Whether observing or photographing, most people start with the Moon. As the sky’s brightest target, the Moon holds up with simple techniques, including holding a smartphone to a telescope eyepiece. As you get more comfortable with the technique, imaging a lunar eclipse is a good time to practice astrophotography while catching some unique views.
For eclipses, I use an Android Samsung Galaxy S9 smartphone clamped to my telescope with an Orion Steady Pix adapter and a Vastar phone clamp. In manual (pro) mode, this setup allows me to control the ISO and shutter settings from 10 seconds in night mode to a fast 1/24,000th of a second. The recent line of Galaxy S11 smartphones offers a 48-megapixel camera, which greatly improves the resolution.
While we use an Android smartphone, which has the versatile ability to adjust camera settings in pro mode, when it comes to shooting the Moon any smartphone will likely work, as long as it has a manual/pro setting to control exposure and ISO settings. The phone clamp is also key for fine positioning of the phone camera at the telescope’s focus. Unlike cheap selfie clamps, the Vastar clamp has a wide, thick adjustable bracket, capable of holding the phone securely in place.
For piggyback shots, we use a Nikon D3200 DSLR camera with a Tamron 18-200mm zoom lens. Their advantages for astrophotography include light weight and affordability, but they are admittedly older versions and can be replaced with more up-to-date gear. Tamron is compatible with Nikon gear, and the wide range of the zoom covers what would otherwise call for several fixed lenses. Good equivalents on the current 2021 photography market are Nikon’s D3500 (MSRP $599.95) with a 24.2-megapixel sensor, and Tamron’s recently released 18-400mm DI-II VC HLC lens. (MSRP $599.99)
Lunar eclipses, which occur when the Moon passes into the shadow of the Earth, come in three basic flavors. In order of noteworthiness from ‘meh’ to ‘wow!’, they are: penumbral, when the Moon passes through the bright outer penumbral shadow of the Earth; partial, when the Moon grazes the inner dark umbral shadow, and total, when the Moon is fully immersed in the dark umbral core of the Earth’s shadow.
Unlike quick total solar eclipses, total lunar eclipses are slow, stately affairs; the Earth’s shadow is 2.5 times the apparent size of the Moon at the same distance, and the longest totality for the current millennium just occurred during the July 27, 2018 eclipse, at 102 minutes 57 seconds in duration.
The lengthy eclipse period means that exposure settings for lunar eclipses are straightforward right up until totality when the Moon can dim precipitously. (Incidentally, the brightness of the Moon is described by what’s known as the Danjon Number, with 0 as the darkest, and 4 as the brightest.)
You’ll need a telephoto lens with a focal length of at least 200mm to yield a Moon 1.8mm across on the image sensor. A 400mm lens will yield a Moon image 3.7mm across. ISO 200-400 with a shutter speed of 1/100 to 1/1000 is ideal up to about 50 percent partial phases, at which point you’ll want to start dialing down to 1” to 4” exposures as totality approaches. Tracking will be needed during slower shots; Piggybacking the DSLR camera on a larger telescope that tracks works great.
If you’re lucky enough to see the eclipse near moonrise or moonset, you can potentially catch the eclipsed Moon along with foreground objects such as buildings, hills, statues, etc. Because the Moon is so tiny in the sky, you’ll need a distant of from 500-meters (a third of a mile) to a kilometer (0.6 miles) from the camera to the foreground object to yield a statue-sized Moon image. Apps such as PhotoPills, the Photographer’s Ephemeris and Vito Technology’s Ephemeris can help you plan out the shot beforehand to get positioned. These apps will overlay the sunrise/sunset and moonrise/moonset positions for your location (from GPS) onto Google Maps to help you find the best site to capture foreground objects on the horizon. If possible, scout this out the night before, when the Moon is pretty close to full.
Advanced photographers will want to consider long exposures and mosaic shots taken from the partial phase to total and back to partial, to reveal the curved nature of the Earth’s shadow or show the Moon’s color changes during the eclipse. And be sure to watch for the unexpected. For example, a report of a flash witnessed on the Moon during the January 21, 2019 total lunar eclipse sent many imagers scrambling to review video and images to see if they had captured the rare phenomenon.
For more on imaging lunar eclipses see Fred Espenak’s Mr. Eclipse website.