Tips for Photographing a Lunar Eclipse

It's been almost three years since the last total lunar eclipse was visible in North America and the next total eclipse visible for the entire continent won't come until April 14-15, 2014 (the West Coast will only see part of the one that occurs in 2011). If you want to try photographing one don't miss out on the opportunity this Monday night/Tuesday morning! This one is especially exciting because it coincides with the solstice. Sad thing for me in Southern California is that right now the forecast is for heavy rain.

Assuming you don't do any astrophotography and don't have the ability to use a telescope, tracking equipment and don't want to be bothered with calculating things like azimuth and altitude, here are a few tips for photographing an eclipse that I used to make the above composite of the total eclipse in August 2007:

First the basics: I do hope you realize that it can get cold when you stand outside for hours in the middle of the night in winter and don't need to be warned to dress warmly. I always have to laugh when I see that tip. You should take a flashlight, preferably a red astronomer's flashlight that won't ruin your night vision, so you can easily see your camera controls. I have a headlamp with a red light that is perfect because it leaves both my hands free. A thermos of hot coffee or your favorite warm beverage isn't a bad idea either!

These tips are good for both film and digital photography, each has its own considerations. With film you need to be concerned about reciprocity failure at long exposure times; with digital you need to be concerned about noise levels at higher ISOs.

Lens
You really have two choices - go with a wide angle and plan to capture a series of photos showing the moon moving across the sky, or go with your biggest telephoto and capture a series of single moon images that you later arrange in editing software any way you want.

If you choose to go wide angle you will need to account for the location of the moon in the sky at the onset and conclusion of the eclipse. An rough way to do this without needing to calculate altitude and azimuth is to scout your location the night before, assuming you are up to spending back-to-back all nighters outdoors or are willing to set your alarm throughout the night. The moon will appear very small in a wide angle frame so it's best to find an interesting foreground to add interest and provide context.

The latter option is the easiest if you don't understand how (or want) to plot the course of the moon and plan for it in your final image but you need a long lens. It also gives you the option to arrange your sequence of images creatively later in editing software. 200mm is a bare minimum, 500mm even better. You can use a teleconverter but you need to account for it in your exposure calculations since a teleconverter cuts down on the amount of light entering your camera. A 2x converter means you'll lose two stops of light. The above images were shot with a 70-200mm lens with a 1.4x converter and a Canon APS-C sensor, yielding an effective focal length of 448mm and the images of the moon were still fairly small.

The size of the moon's image can be calculated using the formula:

Focal Length(mm)/109

So a 50mm lens yields a 0.5mm image of the moon, a 200mm lens yields a 1.8mm moon and a 500mm lens yields a 4.6mm image.


Exposure
You need to expose manually otherwise your camera's exposure meter will probably be tricked by the amount of dark sky in the frame and overexpose your images, leaving you with a bright white circle for the moon. The Sunny 16 rules applies to the full moon, which simply means that the correct exposure for a sunlit object at f/16 is 1/ISO. If you are shooting at ISO400 a good starting exposure for a sunlit object is f/16 at 1/400. You won't see much of a difference in exposure when the moon is in the penumbra, but when you can see the visible shadow line of the umbra on the moon's surface that's when things get fun. As the moon gets darker you will need to increase your exposure accordingly and bracket, bracket, bracket. During totality the moon will be completely in the earth's shadow (the umbra) and you will need a long exposure. It's best to factor this into your early planning; use a tripod and shutter release throughout your shoot and choose an ISO high enough to keep your shutter speed below two seconds at totality to prevent blurring if you don't have tracking equipment (remember, the moon is constantly moving!) but not so high that noise becomes an issue. ISO 400 or 800 is usually good, higher depending on how your camera handles noise. I used ISO400 and my image at totality was shot at f/5.6 for 1.3 seconds.

Here are some good starting exposures (but don't forget to bracket, bracket, bracket!):

ISO 400
Full moon - f/16, 1/500
Moon in penumbra, shadow line of umbra visible - f/8, 1/125
Totality - f/2.8, one second

I hate coding tables :P and I won't copy work that someone else has already put together, so I will point you to an outstanding exposure guide put together by Fred Espanek - Mr Eclipse. It takes into account the magnitude and the Danjon value (brightness) of the eclipse.

L = 0     Very dark eclipse.
               Moon almost invisible, especially at mid-totality.
L = 1     Dark Eclipse, gray or brownish in coloration.
               Details distinguishable only with difficulty.
L = 2     Deep red or rust-colored eclipse.
               Very dark central shadow, while outer edge of umbra
               is relatively bright.
L = 3     Brick-red eclipse.
               Umbral shadow usually has a bright or yellow rim.
L = 4     Very bright copper-red or orange eclipse.
               Umbral shadow has a bluish, very bright rim.


Click here to learn more about the Danjon scale on NASA's website.

Since these are just recommended exposures and based on your judgement of the L value, at totality you will want to bracket as much as 2-3 stops over and under the recommended exposure.

The entire eclipse will last approximately 4.5 hours. You can see the timing of the various stages in your time zone on the chart at Sky & Telescope here.
You'll probably want to take bracketed exposures every 10-15 minutes or so throughout the eclipse so make sure you have a big enough card (or enough cards). Just as a guide, I took 283 shots when I shot the one in 2007. Nothing would be worse than running out of data storage before the eclipse is over after spending several hours out in the cold!

We don't often have a chance to view or photograph a total lunar eclipse, so here's hoping for clear skies and if you are one of the lucky ones who can spend the night outdoors Monday please feel free to post links of your images here.