CCDT150 and CCDT90 Cameras

Andor ikon-L CCD cameras (model DZ936N-BEX2-DD) are available at the Nasmyth East focus of the T150 telescope and the West focus of the T90 telescope from July 2018 and October 2021, respectively. Both cameras are identical. They are deep-depletion CCD cameras with back-illuminated chip type, high quantum efficiency (> 90%) in the spectral range from 400nm to 850nm and are free of fringing effect. In addition, the chambers include thermoelectric cooling down to -80°C with air alone, minimizing dark current without the need for LN2. To reach lower temperatures, we have chiller or coolant dispensers, which allow to reach -100ºC.

General characteristics

Array 2048 x 2048
Pixel size 13.5 µm x 13.5 µm 
Scale T150: 0,232 "/pixel ; T90: 0,387"/pixel
FoV T150: 7,92' x 7,92' ; T90: 13,20' x 13,20'
Read-out time (fast mode) 4 s (binning 1x1); 1,5 s (binning 2x2)
Read-out time (low mode) 91 s (binning 1x1); 25 s (binning 2x2)
Gain (*) 4,0 e¯/ADU
Read noise 7 e¯ rms @ 1MHz
Dark current 0,006 e¯/pixel/s (@-80° C)
Orientation North-Up, East-Left
Lineality see Figure below

(*) Current Configuration: readout velocity 1MHz, gain x1 and 'High Sensibility' mode

Important notes and advices

  • If seeing is bad, binning will be advisable for most applications, in order to improve the signal to noise ratio and also in order to decrease the amount of disk space needed as well as to minimize the overheads (time lost in the CCD readouts).

  • The sky flat-field frames should be taken in the high speed mode because the photon shot noise will be one or two orders of magnitude larger than the readout noise and there will be no clear advantage in using the slow readout mode. This allows one to save valuable time at dusk, when light intensity falls rapidly and one may run out of time to do the flats with the narrowest filters.

  • The flat-field frames can be obtained at the highest resolution mode and later on degraded with software binning to the resolution needed for the different binning configurations.

  • The bias level is different for the different binning configurations possible. Therefore, one should take bias frames in all the binning configurations that one expects to use (typically 1x1 and 2x2).

  • Bias frames should be taken regularly along the observing night. This is advisable because the CCD chip does not have an overscan region. Changes in the bias level above 3 ADUs have not been observed, but just in case, one should take several bias frames per night. This can be done while moving the telescope to another target and will not waste any time.

  • The shutter is an iris shutter of 30mm in diameter. It takes 40ms in opening and closing. For special applications in which a fast sampling speed is needed, the shutter can be kept open in order to avoid the dead time and avoid wear of the shutter. This may be useful for occultation or time critical observations.

  • Currently, the vignetting is a 10% decrease in intensity exists in two of the corners of the chip, very likely due to an insufficient size of the holes of the filter wheel. This is a very small, unimportant vignetting, and can be compensated for by flat fielding. Therefore, it only implies a loss of signal in the order of 10 to 20% within an extension of the order of 1 arcmin.

As the Figure shows, the noise for bias is 1.35 counts and 2.50 at 50KHz and 1MHz respectively, both with 2x2 binning and without binning. The noise for darks with an integration time of 900s and a temperature of -85º is:
- 2.50 counts with 1MHz and 1x1 binning (same as bias).
- 2.80 counts with 1MHz and binning 2x2 (only 0.3 counts more than in the bias)
-1.37 counts with 1MHz and binning 1x1 (same as bias)
-1.66 counts with 1MHz and binning 2x2 (only 0.3 counts more than in bias)
Conclusion: At -85º, thermal noise is much lower than read noise and in practice negligible.
As a general rule of thumb for most observation programs, images can be taken with 1MHz, gain x1 and binning 2x2 with a readout time of 1s. For very faint objects requiring high exposure times (300s or more), images can be taken with 50KHz, gain x1 and binning 2x2 with a readout time of 25s.
The High Capacity mode is equivalent to dividing by 5 the number of counts at each gain, so it can be used to observe very bright objects without reaching saturation. For very bright objects, the best setting is 1MHz, gain x1, and binning 2x2, or binning 1x1 for the brightest objects.


The filter wheel provides six positions for 50mm square filters.

Available filters