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Wise Observatory Utilities
Signal to Noise (S/N) Calculator


The Signal to Noise calculator could be used for estimating the exposure time needed for imaging an object with a given S/N. The deafult values in the utility are for the Wise Observatory with the Textronics CCD camera but one can change this value to be usefull for other observatories and instruments.

The calculation is done for moonless night! Systenatic errors are not taken into account (e.g. FF color, etc.). The PSF is assumed to be a Gaussian.

Zero Point mag. ZP per
Gain electron/count Readout Noise electrons
Seeing (FWHM) arcsec CCD Scale arcsec/pixel
Aperture radius Aper. Units
Sky Backg. Area pixel2
Flat level Flat units
# of Flats images
Sky Brightness SB Units
Air Mass Extinction coefficient mag./airmass
# of Frames images Needed S/N
Object magnitude Saturation Level ADU

(Optional - Wise Camera setup) Choose Filter


Exposure Time Needed
Take images of Sec.
Point source brighter than are saturated (in each image - with 15bit depth)!



Constructed: April 1998, by: Eran Ofek , E-Mail: eran@wise.tau.ac.il