DBS Signal-to-Noise Calculator

WARNING:

This calculator is computing results based on the old DBS detectors with 15µ pixels whereas the new detectors (see here and here) are 13µ and the sensitivities are different.

Blue Red

Grating

Grating Angle

Wavelength Å Å

Magnitude/Flux density

Sky Surface Brightness Blue Red

mag/arcsec²

Slit Width

Slit length on Object

Calculate S/N for Exp. Time

Exp. Time for S/N

Usage:

The signal to noise ratio, or exposure time, are calculated independently for the red and blue arms of the spectrograph. Simply enter the appropriate values and select the corresponding units. Any grating or dichroic combination that has not been calibrated cannot be used in the calculation. These are indicated by (NA). The grating angle is optional. If left blank, the wavelength is assumed to be the central wavelength. Entering a grating angle allows for an off-blaze throughput correction. For the sky flux, choose between flux densities at the central wavelength, or a broad band magnitude, by highlighting the corresponding button. The slit length and width are used to calculate the sky flux extracted with the object spectra, hence the slit length should be the spatial dimension of the object on the slit. Also choose between calculating an exposure time for a given signal to noise ratio, or the signal to noise achieved for a given exposure time. Click the CALC button when you're done. Should you get 0 electrons as a result, you're probably entered a wavelength for which the dichroic has zero efficiency.

Back to the Calculator

Written by Ian Price

Contributions by : Robert Smith, John Norris, Peter McGregor and Laura Stanford

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	Research School of Astronomy and Astrophysics Mount Stromlo and Siding Spring Observatories ANU College of Science