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|| SportsShooter.com: News Item: Posted 2004-01-29

Shoot the Moon
'It's a marvelous night for a moon dance ... ' --- Van Morrison

By Tom Dahlin

Photo by Tom Dahlin

Photo by Tom Dahlin
How many times have you been on assignment, lugging your 400mm or 600mm lens, and a spectator says "Hey ... I bet you can see the craters on the moon with that thing"? Well, the correct response is "damn straight, want to see some examples? ...

On the evening of October 27-28, 2004, a total lunar eclipse will occur, visible within the US. According to Sky and Telescope Magazine (see references), the Moon will enter the Earth's umbra shadow at 9:14 PM eastern time. The shadow will cover the moon in totality from 10:23 to 11:45 p.m. The Moon will depart from the Earth's umbra shadow at 12:54 a.m. This makes for an excellent opportunity to make some cool images. This note describes a technique for capturing this event using that big glass you own.

Overview
Using a long telephoto lens to shoot the moon is nothing new. You've probably done this several times. Take your 600mm, add on a 1.4 or 2X converter, and you can almost fill the frame with the full moon. An example of this is shown in figure 2. The problem is, this is a pretty boring shot by itself. If you use this long glass to shoot the eclipse, you'll find that no one single image of the moon is particularly interesting by itself. To the casual observer, a shot of a partially eclipsed moon looks very close to a regular shot of a half, quarter, or whatever moon. Even when fully eclipsed, a full frame shot of the moon looks pretty ordinary, only differing in the orange color it often takes on.

There are a couple of ways to make the shot more interesting. Both involve adding a temporal aspect to the shot through multiple exposures or compositing images. As multiple exposures are not possible with my digital cameras, I've adopted a composite method to produce the same effect. The result is labeled a 'photo-illustration' to keep everybody happy.

Photo by Tom Dahlin

Photo by Tom Dahlin

Figure 2.
One method is to record multiple images of the moon rising over an interesting foreground and making a composite of them. Suitable foregrounds for sports shooters might be the local dome or stadium. To get the foreground in the frame, you'll probably need a normal to medium telephoto lens and careful planning on when and where the moon will rise and eclipse (see resources at end of note for how to get this info). Because of the need to use a shorter focal length lens, the moon itself will occupy but a fraction of the image frame.

Another method involves shooting multiple; separate single frames of the moon with a long telephoto and compositing them together. The advantages here are that the moon is recorded with breathtaking detail (you really can see the craters) and you have much more flexibility in your timing and positioning. As the whole point of this note is how to use your big glass to shoot the moon, this is the method I'll describe.

Tips for Shooting
The actual shooting is easy. Do a little homework and find out where the moon will be moving (approximately) during the eclipse. You can look this up on the web, or simply observe where it is on the preceding evening. Find a place to set up that provides an unobstructed view and is comfortable. Bring a lawn chair and some refreshments and you are set to go.

You should plan on shooting a set of bracketed exposures at regular time intervals. If you shoot on 15-minute intervals, it makes it easy to select a subset showing an equally spaced continuum for the composite.

Getting a correct exposure for a full moon is not terribly difficult. The sunny sixteen rule works pretty well for an uneclipsed full moon. However, things get trickier as the earth's shadow falls across the moon. It gets really dicey at the moment of totality when the moon has faded to a soft orange ball. In the old days, one relied on printed exposure tables such as the one in Arnold's Astrophotography book (see resources). With digital cameras, it's become quite a bit easier.

All you really need to do is take an educated guess, shoot, look at your histogram and re - shoot if needed. Using ISO 400, I started at 1/500 at f/11 for the un-eclipsed moon and took a test shot. I looked at the histogram and opened up my f-stop until I just started seeing blinkie highlights and then closed down a stop. I followed this method as the moon went through the eclipse phases. At totality, it gets really dim and you'll probably find your exposures are will need to be around _ to 1/2 second at f/8 at ISO 800-1250. Note that I cranked up the ISO to prevent camera shake from degrading the image.

On the subject of camera shake, it really helps to have a remote cable release and a sturdy tripod/sandbags. I used a pocket wizard pair as my remote release so I didn't have to touch the camera to trip the shutter. Overkill? Maybe. Convenient? Definitely.

Although not as fast as most action you are accustomed to, the moon does move pretty rapidly when viewed through a long telephoto. Figure 3 shows a composite series of exposures taken 30 seconds apart without moving the lens. Because you'll need to keep adjusting your lens to track the moon as it travels, it helps to have a gimbaled lens mount such as a Wimberly or Kirk Cobra.

Photo by Tom Dahlin

Photo by Tom Dahlin

Figure 3.
Another problem is focusing. You'd think that this would be a non-issue. A nice big bright target against a dark sky. Well, it is, until the moment of totality, i.e., your money shot. It this point, the moon is no longer very bright at all. In fact, it is pretty dim. So dim that it is nearly impossible to accurately focus on it. So.... you need to manually pre-focus while you can and tape down that focus ring.

Don't do what I did last May and try and refocus each image just prior to exposure. You'll be really cranky at the 'peak action' moment. I was able to save myself here by bracketing my focus until the moon got bright enough to again accurately refocus.

Nuts and Bolts of the Composite
Making the composite is pretty straightforward. To make an illustration such as in the opening image of this note, choose seven equally spaced (in time) frames. Make a black canvas in Photoshop that is approximately seven times as wide as one on the moon images. Copy and paste each of the seven moons onto the canvas.

Each time you paste, a new layer is created and you can move and position the element exactly where you want it. For each layer, make a mask of the moon by lassoing it, and under the layer menu, select 'Add Layer Mask … Reveal Selection'. This masks everything but the moon on that layer and prevents the dark sky of one image from overlapping the moon image on other layers. That's all there is to it. After you've got all this done, you can go in and fine tweak placement before final cropping and collapsing the image to single layer.

Wrap Up
Well, that's about it. While lunar eclipses are not as rare as solar eclipses, they are much easier and safer to photograph. And you can't go blind from shooting them. Even if you chimp. If you've got the big glass and not much to do on the night of October 27th, give this a shot. It's a great way to spend a few hours. Last May, I set up in a local neighborhood park and let all the kids come and take a look through the lens. The only thing I forgot was a cooler with some refreshments for the adults.

References
Celestial Highlights for 2004, Paul Dean, Sky Watch '04 Annual Guide to the Night Sky, Sky and Telescope Magazine, page 38.

Resources
Moonrise tables showing time, azimuth and elevation for any US location can be generated and printed from the web page hosted by the U.S. Naval Observatory Astronomical Applications Department at: http://aa.usno.navy.mil/.

Another favorite astro web site of mine is: http://www.spaceweather.com/.

One of the giants in astrophotography is Fred Espenak, aka Mr. Eclipse. Fred has probably the most comprehensive website on eclipses. His homepage is http://www.mreclipse.com. Check out his lunar eclipse primer and stunning eclipse photography.

A couple of great books on astronomy and astrophotography are:

Astrophotography: An Introduction, by H.J.P. Arnold, published in 1995 by Sky and Telescope's Sky Press.

Nightwatch: A Practical Guide to Viewing the Universe, by Terence Dickerson, published in 1998 by Firefly Books.


(Tom Dahlin is a freelance photographer based in Minneapolis, Minnesota. An engineer by training, he spent the last 10 years of his career in 3M's corporate research department before embarking on his freelance career. This partially explains his need to overanalyze and document seemingly trivial events. Check out his SportsShooter.com member page or contact him at: tdahlin@isd.net.)


Related Links:
Tom Dahlin's member page

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