WeDoWo polarimetry supposes the one shot imaging procedure, very easy and quick to perform if a good flat field and a good zero polarization standard has been obtained. It is useful in the case you are interested to observe a star object with only one shoot.

Imaging

With the 10 arc-second slit the FOV is 10 arcsec times the length of the slit.

Set the CCD Window (afternoon by the observer):

select 10 arc sec horizontal slit
select WeDoWo (in grism wheel)
make sure all the other wheel positions are open and no other optical elements in the beam
turn on the ThAr calibration lamp
take a 0.3 sec image and note the ysize and ybeg and possibly xsize and xbeg for the polarimetry window about ysize=400 and ybeg=820
if you keep the full xsize the benefit is having pre/overscn in the frame

Calibrations:

Day time
- take a dome flat fields (10 images for example) with slit/polarimetric mask, filter and polarimeter inserted with rot-pos 0 deg and
  second set with rot-pos 90 deg
  - put the halogen "Dome FF Lamp" under the telescope
  - power-on the telescope
  - open mirror covers
  - set the telescope to altitude 45 or so, (TCS alt 45)
  - for blue or narrow filters open sideports, note only when the weather allows (no rain, humidity less than 90%)
  - take the data
night time
- low polarization standards in order to estimate instrumental polarization
- high polarization standards in order to estimate the position angle zero point

Note that it is recommended to take the polarization standards with the same field-rotation angle as your science frames.

Telescope focus:

The best focus with the "WeDoWo+ no filter" is about +40 TCS focus units greater ('tcs.foc-del +40') than the one with "no filter".

Target acquisition:

take a target acquisition image with the required filter in the beam
offset the telescope
take a second image with the WeDoWo in the beam for fine tuning the position and estimating the needed integration time.
For target acquisition you can use "alfosc.acquisition" script e.g.
tessa$ alfosc.acquisition -q Slit_10.0 2
tessa$ alfosc.resetxy
tessa$ alfosc.ysize 400
tessa$ alfosc.ybeg 820
tessa$ alfosc.wheels -g WeDoWo
tessa$ alfosc.expose 10
If you want to have two targets on the slit use "alfosc.slitrot"

Imaging Setup (by staff):

10 arc sec horizontal slit in the aperture wheel
WeDoWo in the grism wheel, in such way that the image is split vertically (see image)
use broad band filters either in FASU or filter wheel.

The WeDoWo should be installed in the grism wheel in such a way that it splits the beam vertically. When inserting it in the slot, the element's dividing line should be horizontal. Install the 10 arc-second wide slit horizontally in the aperture wheel. In editsetup select WeDoWo with orientation Horizontal and and Slit_10.0" with orientation Horizontal.