[ ESO ] La Silla


La Silla Science Operations: NTT

EMMI Imaging Characteristics



Imaging with EMMI can be done with both the RILD and the BIMG modes, respectively for red (lambda > 400 nm) and blue (lambda < 500 nm) observations. The following figures illustrate the light paths.

For the Red CCD, to avoid that the main object falls in the inter-chips gap, the mosaic has been slightly shifted in the dewar so the target will fall in the area of the master chip (right-hand side of the mosaic).

Other effects to keep in mind for the Red CCD are translation, rotation and astrometry.


Red CCD: Translation

The slave ship is translated with respect to the master (note: the master chip is Zeus):

x(master) - x(slave) = 27.0 pixels = 4.5''
y(master) - y (slave) = -2.6 pixels = 0.43''
This effect is corrected by the software, adjusting the number of pre-scan column on each chip. Joining the 4 sub-images will produce an image geometrically correct within 1 pixel in the central region (y ~ 2000). The geometric error goes up to 2 pixels at the top and the bottom of the gap.


Red CCD: Rotation

Delta X = 0.90 pixels over 4000 pixels
Delta Y = 0.35 pixels over 4000 pixels

These values correspond to a rotation of 0.22 mrad. This is a physical rotation of the CCD, so no correction is possible.


Red CCD: Astrometry

An estimate of the astrometric transformation has been determined for both chips:

Master chip (right hand side one):
   d (alpha) = cost + 0.046274x + 0.000144y + 0.000002xy + 0.000024x^2 - 0.000014y^2
   d (delta) = cost - 0.000029x - 0.046179y - 0.000044xy + 0.000039x^2 - 0.000019y^2  
Slave chip (left hand side one):
d (alpha) = cost + 0.046489x + 0.000139y + 0.000000xy - 0.000018x^2 - 0.000005y^2
d (delta) = cost - 0.000050x - 0.046299y - 0.000009xy + 0.000004x^2 - 0.000003y^2

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