Shooting the Moon and the Stars

[Jay Gould]

During our trip to South America, one of the big deal “things” is to be at Iguacu Falls during the full moon. Fortunately, we are going to be there 28 Jan – 1 Feb 2010, which is the full moon period.

Can you give me some suggestions, point me in the right direction regarding tutorials, pertaining to nighttime photography in general, and moon photography in specific?

[Roger Clark]

Jay,
I can give a few pointers.

Remember the moon is lit by the sun. Lunar rocks and soils as slightly darker than typical Earth rocks and soils, so instead of using the sunny 16 rule for terrestrial scenes (1/ISO = 1/seconds at f/16, so at ISO 100, 1//100 second at f/16) use the sunny f/11 rule: 1/ISO at f/11, except the night of full moon, when it is back to sunny f/16.

This makes it hard to do twilight scenes with the moon: the moon is usually much brighter, so HDR might be the way to go.

Stars are very faint so you need long exposures. But then the Earth rotates which elongates the stars. If you want the stars to be round, you'll need to use shorter exposures, or use a tracking device. To compute the exposure time before stars trail, use the following. The Earth rotates ate a rate of 15 arc-seconds per second.

One pixel on your camera is: 206265 * (pixel_size_in_microns / 1000.) / lens focal length = pixel sixz in arc-seconds.

Example: Canon 5D Mark II has 6.4 micron pixels. If you use a 50 mm lens, each pixel sees:
206265 * 6.4 /1000 / 50 = 26.4 arc-seconds.
At 15 arc-seconds per second, the start drifts one pixel (at the celestial equator) 26.4/15 = 1.76 seconds.

In practice, due to the blur filter, you can go a couple times longer, so 4 seconds and still have pretty round stars. By 10 seconds they will appear as elongated ellipses. (the constant 206265 is the number of arc-seconds in one radian.)

For star trails, go much longer. See Roman's excellent primer:
DIGITAL STARS TRAILS PRIMER
http://www.birdphotographers.net/for...ead.php?t=5683