Solar FIlters
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All of these filters were created out of a single A4 sheet of Baader solar film from Astro-Physics.  I've included hints and tips that made things easier for me.

Construction Basics

The Baader film comes with an excellent set of instructions, but I'll review the essentials.  You'll need to create three basic parts for each filter:

  1. Outer cell:  The part that faces the sun and holds the filter.
  2. Inner cell:  Similar to the outer cell, this is a ring that holds the filter and fits inside the ring.
  3. Ring:  This is the part that fits around the outside of the tube.   It must fit snugly and be stable.

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The Baader instructions show ring construction as layers of poster board.  After some experimentation, I found that a heavy ring and a thick inner cell made for wide gluing surface and a more sturdy unit.  (Dimensions exaggerated above.)  I also offset the cells to make the outer cell the "stop" for solar light.  The inside hole of the inner cell didn't need exacting attention, so it was easier to cut.


Hints & Tips

1.  Cutting Circles:   I used a drill press and circle cutter (commonly used for cutting mats in picture frames) to make the inner and outer rings. 

2.  Materials:  I've used brass, cardboard, hardboard, and CDs with good results.  Feel free to experiment with other available materials.  The critical properties of the cells and the ring are to hold and protect the filter.   Use a material that you are comfortable manipulating.

3.  Air:  Make sure to leave some space between the scope and the ring to allow for air to move.  Otherwise, you may end up tearing the filter material.

Draco Kit scope

This was the scope that got me started.  The kit is made of a simple lens element, PVC pipes, and a film canister eyepiece.  The filter cell is wrapped paper (ala the Baader film instructions), which seemed too flimsy for regular use, in my opinion.  This is the only filter NOT made from the single sheet of Baader film.


TableTop 76

This was my first experiment in making a cell for the Baader film.  I chose cardboard as the medium, since it was cheap, easy to machine, and soft (compared to the filter material.)  Brown packing tape "finished" the outside and hold things together.

While this scope has a very small aperture with a relatively large secondary and is considered by many to be a toy, it's a very portable and convenient scope for quick solar observing.  Since the object you're viewing is incredibly bright, the small aperture does not affect image brightness.

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This is the inside of the filter for the TableTop 76.  The filter material is a bit too loose, but the glue sets quickly and I could not adjust it.  It does not seem to affect the view.

The ring is a chunk of shipping tube that was just a bit bigger than the TT76.   The black strips are pieces of felt.  They serve two purposes - to make a snug fit and to allow air to exit the filter as you push it in.


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This is perhaps my prettiest filter holder.  The ring and outer facing are made of brass sheeting.  The outer facing was difficult to cut and took three tries to get it right.  The ring was bent 90 degrees to provide a gluing surface and is relieved with "v" shaped cuts to make forming the circle much easier.  The brass pieces are glued with epoxy.  (Previous tests with solder did not prove successful and discolored the brass.)

On the inside view, you can see the felt pads added to the ring to prevent scratching the scope.  There are three channels to allow air to escape. 

The filter is held in two cardboard cells with the film glued in between.  The cells are lightly glued to the brass front ring.  The tension isn't quite right on this cell (it's a bit tight, causing side-to-side wrinkles), but it does not affect the view.

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SkyWatcher 102

Since this is the scope that I'm most likely to grab for a quick view, I wanted something easy, yet different.  The results are (I hope) unique, yet easy to do.

The inner and outer rings are software CDs that I no longer needed.  I used double sided tape (or spray adhesive) to attach the CDs to a block of scrap wood so I could cut the circle with my drill press circle cutter.  I really like the look of the multicolor-silver CD holding the silver filter material.  It contrasts nicely with the dark blue scope.

The scope has a ring of Velcro loops near the aperture that I use to attach focusing masks and the solar filter.  It's key to ensuring that the filter stays in place.  Three "hook" tapes extend from between the two rings to firmly attach the cell to the scope.  A strip of foam makes the light seal.

I use a double CD case to store the cell.  You can see in this photo that three short dowels extend from the inside right to better lock the filter in place.


Orion XT8

The most annoying thing about solar observing with Newtonian scopes is that your eyepiece is at 90 to the bright solar light.  With many eyepieces, the bright solar light ends up making it difficult to see the dimmer image behind the filter.

I decided to make another unusual filter cell for this scope.  The actual filter is a small three-inch, off-axis filter.  The cell extends off the side of the scope to provide shade for the observer's eye.  There is a hole for the finder (properly filtered, of course), since this cell hides the scope's shadow.  This is still a rough work-in-progress.


Photos to come.

Protecting your Filter

After spending all that time making your filter, you'll want to protect your filter.  There are some keys to protecting a film solar filter:

1)  The film is tough, but can easily be ruined by scratches or pin-pricks that allow the sun's power to shine through.

2)  The filter should not be distorted, stretched, strained, or crushed.

3)  The ideal filter  holder should firmly, but gently hold the cell, but not touch the film.  It should be mostly air tight to prevent moisture infiltration.

I use a plastic sealing container that comes close to the size of the filter.  I pack tissue paper around the sides to keep the filter in place.  For example, my brass filter for the FS-80 is shown at right: