August 21, 2017 was a big day for most of the country with a very rare total solar eclipse visible across much of the country.
In Cary, North Carolina, we only achieved about 95% of totality, but it was still an opportunity to test some basic optical principles and photography skills. So I set up a pair of 10x power binoculars as a projector and was pleasently surprised at the details I was able to photograph.
Even from the first photograph, a line of sunspots could be seen across the orb. The gear is nothing special. All of these photographs are of the image projected through the binoculars onto a white piece of paper and are taken with a Nexus 6 smart phone.
About half way to totality, a strange redness in the sky was obvious to several of us observing the event. Despite the short shadows from the midday solar position, the sunlight appeared as if at the end of the day. A significant diminishment of the radiative energy was obvious, too, and everything felt much cooler despite the continued glare.
2:44pm was the maximum pnuembra (shadow) for the photograph above. You can barely see the last sunspot grazing the edge of the moon’s edge.
This was a five minute setup. The binoculars were screwed onto a cheap tripod and a large piece of foamcore board was hurridly cut to fit over the objective ends to create a shadow on the observation board. Gentle re-adjustment from time to time re-centered the image to maintain maximum focal clarity. This photo is from early in the event, and we later adjusted it to place the observation board on the ground so the projection was larger and focus more finely adjusted. (The golf umbrella and chair in the background were never used, the event was too exciting to sit down!)
Shadows during solar eclipses are curious. Tiny openings between the leaves of trees act the same way the binocular setup works and effectively project the sun’s image onto the ground. The only difference is that the binoculars use lensees to magnify the image with a short focal length and the tree “pinholes” magnify the images according to the proportion of distance of the hole to the ground.