Eclipse of the eyes

On Monday, August 21, a total solar eclipse will cut a 70-mile wide diagonal path across the country starting from Oregon and ending South Carolina. While we won’t be able to see the total phase of the eclipse here in Stockton, we will get a partial eclipse that will cover about 78% of the sun.

It is important to note that to view a solar eclipse one must use special eye protection or risk serious damage to your sight including blindness. Regular sunglasses won’t do.

For the last eclipse in 2014 I made a filter out mylar, which is a paper thin polyester coated with a metallic finish, for a 200-400mm telephoto zoom lens.

The lens has a front end diameter of about 110mm (about 4.3 inches), far too big for a conventional filter. Instead, the lens employs what’s called a drop-in filter, which is smaller (52mm) and fits into a holder that slides into a slot near the rear of the lens. I had made a filter by fitting mylar over a spare drop-in holder but I wasn’t totally satisfied with my results. The material scattered the a light a little too much but more importantly, sliver color of the mylar left my images looking bereft of color.

I have seen photos shot with a black polymer filter which gives the sun a nice orange hue, but those filters can cause a couple hundred bucks. A bit expensive for shooting something that only occurs every few years. I decided to try to make one myself.

A black polymer sheet, which is paper thin, transmits only 1/1000th of 1% of light through it. They too are a bit expensive, about $30 to $60 for a single 12”x12” sheet. Being a self-avowed cheapskate, I tried looking for another way.

I had a pair of eclipse viewing glasses leftover from the last eclipse. It has a thin cardboard frame (like those old 3D movie glasses) with the black polymer lenses.

I cannibalized the rectangular lenses but at about 1-1/2” x 1”, they were far too small to cover the front of the large lens. The solution was to adapt the round mylar filter that I had already made.The problem was to how to make a square peg into a round hole. I cut a rectangular hole in the mylar filter and simply taped the polymer lens into it.

I took a few test shots of the sun with the new filter and reviewed the images on the camera’s monitor. They were perfect. The sun appeared as a bright orange orb against a field of black. 
I lifted the camera to take more test photos to make sure. After a few more frames, the viewfinder was suddenly filled with a blinding white light. I quickly pulled away from the camera to avoid injuring my eye. I knew that the filter had failed. Pulling it from the slot, I saw that there was a pencil eraser-sized hole in the center. Because the filter was near the focus point of light, that created enough heat to melt the filter, much like using a magnifying glass to start a fire. The mylar was able to reflect enough the heat for it to stay intact, the black polymer was not.

Much the same thing can happen to your eyes if you look at the sun or eclipse without protection. It can seriously damage your retinas.

I broke down and got a bigger sheet of polymer for the front of the lens. It was a smaller piece (4.5” x 5.5”) so it only cost $13.50. I fashioned filter out of it and cardboard from an old shoe box and it fit nicely over the end of the lens. It’s not pretty, but I did some test shots with it and it worked and held up well.

The Stockton Astronomical Society in conjunction with Delta College astrophysics professor Lincoln Lee will be holding an eclipse viewing party at Delta starting at about 9:00 a.m. (the peak will occur at about 10:21 PDT) They will have a number of telescopes equipped with filters, indirect viewing devices and eclipse glasses. A solar eclipse is a fantastic celestial event to witness, just make sure you have the proper eye protection to view safely.

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    Clifford Oto

    Clifford Oto, an award-winning photographer, has been with The Record since 1984. Through the changes from black and white to digital photography, he’s kept his focus on covering the events, people and life of San Joaquin county. This blog deals ... Read Full
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