On 10/10/2014 6:34 AM, bj@xxxxxxxxxxxxxx wrote:
Chuck wrote
There are two more total eclipses coming up next year in April and
September so maybe you'll get another couple of chances. Until then you
can practice on the non-eclipsed moon which should be a bit easier.
The problem with this plan is that exposure must be much longer when the
moon is in the umbra. There's actually a scale for how dark any
particular eclipse will is. <http://en.wikipedia.org/wiki/Danjon_scale>
Practicing on the full moon will give a false idea of exposure, by many
stops.
This last one was not particularly dark: "Helio C. Vital leads a group
of Brazilian amateurs who've carefully measured the brightness of many
past lunar eclipses. Taking into account the current aerosol content of
Earth's atmosphere, he predicts the October 8th event will be fairly
bright, the Moon at mideclipse being roughly as lustrous as Jupiter
(magnitude –2 to –3)."
Unfortunately: "When the last of the moon enters the umbra, the total
lunar eclipse begins. How the moon will appear during totality is not
known. Some eclipses are such a dark gray-black that the moon nearly
vanishes from view. At other eclipses, it can glow a bright orange. The
reason the moon can be seen at all when it's totally eclipsed is that
sunlight is scattered and refracted around the edge of the Earth by our
atmosphere. To an astronaut standing on the moon during totality, the
sun would be hidden behind a dark Earth outlined by a brilliant red ring
consisting of all the world's sunrises and sunsets."
So one can't know ahead of time what the exposure will be.
The exposure guide half way down this page shows how great the
difference may be. <http://www.mreclipse.com/LEphoto/LEphoto.html>
It suggests that for f5.6, ISO 200, if full moon exposure is 1/2000*,
the brightest total eclipse would be 1 sec., while a darker eclipse
could go out in to minutes. If you look at his multiple exposure image
above, you'll see that the guide seems to be pretty accurate.
So, at least 11 stops darker! That means a lot of light must be gained
using aperture, and ISO to retain a shutter speed that won't blur
noticeably, say 1/2 sec. Basically, it can't be done for any but a
bright eclipse using my 1000/11 lens without astronomical ISO or a
tracking mount.
Soooooooo ... Shooting a full moon really doesn't prepare one for an
eclipsed moon. Some combination of ND filters and polarizers might allow
checking out one's equipment and technique?
Darkly Loony Moose
* I know, Loony 11 suggests f/11 @ 1/200, or f/5.6 @ 1/800. My own best
shots were f/11, ISO 200, 1/60. Pretty close to Loony 11. As he says,
use his table as a starting point.