Aperture Offset

After the TO is finished CALIBRATE, you can do the APERTURE OFFSET.

• Use the last CALIBRATE star, making sure that the star is on the rotator center.
• The TO should type apoff handset on TCS to go into aperture offset mode (where telescope offsets are summed to give a final aperture offset).
• Start moving the mobile probe to 0,0 in AF2 xy coords by typing afvsky x y and then moving the telescope so that the star continues to be centered in the mobile probe window. You may have to do this in small steps (steps of 100-200 in AF2 xy coords works okay) For example, if the rotator center was determined to be at -500, 800, you might type afvsky -300 200 and then move the telescope to keep the star centered. Then afvsky -200 100 and so on, until you finally type afvsky 0 0 and centre the star in the mobile probe. The star is now at the AF2 center. The offset between the rotator center and AF2 centre during the May 1996 run was X=9 arcsec, Y=19 arcsec. If you feel confident (or you have determined the offset earlier in the run), you can just offset to the likely values and type afvsky 0 0 to see if you can see the star on the mobile probe, after which you can centre it up as before.
• Type store aperture 0 on the TCS. The aperture offset corresponding to the difference between the rotator position and the AF2 center has now been recorded. Now, when the telescope is pointed to an object, the aperture offset will automatically be done, and the object should be centred on the AF2 center, which is what you want.