Imaging a Solar Eclipse
Viewing and photographing a total eclipse of the Sun.
The human eye is superb in its ability to discern and resolve a wide range of brightnesses and details during an eclipse from the diaphanous, faint wisps of the outer corona to the fine, hairlike structures in brilliant prominences. However, with the advent of high-speed, ultrafine-grain film and high-resolution video cameras, it's an ethereal scene almost anyone can capture using only modest equipment.
Choosing the Right Equipment
The type of camera lens you should use depends mainly on what you want to record. For wide-angle shots of the sky with a film camera, a standard 50-millimeter lens is all you need. Although it gives only a minuscule (0.5 mm in diameter) image of the Sun on film, it is well suited to capturing the surrounding sky with Venus, Mercury, and possibly a few bright stars. For dramatic effect, try to include foreground objects in the scene. Fisheye lenses can capture the whole sky and are especially good for documenting the approach and retreat of the umbra (lunar shadow) and the 360° sunset twilight colors that ring the entire horizon.
For close-up shots of the eclipse's partial phases, Baily's Beads, diamond rings, chromosphere, solar prominences, and inner corona, you'll want a lens or telescope with about 2,000 mm focal length. This produces a solar image approximately 18 mm in diameter, which nearly fills the frame of a standard 35-mm camera. (Focal lengths longer than 2,600 mm will not show the entire solar disk.) You can boost the effective focal length of lenses with a 2x or 3x teleconverter. For any particular focal length, the diameter of the Sun's image is roughly equal to focal length divided by 110.
Veteran eclipse photographers often test their equipment on the Moon around the time it's full. Not only is the Moon's apparent size about the same as the Sun's, but it has roughly the same total brightness as the corona. A series of exposures, made along with careful notes, can reveal potential problems with focus and vibration, as well as internal reflections and vignetting in the lens.
If you plan to photograph the eclipse's partial phases, make sure you have a visually safe solar filter securely mounted on the front of the telephoto lens or telescope objective. Polarizing or photographic neutral-density filters are not safe for visual use. Be sure to test your setup on the midday Sun well ahead of the eclipse to determine the best exposure to use.