In photographing the moon, when low on the horizon, how long a shutter speed can be used before the motion of the moon becomes evident. Also I am uncertain about exposure; I believe one should calculate the value as if exposing for the sun but I am a bit uncertain. Has anyone had any experience using graduated neutral density filters for moonscapes? I will be shooting over the ocean just at, and a bit after, moonrise.

Thanks for the help.

DAB

-- Douglas A. Benson (dab@evcom.net), November 12, 2000

Answers

1/8th at f/16 with 100ISO film. But it depends on your geographical latitude, and how much detail you want in the moon's surface to a certain extent.
The moon's surface has the same illumination as the surface of the earth in daylight, so with the moon overhead in a clear sky, 125th at f/8 with 100 ISO gets you a perfect exposure, craters and all.
A little overexposure gives a more artistic than accurate rendering, an allowance of one extra stop for the extra atmospheric absorbtion close to the horizon, and no longer than 1/8th of a second, was how I arrived at the above exposure.

-- Pete Andrews (p.l.andrews@bham.ac.uk), November 13, 2000.

I have used 1/ISO @f8 - f11 with good results.

The moon travels about 15 degrees per hour, actually we are moving with it as well so it's not just the moon that's moving. Anyway, the moon moves it's own diameter about every two minutes. Shutter speeds much slower than 1/4 of a second may start to blur and lose detail. Multi-second time exposures blur all detail and if they are quite long you will get an elongated trail.

The full moon usually rises within a few minutes of sunset and this varies throughout the year. Usually, the best photo opportunities for the full moon are the evening before the "official" full moon as it rises earlier while there is still some ambient daylight for the landscape.

Following two links courtesy of the U.S. Naval Observatory help you compute moonrise data for your location. Azimuth bearings are especially helpful, as these vary month to month.

http://riemann.usno.navy.mil/AA/data/docs/RS_OneDay.html

http://aa.usno.navy.mil/AA/data/docs/WebMICA_2.html

-- C.W. Dean (cwdean@erols.com), November 13, 2000.

I've always used 1/ISO of the film @ f16. This is, of course, the "sunny 16" rule. Answer a question. What is lighting the moon? And the answer is direct sunlight. Those of you who "zone" may want to put your own interpretation on the sunny 16 rule, but it works for us mortals.

-- David Grandy (dgrandy@accesscable.net), November 13, 2000.

Ansel Adams always suggested that 1/8, or faster, was required to get a sharp shot of the moon.

-- Ed Farmer (photography2k@hotmail.com), November 13, 2000.

Also keep in mind that we tend to overesitmate the size of the moon. It's a great deal smaller than most people realize, only 1/2 degree across (same as the sun). This means that if a lens covers 40 degrees, EIGHTY full moons would fit across the frame! Your little finger at arms length is TWICE the width of the full moon. My Meade ETX is about 1200mm, and even at this focal length the moon does not fill a 35mm frame.

Having said all this, it's reasonable to ask why the rising full moon looks as big as a dinner plate. It's an illusion, of course, and I'm not sure that thre's any generally accepted theory about why we percieve it the way we do. Actually, the full moon is slightly smaller when it's on the horizon than when it's overhead!

And yes, the moon is lit by the sun, so the sunny f16 rule applies. An extra stop or two won't hurt, though, because the moon is actually very dark. Don't quote me on this, but I think its darker than a standard gray card. I seem to recall reading that the lunar surface is darker than asphalt in some places.

Okay, astronomy lesson over! Go shoot the moon!

clear skies - Kevin

-- Kevin Bourque (skygzr@aol.com), November 13, 2000.

Many thanks to everyone for the very helpful responses. Hopefully, I will now be able to make some good images while feeding the mosquitoes.

DAB.

-- Douglas A. Benson (dab@evcom.net), November 14, 2000.