Re: A beginner question

On Sat, 09 Jun 2007 12:56:18 -0700, "actuary@xxxxxxxxx"
<actuary@xxxxxxxxx> wrote:

I reently purchased a Canon PowerShot SD1000 for strictly home use. I
was out the other night trying to locate Vesta and I did but then I
wondered if I could capture Vesta (magnitude 5.8) on a 2 second
exposure (maximum exposure time) using the Canon 1000SD camera.

I don't have a tripod so I didn't try. What is the applicable
mathematics to answer the question?

I assume you mean using just the lens in the camera? Then yes, it might
just barely be possible. You need to consider the number of photons
received. In the case of a mag 5.8 object, and your ~3mm aperture,
that's about 1000 photons per second. Between atmospheric losses, and
issues of camera sensitivity, you might actually record about 25% of
these, or 250 photons (500 in 2 seconds). That would give you an ideal
S/N of about 22, which is more than good enough to show a visible dot.
However, there are other noise sources not so easy to calculate, such as
dark current noise, readout noise, and sky noise. Considering all these,
there's a good chance that your 500 photons of signal might be dropping
down into the mud.

BTW, doesn't the SD1000 actually have a 15 second maximum exposure time?
That should be long enough to easily get a mag 5.8 object, even with the
increase in dark current noise.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
.

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