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VIMOS Quality Control:
MOS mask to CCD transformation

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Trending & QC1
   MOS mask2CCD
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QC links:
mask to CCD transformation | focus
X0 and Y0
translational matrix coefficients
rotational matrix coefficients plot plot
image quality plot plot
ellipticity plot plot
QC1 database (advanced users): browse | plot
   Click on CURRENT to see the current trending (Health Check).
   Click on HISTORY to see the historical evolution of the trending.

The Mask to CCD Transformation Matrix translates mask coordinates into CCD pixels. It is determined with special MOS masks having pinholes on a regular grid. Measurements using these mask are typically executed once a day for health check purposes. Since August 2010, these frames are also used to check the VIMOS focus.

Example MOS pinhole mask image


top Mask to CCD transformation parameters

The transformation matrix has the following form:

X = a_xx * x + a_xy * y + x_0
Y = a_yx * x + a_yy * y + y_0

with (x,y) being mask coordinates in mm and (X,Y) CCD coordinates in pixels. X direction is along the slit orientation, y direction is perpendicular to the slits (i.e. in dispersion direction).

The matrix coefficients a_xx, etc. and the zeropoints x_0 and y_0 are determined from the pinhole image for each quadrant. The diagonal coefficients a_xx and a_yy give the scale factor between mask and CCD (around 8.4 pixels/mm). The coefficients a_xy and a_yx give the rotation and are nearly zero.

QC1 parameters

parameter QC1 database: table, name procedure
x_0 vimos_mask2ccd, x0 x0 coefficient of mask to CCD transformation
y_0 vimos_mask2ccd, y0 y0 coefficient of mask to CCD transformation
a_xx vimos_mask2ccd, xx xx coefficient of mask to CCD transformation
a_xy vimos_mask2ccd, xy xy coefficient of mask to CCD transformation
a_yy vimos_mask2ccd, yy yy coefficient of mask to CCD transformation
a_yx vimos_mask2ccd, yx yx coefficient of mask to CCD transformation


top Focus QC parameters

From the pinhole images, also QC parameters for checking the focus are calculated. These are image quality (as FWHM in pixels of the major axis fo the pinhole ellipses), ellipticity, and orientation (of the pinhole ellipses). Each quadrant is divided into 3x3 sub cells (squares). All parameters and their standard deviations are calculated in each cell and globally per quadrant.

QC1 parameters

parameter QC1 database: table, name procedure
pinhole_count vimos_mask2ccd, pinhole_count total number of identified pinholes per quadrant
image_quality_mean vimos_mask2ccd, image_quality_mean averaged image quality per quadrant
image_quality_rms vimos_mask2ccd, image_quality_rms standard deviation of image quality per quadrant
ellipticity_mean vimos_mask2ccd, ellipticity_mean averaged ellipticity per quadrant
ellipticity_rms vimos_mask2ccd, ellipticity_rms standard deviation of image quality per quadrant
orientation_mean vimos_mask2ccd, orientation_mean averaged orientation of pinhole ellipses per quadrant
orientation_rms vimos_mask2ccd, orientation_rms standard deviation of orientation per quadrant
iq_mean_cell[1-9] vimos_mask2ccd, iq_mean_cell[1-9] averaged image quality in each cell (per quadrant)
iq_rms_cell[1-9] vimos_mask2ccd, iq_rms_cell[1-9] standard deviation of image quality in each cell
ellip_mean_cell[1-9] vimos_mask2ccd, ellip_mean_cell[1-9] averaged ellipticity in each cell
ellip_rms_cell[1-9] vimos_mask2ccd, ellip_rms_cell[1-9] standard deviation of ellipticity in each cell
orient_mean_cell[1-9] vimos_mask2ccd, orient_mean_cell[1-9] averaged orientation in each cell
orient_rms_cell[1-9] vimos_mask2ccd, orient_rms_cell[1-9] standard deviation of orientation in each cell


date event
2011-05 tilt between focal plane and detector plane fixed, image quality and ellipticity improved; there is, however, a dependency between ellipticity and temperature
2011-08-27 Q3 out of focus, fixed 2011-09-06