RE: [APML] Film Choice for Total Lunar Eclipse (warning! OT)

["Dan Kaestner" <warriordan@comcast.net>]

Wade,

Thank you for the help.
If the E200 is going to make it that critical I have to ask what you'd
recommend for film
for this event that may give good results?
I'd piggyback on my scope but as I said I'm real new to this and it takes me
forever to polar align.
And the fact that the eclipse will be starting (or in progress) at Moonrise!
(west coast)
Probably be over by the time I got aligned ....LOL

Thanks again
Dan

-----Original Message-----
From: astro-photo-bounces@seds.org [mailto:astro-photo-bounces@seds.org]On
Behalf Of Thomas W. Earle
Sent: Monday, October 25, 2004 8:40 PM
To: 'Discussion of Film Astrophotography'
Subject: RE: [APML] Film Choice for Total Lunar Eclipse (warning! OT)

Dan,

Assuming F/5.6 and a focal length of 200 mm, you have about 2-4
seconds of drift to work with before the Moon is blurred too much by
the movement of the Earth and the Moon together.  For critical work
(i.e. no blurring), you only have about 1 second.  Your E200 is
really going to limit you, especially if it turns out to be a darker
eclipse.  For example, Michael Covington recommends an exposure of 5
seconds at ASA 200 if the eclipse is "light"; however, the exposure
becomes 1-2 minutes if the eclipse is dark.  It will probably end up
somewhere between these two values.  First, I would recommend
pushing E200 two stops which will give you an effective ASA 640.
Pushing the film will give you a much wider "anti-blurring" window.
Assuming you push E200 2-stops, you should bracket your exposures
between 1/4 and 8 seconds.  Keep in mind, the moon is going to blur
quite a bit during the 8 second exposure and my give unacceptable
results, but it's still worth a try, especially if it is a darker
eclipse.  Also keep in mind, the recommended exposure for a dark
eclipse is 20 seconds.  At this exposure, the moon would be a thick
reddish-orange blob.  Exposures on either side of totality will vary
depending on if you are exposing for the bright portions or dark
portions.  For the lighter portions, start with 1/500s.  For the
darker portions, try 1/2s.  Remember to always bracket a stop on
either side of these values.  For example, 1/4s, 1/2s, and 1s.  The
hope is that one of these exposures will be right.

If you have a 1-degree spot meter, as a starting point, you can
center the moon and take a reading.  You should then decrease the
light hitting the film by 2 stops or 4x.  For example, if the light
meter gives a reading of 1/30 at f16, you can either expose for 1/30
at f32 or 1/125 at f16.  Keep in mind, the moon is about a 1/2
degree so the meter is going to average its light over a 1 degree
area (i.e. overexpose the moon); hence, the need to decrease the
light.  Finally, the 2 stop is only good for a fully lit moon (i.e.
either full or during totality).  If the moon is a quarter lit, you
will need to decrease the light hitting the film by 4 stops or 16x.

I hope this helps and good luck.

Wade


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