rig was meant for a standard chicken not a frozen one.

Bird strikes are common in aircraft having recently brought down the Miracle in the Hudson Airbus and a Red Arrows Hawk I think.
It also I think caused a Caravelle aircraft I was on to lose an engine at a very low altitude climbing out of an airport. The Finnish pilot Captain Makinen brought the aircraft straight back for a very high speed landing with a full fuel load. It was perfect but the disabled engine sounded awful.

So in a rural situation where the large scope is pictured with the full aperture solar film a bird strike is a possibility.
A pigeon flying at 35 mph would probably go straight through the film.
I have had quite a few birds crash into windows. They usually bounce off if small but a pigeon shattered our window.
Also a pigeon and a sparrowhawk chasing it went straight through the skylight of our local library when i was there.

I think that amateur astronomer is foolish to use such a large scope with solar film.

Regards, David.

brian livesey · Post by **brian livesey** » Tue Jan 31, 2012 9:58 am

The film looks stretched too, which affects definition. SolarFilm should be "relaxed" in its cell.

Kevvek · Post by **Kevvek** » Thu Feb 02, 2012 7:29 pm

Hi, hope you don't mind me butting in, but I use an astrozap full aperture baader film filter on my Megrez110. It's a fast refractor and just wondering if I would see any benefit in making a cover to fit over the filter to reduce the aperture. I think I'm right in saying that it will also increase the focal length of the scope.

cheers

Kev

David Frydman · Post by **David Frydman** » Thu Feb 02, 2012 7:40 pm

Dear Kev,
Your Megrez 110 will be a high quality scope. I presume it has ED glass.

I don't think you should reduce the aperture, but if you do only to 100mm or 95mm.

The advantage of high quality optics is that they are designed well.

However, The cooling properties of fast refractors make them more prone to temperature effects on the image so I would think the time you left it out, how it stabilised etc can only be found by trial and error.
You obviously store it indoors and in dry not humid conditions so it will need to cool maybe 20C at present.

You could make simple masks but in good conditions I think only minor reductions if any are needed.

Others who use these scopes for solar work may give better advice.

Regards, David

The focal length remains the same.
The focal ratio gets larger, which is where any quality improvement comes in.

It is like stopping an f/5.6 camera lens to f/8 to get better images.

However, your scope is designed to work at full aperture, whereas camera lenses usually need 2 or 3 stops stopping down for best star images or any images.
A 50mm f/1.4 lens usually works best at f/4 but high class aspherical 50mm lens have been made to give good images at full aperture even f/1.2
A 300mm f/ 5.6 usually works best at f/8 or f/11.
The wartime Dallmeyer 36 inch f/6.3 aircraft camera lens that did most of WW2 high level photography works best from f/8.7 or less.
So each lens or scope is different.

David Frydman · Post by **David Frydman** » Thu Feb 02, 2012 8:23 pm

The Megrez 110 seems to be an air spaced doublet ED so called APO.
655mm focal length. f/5.95 say f/6.
I don't think you need to stop it to slower than f/7 and you could try f/8.

So you could try 95mm and 85mm stops to see if it makes a difference.

The only way is to try it and see and note temperatures and cooling times.
And of course the Seeing conditions.

Regards, David