Solar Filter for Celestron 21024 Telescope

We like sunspots down here on this radio ranch!  They make our little radio messages go further on the shortwaves as all the sunny goodness cooks the earth's ions to make the radio waves skip along way over the horizon.


So even the radio rancher needs a new work shirt and pants from time to time, but hates shopping for them.  The radio wife coaxes me to the store with a "...Okay, you can pick out a toy if you come with me to the store only if you are good."  Well, I guess I was good that day and found this little telescope! 

The tiny Celestron FirstScope 3.0"/76mm Reflector Telescope Kit turned out to be a fun little toy.  They designed it for the "2009 Year of the Telescope" It was a device to get people interested in astronomy and in my opinion this is way better than any department store telescope I remember.  Good job Celestron.  The views of the moon and planets are quite impressive.  But pick up a good 2x Barlow lenses to use with this little guy.  Also, better eyepieces are also on the list - but for $40 you can get a few accessories. 

I thought it would make a great solar telescope to see what those little back spots on the sun today really look like.  They do not have a solar filter but as it happens, we figured it out for you down here on the Radio Ranch...

These are not the best astrophotos of the sun you'll ever see.  I simply put the camera to the eyepiece and shot a couple macro shots.  What really impressed me is the fact the white light filter Baader Filter that  I used shows the sun with this inky black background.  You can really get the since that this is really a star!  You can clearly see sun spots #1381, #1382, #1383 and  #1384 were visible today.  Awesome, sublime, cool!

The telescope kit comes with a ND filter so it makes some of the other details (besides sun spots) visible. You know,  like sunglasses make things better?  It looks more blue in the photo but looks more star-like through the eyepiece.

Here is what NASA saw today as well. 12/23/2011.  www.spaceweather.com

Let's build one!  To filter out the sun's light there are several types of filters you can choose from.  I picked the BAADER AstroSolar™ Solar Filter Material which was apparently was developed at the Baader Planetarium for viewing eclipses.  There is at least one supplier that will sell some smaller pieces. I choose the 3" x 3" for approx $9.00 USD. 

Baader AstroSolar Film (Visual, ND 5):
http://agenaastro.com/baader-astrosolar-film-visual-nd-5.html


BTW - do not use an "eyepiece solar filter"  They are dangerous as they can heat up and crack and should not be used on a reflector type scope in any case as all the light gets focused on the secondary mirror.  I also found the glass filters are actually prone to getting scratched and this lets too much light in. 

Also, during my research I saw that some silvered mirrors can be used, but the ones I tried don't let in any light.  I think you need some of that 2-way glass mirror and have to cut it to shape ~ I will try this one day ~ it should work well in my filter holder.

To start we need a way to hold this material.  It is a thin aluminized Mylar film so we need to construct a cell to hold it.  The film come with a way to do it with some cardboard but it looked way to flimsy to me. I wanted a more solid looking approach.

After some searching I found that an ordinary coffee can fits nicely on the 3" scope.  This one is made out of cardboard with a foil lining and a tin ring for the lid.  Eight #4 screws and nuts hold the cell to the tube by the rim.

I had a couple of fiberboard rings fabricated as well.  ( I will upload the drawings for theses later)

Measure twice.  I wanted to have as deep a cell as I could so the possibility of accidentally knocking the filter off was almost nil.  An inch and a half will do, it is also the width of my tape.

Using a technique for cutting tubes I learned for making model rockets, use some tape to make a straight cut.

I thought this can's artwork would be cool, but I found that the paper artwork was slightly glued on and fell off.  I put a layer of 1- 1/2" gorilla tape on instead that gives it a nice textured look as well.

Toughest tape ...in the world!

A drill press really helps here.  Since this is tinplate around the rim it can distort if you are not careful drilling,  Also there is not much room on the ring and we need to make these holes as neat as possible.

I carefully drilled 8 holes into the rim of the can using the rings as a guide.

Ready to assemble,  The idea is to sandwich the filter into the cell between the two rings and attach the filter to the tube with several screws and nuts.

My material came with this little wrinkle in it - does not seem to hurt it,

The technique that seems to work is to apply glue to one of the rings.  Place the filter on a paper towel, and drop the ring onto the material.  You need to be careful not to stretch the material.

After it sets up line up the second ring and punch the holes through.  Slide the assembly unto the tube.

Carefully, slip in the screws and a washer ( not shown)

Then using a alternating criss-cross pattern tighten up the screws while holding the nuts from the back side.  Be very careful for two reasons: First the tension must be even on the film so if one screw is too tight it will pull the film.  Secondly, the film is vulnerable to getting punched so be careful with the screwdriver! 

Fits like a glove!  Looks pretty cool too IMHO. It has that astronomical instrument look eh?

As a bonus, you use the can's plastic lid as a protective cover! The next thing to do is take a black Sharpie permanent marker pen ink pen and hold the filter up to the sky.  Blot out any pin holes you see from the back side with the pen.  It works best with a nice fresh pen, I also colored the edge of the cut can as the cardboard was exposed. 

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