* Apr 6, 2003: fixed minor error in calculation of flux inside
small apertures *

* Mar 2, 2004: fixed another error in calculation of flux
inside very small apertures *

* Aug 30, 2004: now PSF centered on a pixel, rather than split at junction
of 4 pixels
*

This form allows you to calculate the signal-to-noise ratio for a star observed with a telescope and CCD. You can vary the parameters and find out what sort of results to expect.

Assumptions:

- the star has the same spectrum as Vega, so it will give inaccurate results for very cool, red stars.
- the sky has the same spectrum as Vega
- the extinction coefficients are typical for sea-level sites; unfilted observations are given the V-band extinction coefficient

If you want to see the calculations themselves, try reading the Perl source code to the calculator. Or, if you just want to see the equations governing the calculations, try this article by Steve Howell.

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Last updated Aug 30, 2004 by Michael Richmond.
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