Photographing Solar Eclipses - Large Telescope
Author: Bill Kramer
Last update: Saturday, 18-Apr-2015 18:52:31 EDT
Using a Larger Field Telescope
Using my simple rule of thumb, a larger field telescope is one with an aperture of 5" or more. Another way to think of it is a larger telescope cannot be easily carried out to the drive way or yard in one load. Despite the difficulty in transporting a larger telescope, the views and photographs can be very worthwhile. Or so I have heard. I must confess to having never brought anything larger than an f/10 4.25" reflecting telescope. That was for the 1972 and 1973 eclipses viewed from on board ships. The view was excellent using a 1" eyepiece (about 45x). For subsequent eclipses I've used a Questar telescope and binoculars. I can only imagine what it looks like through an eight inch (20cm).
Larger telescopes tend to have longer effective focal lengths and may not show the entire ring of the moon. They are best suited for looking at the chromosphere, corona streamer details, and prominences. Or you can attempt to see stars behind the corona near the sun. For scientific studies these telescopes are essential. I just can't say that they are recommended for the few minutes you have available under the umbra. My favorite views of the eclipses I've seen have been through smaller telescopes that showed the entire moon and a lot of corona in the same field of view.
An f/10 8" Schmidt Cassegrain has an effective focal length of 80" or 2,000mm. This is about the maximum focal length that can be used to photograph (35mm film) the entire lunar disk and still see some of the surrounding solar atmosphere. A 35mm camera will barely hold the lunar image hence very little of the corona can be photographed. On the other hand it is possible to image stars through the corona, do spectral imaging, and obtain close up views of prominences in white light.
"Light buckets" or very large telescopes are not needed for a total solar eclipse. The corona is very bright and you will not be interested in deep space objects during the eclipse event. I can imagine that very large apertures will diminish the quality of the view and unless you are engaged in scientific studies requiring such optics (such as detecting gravitational effects of starlight near the solar disk - use radio waves and go enjoy the eclipse!) The expense of bringing very large optics along may not be worth it. For the ease of travel and best view, a smaller telescope is the winner. The next best solution is a good pair of binoculars.
Perspective: The 1991 total solar eclipse path crossed over some of the largest telescopes in the world located in Hawaii. There was a documentary showing the preparations and other scientific work the observatory astronomers were engaged in at the time. My favorite scene from this documentary is when the astronomers all run out of the control booth during totality to view the eclipse through a 3.5" Questar telescope.