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[Chicago Astronomer - Astro Joe]

Homemade Solar Filter project for the 152mm Refractor
15 March 2024

As the big eclipse date approaches, solar equipment is getting harder to get and much more expensive - supply and demand.

As early as summer last year, I was looking for a full aperture solar filter for my 152mm monster refractor scope, but not having much luck. Metal ring filters were either too small or much too big...and the one some did have, was the exact diameter of the Dew Shield.   No good.  With plenty of time before the eclipse, the urgent need was pushed back for other matters. But, the new year brought the need back to prep and I continued the search for full aperture metal ring filter, but again...none suitable for this scope.

Some criteria first....

I prefer the "Baader" type of mylar solar filters.

First, Glass filters (above) are fragile heavy and easy to scratch. And the surface of most glass filters are not optical high grade quality, with imperfections....and glass filters are expensive. I have had a glass filter n the C11 scope, and the thin surface layer of the filtering had flaked off.

Second, I am not a fan of those filters that produce the Orange-type of filtering. They do the job ok, but cut-off the higher frequency of the blue light...

With the Baader-type of natural color filters, the image is more sharper and easier to work with.



Ideally, I desired a full aperture metal ring filter that would fit the 152mm...a pretty big area to cover...

But, no luck.  

I decided to make my own, as I could get a perfect fit and a whole lot economical.

I ordered full sheets of the Baader film and got my materials ready.

(Side note: I ordered the sheets from a reputable retailer and they sent it out the next day, but the US Post Office  kept sitting on it.   Day after day, I would get a message that the package was "Being processed".  For over two weeks this was delayed and I was concerned that it would never get here...



So, I ordered another package from a different reputable retailer and it arrived within three days...



A week later, the first missing package arrived - three weeks after the order.  No excuse US Post Office... )

Now, with plenty of solar film at hand, I started to construct my first prototype for the 152mm.  The housing would be Dollar Store Foam board, four layers in thickness, two to grab the tube in a friction fit and two to sandwich the film.  I used a radius cutter for the opening...






I wanted this filter holder to be flat, with out the protruding sleeve that would fit around the tube.  Using a sleeve would produce storage problems...like this example...



Using spray adhesive, I mated the foam boards together and carefully applied the adhesive to the film, bonding it to the board.  I used small velcro strips along the outside of the tube and inside diameter of the board, making a good friction fit, secured with the velcro.  One needs to quickly remove the filter at Totality and replace it in a smooth action after the diamond ring effect.  In tests, the filter housing was strong, stiff and came on & off with satisfied results.



A good test on how well this filter housing would stay on would be our Chicago Astronomer solar session, where the winds would gust 25+ miles an hour this day.    It certainly was extremely windy, but the filter housing stayed put and did not fail.   Views were excellent, displaying a nice white light solar disk with Sunspots and granulations in it's natural white light.



This high wind acid test passed and instead of this being just the prototype, may just keep it as is, dedicated for the 152mm Refractor.

Satisfied with this technique and performance, I need to make a dedicated one for the 100mm Maksutov scope and others, including cameras and finder scopes.

Astro Joe