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QUCAM3 Parameters with UltraDAS + SDSU Gen.3

Device Identification

Chip name


Year of manufacture 2008
Serial number


First light on La Palma September 2008
Description E2V CCD201-20-4-122 Thinned midband AR coated. L3 electron multiplying CCD. Camera Picture
A paper on 'The use of electron-multiplying CCDs for astronomical spectroscopy' by S.Tulloch and V.Dhillon

Operational Characteristics

Speed Fast


Bias (ADU) 2400 1980
Gain (ADU/e) 0.0089 e/ADU 1e = 112 ADU 1.04 e/ADU
Read Noise (e) <1 4
L3 Gain 260 1

Recommended command for rapid spectroscopy is 'rmode spec'. This produces image sequences with very low timing jitter and supersedes the earlier 'rsrun' command.

'rmode spec' timings as follows:

Window size Fast Slow
Full fame 3.6s 5.0s
window = 1080 x 512 1.8s 3.0s
window = 1080 x 256 0.85s 1.45s
window = 1080 x 128 0.45s 0.75s

1) The chip has been reoriented such that the spectra now lie with the spectral axis horizontal. This allows use of horizontal windows which permits faster readout.

2) Windows should include the full width of the chip or the L3 gain will be reduced from the figures quoted above.

3) Please note that when using the 'rmode spec' command the actual exposure time will be the sum of the readout times (in the table above) and the requested exposure time. This is because the CCD is operated in frame transfer mode and the exposure time is effectively the cycle time of the system when making image sequences.For information on the rmode spec syntax click here.

4) If exposure times of less than the frame readout time are required then it is necessary to use the' multrun' command. This is not recommended however since it will be very wasteful of photons. Multruns issue a clear to the CCD before every exposure and for an equal sized window are 0.3s slower to readout than a frame taken using 'rsrun'.

5) Engineering note: If the observer definitely requires multrun with very short exposures (shorter than the mechanical shutter response time) it will be necessary to hold open the shutter using the manual switch on the front panel of the shutter rack and startup the observing system using a different version of the software.
In this case the cameras are instead called QUCAM2NS (or QUCAM3NS) and this name needs to appear in the configuration file.

6) 'whtdas14' or 'whtdas15' which have more RAM (2GB) than the other das machines should be used with the Qucams. The Linux PCs should not be used with either of the Qucams until further notice. This camera has now been commissioned with the new Linx PCs.

7) A reset of the controller including a dasreset should be avoided at all cost, it should certainly not be done during the DE checks, the result is increased dark current.

Linearity information here

Windowing : when used on ISIS the spectra will have the spectral axis along a row. Windowing in x may produce a reduction in gain and should not be used. Y windowing fully functional. The first 10-20 columns of an x-window will contain a large gradient. The bias in Y is very flat although the first row may contain some stray charge.

Binning :
Only possible in Y

Physical Characteristics

X Pixel size 13 microns

Y Pixel size

13 microns
X size in pixels of digitised area


Y size in pixels of digitised area


X size of useful imaging area


Y size of useful imaging area


X start of useful imaging area


Ystart of useful imaging area


Operational Parameters

Operating temperature

163K  (requires 3 hour cool down to stabilise at operational temp, important for gain stability)

Preferred Amplifier

Both are used depending on the readout speed

Measured Characteristics

Predicted QE

Clock induced charge 0.010 e/pixel/readout

Dark Current

5.3 e/pix per hour 1 hour after power on, falling to
<1 e/hour after 2 hours           

Notes on use of camera

This L3 camera also has a conventional output. The user can select L3 operation by using 'rspeed fast' and conventional operation using 'rspeed slow'. Since these two amplifiers are positioned at different corners of the CCD they will produce mirrored images. i.e. if the user changes the readout speed they will observe the image to become horizontally flipped.

For information on which of the 2 outputs to use see this document.

Some papers describing the use of L3 CCDs see this link
Sample Images and Observing tips for L3 Cameras see this link


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Last modified: 08 April 2011