Solar filter made from lenses of polarized sunglasses

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SilkWorm New Member • Posts: 21
Solar filter made from lenses of polarized sunglasses
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Note: Please use your own judgement about the absorbance of the resulting light filter, This method may not be safe for naked eye or SLR view finder. Use this method on your camera at your own risk.

If you are looking for the last minute purchase of solar filters for the solar eclipse event on 8/21, they are likely all sold out or too late to ship. Today I tested a homemade solution of using two stacked polarized filter to achieve and absorbance of 3.5+ or about 12 stops or attenuation. If you have a pair of (linear) polarized sunglasses whose lenses are detachable, this might work for you. You just need to stack them perpendicularly. The working principle is here if intereseted: http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html. Since the resulting attenuation varies from quality of the polarizing lens, cautions should be taken.

You need to take off the lenses and stack them like this, with the aid of Scotch tape. Adjust the angle until maximum attenuation is achieved.

I have access to a UV-Vis spectrometer, so I measured the absorbance. The red curve is a single lens and the blue is the cross-stacked filter. As seen the blue curve is very intense and noisy, because the filter basically blacks out most light and fall outside the dynamic range of the spectrometer (about 3.5).

And here is the "Scotch tape mount" on the Lumix 45-150 zoom lens/GX85 body with a sample picture and video. The sunspots can be seen with proper focus. With my particular pair of sunglasses, I can manage to shoot at 150mm at f22, 1/1000-1/4000, but your miles may vary. Also a tip when shooting still photos, use the option of "Preview Aperture Effect." This way the aperture will be closed down during framing, so it's easier to focus and reduce the chance of burning the sensor. Another tip for video is to use the "Ex. Tele Converter" function on Lumix bodies. Since 150mm cannot fill the frame with Sun anyway, I shot in VGA and got extra 4.8x zoom: 1440mm equivalence focal length.

Cropped Image.

Sample Video:

https://youtu.be/XFlUsN3mQjc

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