Re: Astrophotography Stars w/ Digicam SLR

In article <589pn416a557kig9t5319824qdsdgeai0f@xxxxxxx>,
William Hamblen <william.hamblen@xxxxxxxxxxxxx> wrote:
On Sun, 25 Jan 2009 08:13:41 -0800 (PST), Billy <UseNewz@xxxxxxxxxxx>
wrote:

I recently began taking images of stars from my Nikon D300 digial SLR
and I'm amazed - when I take the picture I can many more stars in the
image than I can with the naked eye. Does anyone know why this would
happen, could the image sensor be stronger than my eyesight?????

Your camera can take time exposures. Your eyes can't. Your naked eye
has a maximum exposure of about 1/10th of a second. Your camera can
take as long an exposure as you want. Your eye has about a 5 mm
aperture. Your camera has a bigger aperture depending on the lens.
More aperture means more light. More light for a longer exposure
means fainter stars.

I think this is the right point to show off
http://fivemack.livejournal.com/178881.html and
http://fivemack.livejournal.com/179278.html. Panoramas of the whole
sky, on a half-decent night from a dreadful location in central
Cambridge. Through thick sodium glare in which you can scarcely pick
out gamma UMi with the naked eye, 20 seconds at ISO1000 12mm f/4 gets
stars down to about magnitude seven.

Tom
.

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