This page contains some frequently asked questions and their answers. Contributions and suggestions are encouraged, but make sure you have consulted the SofI user manual first.

  • Question: I want to obtain a spectrum along the major axis of my favorite galaxy NGC3947076. The position angle given in the catalog is 102.454 deg. What "Rotation Offset on the SKY" should I use?
  • Answer: The same as the position angle you have got from the catalog: 102.454 deg.
  • Question: What is the saturation limit of the SofI detector?
  • Answer: Actually, it is more important what is the limit up to which the detector's response is linear. The array non-linearity is less than 1.5% for signal up to 10000 a.d.u. Therefore, the users should plan their observations kepping the signal at the peak bellow this limit. At the minimum DIT of 1.182 sec, a ~10 mag star reaches it for seeing better than ~0.7 sec in any of the broad band filters. In such cases we can either defocuse the telescope (at the price of the image quality) ot switch to a mode with smaller pixel scale.
    Note that the Exposure Time Calculator gives the predicted signal in electrons, not in a.d.u. (1 a.d.u. is approximately 5.4 electrons).
    Note also that the sky in broad band imaging contributes lot! In K-band, large field mode, this is 400-700 a.d.u./sec, depending on the humidity and the temperature.