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The following link has access to the exposure time calculator for Pisces diffraction limited mode:

This is version 1 of the ETC and it is not include the calculus of the strehl ratio versus the wavelength, start magnitude or separation of the reference AO star. This code is still in development and not yet fully verified against good observations. The following three plots can help to determine the expected strehl ratio of the observing target. This has to be checked before to set the parameters in the ETC. Please report any problem to Juan Carlos Guerra ( We want to give thanks to Andre Germeroth.

The ETC program has a fixed parameters as:

*Telescope transmission,light collecting area,reflectivity. *Transmission of the instrument(entrance window,lenses,collimator,filters,...) *Quantum efficiency of the array.

The efficiency of the camera in two wavelength regimes.
Filter H   Ks
efficiency 0.57   0.61

* The entrance window is placed in the rotator flange. It reflect the visible light to the wavefront sensor unit (W-Unit). * ETC applied a corrector factor calculated from the instrument zero point. This parameter has been calculated during a non-photometric night and this has to be updated during the coming observing nights.


Plot 1 shows the on-axis SR dependency with the seeing and the AO guide star magnitude. Plot of SR vs Magnitude-

Plot 2 shows the theoretical Fried approach of the variation of the SR with the distance from the AO guide star. Plot of SR vs Distance from AO guide star-

Plot 3 shows the changes of the on-axis SR with the wavelength. Plot of SR vs Wavelength-

  • Plot of Strehl Ratio versus guide star magnitude:

  • Plot of SR vs Distance from AO guide star:

  • Plot of SR vs Wavelength:
Topic revision: r9 - 03 Oct 2011, JuanGuerra
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