Photographing Solar Eclipses - Small Telescope
Author: Bill Kramer
Last update: Saturday, 18-Apr-2015 18:52:20 EDT
Using a Small Telescope
There is nothing that compares with the view of a total solar eclipse through a telescope. It is like the difference you experience of looking at the moon with just your eye and then a telescope. It doesn't really matter what size of telescope you are using - the view is very different. With a telescope the craters and mountain ranges are revealed and the moon takes on a very different appearance. The view of a total solar eclipse through a telescope is much the same. Prominences are amazing and the corona simply fascinating.
Unlike most astronomical uses of a telescope you do not have a lot of time to study the object in the eyepiece. You most certainly do not have much time for changing eyepieces or inserting a barlow lens. That said, I confess to having done both. Before the eclipse I practiced doing the same with the telescope by looking at the moon, memorizing the twists of the focuser, and perfecting the 'no look' rapid change of lenses. The Questar telescope is marvelous at this task with the built in barlow lens. All that is a required is a flick of a switch to swing the lens into place and a twist of the focusing knob.
I found the best views to be with a wide field eyepiece, 25mm or larger. You can see plenty of detail and still get a good overall view as the scene slowly changes. Looking closer you can see the prominences slip behind the moon's edge or appear against swirls in the corona as totality takes place. With the wide field eyepiece of the Questar (32mm) the magnification is approximately 40x and the angle of view about 1.3 degrees. The moon's half degree size fits comfortably, the prominences pop out in an almost 3D fashion, and the inner corona glows with neon threads twisted around each other - it really is something to behold.
When visiting another hemisphere (for me, going South of the Equator) a small telescope is a lot of fun if you get a chance to do some night time observing. Bring along an atlas or sky map to help navigate the new and unfamiliar sky looking for the 'best of' with the telescope - it really is worth the hassle of carrying it along in most cases.
But what about photographing an eclipse with a small telescope?
First off, let me define what a small telescope is from my perspective. Small telescopes are those with an aperture of 5" (12cm) or less. A popular term for a small telescope is a "grab and go" scope. The type of telescope you can quickly carry out into the night for a fast view of a planet or the moon. Folded optics make for very compact and portable telescopes although small refractors should not be ruled out. If it can fit in the overhead storage of a modern airplane then it is a-okay for eclipse chasing.
When using a small telescope and camera, a good mount is essential to get good photographs and to enjoy the experience overall. There have been many cases where the tripod was forfeited to allow for packing something else only the render the telescope useless or frustrating to use during the eclipse. You can gamble that you will find a table or some other platform to set up on but in my experience that is not recommended as you will most likely miss out on viewing the eclipse itself.
During totality a small telescope will yield fantastic views and photographs of the inner corona, prominences, and chromosphere. You can see great detail in the prominences and short exposures will yield beautiful pictures of this phenomenon. Using fast film such as ASA 400 or a good digital camera, exposure times should range from 1/500 to ½ second in time. Longer exposures to reveal the outer coronal structures are possible. Longer exposures also bring up tracking problems as the Earth's motion is greatly amplified by the magnification. This problem is solved by using an equatorial tracking mount and many smaller telescopes provide the perfect solution with a built in drive.
Computerized mounts provide a nice way to track objects in the sky once properly aligned. During the day light hours only the sun will be visible and some systems require stellar sightings for alignment. You can either set up the night before or accept the initial locations as okay without verifying. When used with photography a computer driven mount will be fine so long as the telescope and camera are well balanced, do not put too much stress on the drive motor, and the exposures are relatively short. Longer exposures are not needed during a total solar eclipse thus field rotation will not be an issue. It is highly recommended that you practice by taking pictures of the moon when it is at about the same altitude in the sky. This exercise should reveal any problems your mounting system could encounter.
When preparing to bring a small telescope for photography purposes, be sure to figure out some way to get in some observing with a moderate power eyepiece as well. My favorite magnification for viewing an eclipse is at 40x to 50x. At that power one can see the corona and prominences all at once and a great amount of detail is visible that you cannot see with binoculars and the naked eye. You will not have much time for this luxury and I should note that sharing the experience is almost impossible except during very long eclipses of 4 or more minutes.
1991 Total Solar Eclipse - Baja Mexico - Questar prime focus (~1350mm)