Photograhping the comet

["Richard W. Hemingway" <n5xrd@telepath.com>]

I guess I need to make up for my "flashing the comet" crack.  Several weeks
ago I mentioned the Sky and Telescope and comet webb pages, along with the
results I got with ASA 400 Kodak Royal print film.

Since most of us will be doing this on a fixed tripod, several matters are
to be considered.

        (1) choice of film.  This depends on how dark your site is.  A
balance must be made between the speed of the film and the light pollution
of the site.  Probably, to start with the choice will be between ASA 400 and
800.  If the site is bright, too fast a film will wash out the comet, due to
light pollution.  I found that ASA 400 was about right here in Norman, OK
which picks up the lights from Oklahoma City (it is the main reason I sold
my 14" Celestron and closed the observatory in my back yard).  If you go out
into the country, ASA 800 or 1600 may work well.

        (2) lens to use.  Since we are looking at an extended object, both
from a photographic and physical standpoint, most of us will use focal
lengths from 50 to 200mm. I found my 75/1.4 was very good, wish I had used
the 135/4.0.  Without guiding it will not be possible to get good pictures
of the comet head, although you might try it.  The shorter focal lengths
will show the long tail from a dark site.

        (3) exposure time.  Use the widest opening you have.  I used 1.4 on
both the 35 and 75 lens.  Don't worry if it is not the best opening.  I
found that 20-40 seconds at 1.4 were very good.  BTW there will be star
movement with the longer focus lengths.  This does not matter with the comet
as it is fuzzy anyway and won't show much. Too keep the stars looking more
or less round, you can use the formula that shows the movement for one
second of exposure for focal length:  0.00007 x FL (in inches).  As you
probably can go up to .0035 " of movement before it is objectionable, divide
the answer obtained into 0.0035.  This equals: 35mm - 36s, 50mm - 26s, 75mm
- - 17s, 135mm - 9s.

This is no real problem with the comet.  I have seen 10 min. exposures of
135mm lens with the stars trailing in the background and they weren't
objectionable.  I have a 10 minute exposure with my 135 at f4.0 in my camera
but won't get it developed for a while.

Along with the webb sites Fred posted, look at some of the last issues of
Astronomy and Sky and Telescope.  There are also several good book on
astrophotography.

        (5) With either a Leica rangefinder or SLR (or other camera) don't
rely on the shutter to not vibrate the camera, even with mirror lockup.
Hold a card or hat in front of the lens and open with a locking shutter
cable.  Then remove the hat or card and time the exposure. (BTW the best
cameras I found for photographing through a telescope were a rangefinder
Leica with the viso, or mechanical SLR with mirror lock up - I used the
Nikon F, and later the F3.  If you take long time exposures in the cold the
batteries will give out if no mechanical release is available)

        (4) Get a big flash (I mean big!!!).

Good hunting

Dick Hemingway
Norman, OK