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5.9 Observing Hints

1. Request that your Instrument Assistant or Telescope Operator do a knife-edge telescope focus at the start of your run. Also do a telescope focus run using just the TV and compare the focus values. After a telescope move of 15-20 deg, refocus the telescope using the TV.

2. Cosmetically the F3KC chip is among the best CCDs we have. The area around 837,78 (in full format) is an area of depressed sensitivity and should be avoided.

3. To get a rough idea of your signal-to-noise, try the following. Do a row plot in the wavelength area of interest. Integrate the profile above bias with the "i" option in the cursor package. Multiply this by 2.8 electrons/ADU and by 3 pixels/resolution element (unbinned) to get the signal per resolution element. The square root of the signal SNR/res. element .

4. If you require the best radial velocity precision, take a wavelength calibration exposure before and after each object exposure at the object position.

5. As mentioned earlier, the spectrograph shutter takes a noticeable time to open/close. The actual time the shutter is open is 100-250 milliseconds shorter than the advertised time. Exposure times of a minimum of 20 seconds are suggested if 1% or better timing accuracy is desired.