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Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 23 > Chapter 6: Exposure Time Calculations > 6.3 Throughput and Sensitivity

So far, we have given the formulae for count rates in terms of the sensitivity (S). If you would like to use the throughput (T) rather than the sensitivity, you can use the following conversion equations.

•

•

• A is the area of an unobstructed 2.4 meter telescope (i.e., 45,239 cm2);

• h is Planck’s constant;

• c is the velocity of light;

• For spectroscopic modes, the transformation equation can be written as:

• d is the dispersion in Å/pix.

Space Telescope Imaging Spectrograph Instrument Handbook for Cycle 23 > Chapter 6: Exposure Time Calculations > 6.3 Throughput and Sensitivity