1. POLARIMETRY: Using the same aperture for imaging-polarimetry and spectro-polarimetry; the former is measured and entered in the system. This means that with spec-pol acquisition the star in imaging mode will always be slightly off (posn angles of more than -90 will make things progressively worse!); UPICK at the scope will fix this, moving the target onto the slit..
2. CORONAGRAPH: Again, using the same aperture for pol and non-pol. Aperture should be measured (with all the other apertures), using the non-pol reference pixel listed below.
3. The arcsec values are simply the mm values times by -1.524
4. The first value is E-W, the second N-S, so in the rotated UIST frame the first value is along the slit (up and down, or in Y in pixels - see below)
5. The difference between apertures should be fixed (so strictly speaking we only need to measure two apertures - imaging at the two camera plate scales). Approximate relative offsets are:

 - Spectroscopy = Imaging(0.12arcsec) + 13.2, Imaging(0.12arcsec) + 2.6 
 - IFU          = Imaging(0.12arcsec) +  7.5, Imaging(0.12arcsec) + 2.0
 - Polarimetry  = Imaging(0.12arcsec) +   21, Imaging(0.12arcsec) + 1.5 
 - Coronograph  = Imaging(0.12arcsec) -   20, Imaging(0.12arcsec) + 32.5 

1. POLARIMETRY: The reference pixels for imaging-pol and spec-pol are measured WITHOUT the waveplate and wollaston prism in the beam. This is because we do imaging acquisition with spec-pol WITHOUT the prism in the beam. However...
2. CORONAGRAPH: The reference pixel for coronographic imaging POLARIMETRY is measured WITH the wollaston prism in the beam. This is so we have to do imaging acquisition with the wollaston in the beam (can't use the acquisition eyeball in the OT because this isn't spectroscopy!). NB: Should UPICK on the LOWER pol beam.

3. After the array was inverted in Jan '07, all values shifted by +8 in X, -40 in Y. For example, Spec-1-pix used to be 508,590. Imaging values are unchanged (Imaging pol has shifted because the mask is lower).

TTTs PLEASE NOTE: UPICK automatically applies the above offsets. TSSs do not have to adjust the source position after imaging acquisition in the thermal (this is why upick puts the star on a slightly different pixel than is listed earlier on this page).