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I used an Olympus 3030 digital camera. It has a complete manual mode, which
is what I used. Even though it is a digital camera, it has settings for
approximate ISO of 100, 200, 400. My understanding is this setting on a
digital camera alters the operating parameters of the CCD such that the 400
setting requires four times less light (than the 100 setting), but a
penalty of hot pixels (noise) and some loss of latitude.
Prior to April 25, I had verified that I got better star pictures at ISO 100
and longer exposures rather than ISO 400 and shorter exposures. You might
want to experiment with a particular brand of digital camera to make sure
this is true for thar camera.
Therefore, I set the camera on ISO 100, manual focus set to infinity,
aperture wide open at f/2.8, and tried exposures of 2, 4, 8, 12, and 16
seconds. (16 seconds is maximum with my camera). I could see right away
using the LCD screen that 2 and 4 seconds were too short, but it was
difficult to tell whether 8, 12, or 16 was best. I took a couple exposures
at each setting. The ability to adjust brightness, contrast, and gamma at
the computer made these almost equivalent in the end.
I used a tripod, of course. This camera has an infrared remote control that
I usually use to trip the exposure so I don't shake the tripod during
shutter release. On April 25 I forgot to take the remote control, so I used
the 10 second time delay shutter release (self-timer) to release the
shutter.
I didn't write down the exposures, and might not have known the exposure for
the actual picture placed on my web space, except for one interesting
thing... a bit below and to the right of Jupiter (about 4 o'clock) an
airplane flew across the sky during this exposure. The strobe light on the
plane blinks about once a second. It left a trail of about 12 dots across
the picture so this was probably a 12 second exposure, but could have been
16. To see the plane you have to have the brightness, contrast, gamma set
correctly when you view or print the picture.
Before getting a digital camera I also took sky pictures with traditional 35
mm film. I used ISO of 100 or 200 (sometimes 400) and a camera with a f/1.4
lens. I used exposure times of several seconds. My 35 mm camera is old and
has a bulb setting. Sometimes I closed the lens some and took real ling
exposures so the stars would streak.
With modern cameras that have maximum times of 2 or 4 seconds I would think
you could do pictures with ISO 400 and lens openings of
f/2 or f/2.8. The
only way to know is to experiment.
Michael Edmiston
Bluffton College
edmistonm@bluffton.edu