ems@amdahl.UUCP (ems) (01/22/86)
There has been a discussion on net.space about the best way
to photograph the comet and have a picture of the kids in the
same frame (hopefully without resorting to darkroom magic.)
Some have suggested a time exposure of the comet and a flash
of the kids. Various lens/time combinations were recomended.
Here is what I could glean from a couple of magazines: (reprinted
without permission. I *do* hope they think of this as advertizing... :-)
Photo Information Almanac '86: (chart of Lunar Eclipse exposures)
Tentative Exposures for Lunar Eclipse Photography
ASA
Stage of Eclipse 25 32 64 125 160 400
full moon, Time (sec.) 1/250 1/250 1/250 1/250 1/250 1/250
clear sky Lens opening f/5.6 f/5.6 f/8 f/11 f/12 f/22
Moon deep in Penumbra Time 1/60 1/60 1/60 1/60 1/60 1/60
up to First contact and Lens f/4.5 f/5.6 f/8 f/11 f/12 f/22
after Fourth contact
At Second and Third Time 3 sec 2 sec 1 sec 1 sec 1 sec 1/2
contacts Lens f/2 f/2 f/2 f/3.5 f/4 f/5.6
MID Totality Time 12sec 8 sec 4 sec 4 sec 4 sec 2 sec
Lens f/2 f/2 f/2 f/3.5 f/4 f/5.6
Note 1. When the moon is partially in the umbra, exposure must be
selected for the umbra portion or the penumbra portion. No
film can accomdate both at one time.
(It is my beliefe that the f/12 given in the first to cases for asa 160
should be f/16; but what do I know...)
From Photo Graphic October 1985, article titled Shooting Stars:
Film: Slides are probably the most rewarding medium (...) Start with
a fast color slide film, such as Fuji 1600D, Kodak P800/1600, 3m 1000,
or Agfachrom 1000RS. If you are in a large, light-poluted city, however,
experiment with a fast black-and-white film (like Kodak Tri-x, Ilford HP5,
or Agfapan Vario-XL Professional) combined with a red filter to block
some of the city lights
Whatever you are using, try pushing it. (...) At this point you are
looking for the combination that will reveal the most stars before being
smothered in grain and fog. Later, when you are become more proficient
with long exposures, try some of the slower slide films for better
resolution.
Lenses: A lens's ability to record faint point sources - the
stars themselves - depends, not on the f-number, but on the
absolute size of the aperture. An f/16 lens with a 10-inch
aperature will record fainter stars than an f/4 lens with a 6-inch
aperture. This probably sounds odd to anyone accustomed to
terrestrial photography, and when we get into 'extended
sources' - anything, like the moon, that is of sufficient size to
be resolved by the lens - we are back on familiar ground (...)
This is because for a given aperature, images of extended objects
expand, and therefore become dimmer, as focal lengths and f-numbers
increase, whereas point sources do not. (...)
As a novice astrophotographer, your first lens should be the
50mm that came with your camera, provided it has a reasonably large
aperture. An f/2 is good, but f/1.2 is better. (...) The wide
field is essential if you want early pictures of Halley's
Comet and you only know that it will be somewhere in the constellation
Taurus.
(...) Using the lens is simple: open the aperture all the way
and focus on infinity.
Exposure: On a dark night, mount your camera on a tripod and point
it at the sky. Take a series of test exposures, for 5, 10, 15, 20,
30, and 60 seconds. Be sure to keep good records. Each roll should
begin with at least two well lit frames to let the lab technician
know where the frame lines fall. Enclose a note with the exposed
film explaining that the roll contains star pictures. Otherwise the
lab might conclude that they are botched exposures and cut them up.
You will find that with each longer exposure more stars will
appear until, around 15 or 20 seconds, the stars will begin to
record as short streaks rather than sharp dots. (...) With a
fast film, this 15 to 20 second limit should permit you to
record stars as faint as magnitude seven, one magenetude beyond
the reach of the unaided eye.
(...)
__________________________________________________
Well, what does this all mean about photos of The Comet?
Looks like fast film, fast lens, under 10 second exposure
and flash the kids. You may want to refocus and reset the
aperture for the flash ...
Hope this helps.
--
E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems
This is the obligatory disclaimer of everything.