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Home > Astronomy > Wide Field Camera > Detector Binning and Windowing

Detector Binning and Windowing

Binning is possible in all 4 CCDs and windowing on CCD4 only.

WFC binning can be set with the following commands:

      SYS> bin 1 1   (1x1 pixels, no binning, by default, pixel scale=0.33") 
      SYS> bin 2 2   (2x2 pixels, pixel scale 0.66")
      SYS> bin 3 3   (3x3 pixels, pixel scale 1.0")

Be aware that binning increases the noise by a factor of 2-5. For the last binning noise and gain values, please check the CCD Quality Control pages. The following plots show examples of binning and noise on CCD2:

CCD2 bin 2x2 slow
CCD2 bin 2x2 fast

Readout times for the whole 4 CCD mosaic for different binnings and readout speeds are provided in the following table:

NOTE: Please do not attempt to use the entire CCD4 as a window (with or without any binning option). This will crash the system.

WFC windowing is possible only on CCD 4. To set binning window [X1:X2,Y1:Y2] (with X and Y coordinates to cover the necessary region (CCD coordinates of chip #4) around the object, type:

       SYS>  window 4 '[X1:X2,Y1:Y2]'

where (X1,Y1) and (X2,Y2) are the physical corners of the window defined around the object. To disable this window, type:

       SYS>  window 4 disable

For example, to define a small central 1'x1' window in CCD4, one should use:

       SYS>  window 4 '[934:1114,1960:2140]'

To define a small central 5'x5' window in CCD4, one should use:

       SYS>  window 4 '[569:1479,1595:2505]'

While to define a central 10'x10' window in CCD4, one should use:

       SYS>  window 4 '[168:1988,1190:3010]'

NOTE: By defining a central window, the overscan information is lost. In order to keep the overscan, one should define the window close to the edge of the CCD4 overscan region BIASSEC='[10:2150,4105:4190]'.

For example, to define a 1'x1' which includes the overscan, one should use:

sys> window 4 '[934:1114,3830:4190]'

which includes in Y both the 180-pixel window and the original overscan from Y=4105 to 4190.

Once again, CCD4 is the only chip that can be windowed.

Moreover, one can define four different windows at the same time on CCD4 (provided they do not overlap), namely window 1, window 2, window 3 and window 4. Remember, these are not related with the four chips.

Regarding reading time for different size windows, we measured the following times in slow mode:

Whole CCD4  (2154x4200 pix) - 46 sec  
10'x10' FOV (1820x1820 pix) - 18 sec 
 5'x5'  FOV (910x910 pix)   -  6 sec 
 2'x2'  FOV (360x360 pix)   -  4 sec 
 1'x1'  FOV (180x180 pix)   -  3 sec
NOTE: Binning and windowing at the same time will cause the system to crash.

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Contact:  (WFC Instrument Specialist)
Last modified: 29 December 2023