|Home > Astronomy > Telescope Operator Notes > Working with Old Prime Focus|
WORKING WITH OLD PRIME FOCUS
PFIP (PRIME FOCUS IMAGING PLATFORM) is currently undergoing major changes to the camera hardware and hence most of this page no longer applies to the new imager. These notes will be kept until the old PFIP camera is phased out completely.
PFIP houses an optical mosaic camera consisting of 2 EEV 2kx4k CCDs, giving a pixel scale of 0.24" and a field of view 16.2'x16.2' (with a gap between the two chips of 9"). PFIP is an instrument platform that replaces the secondary mirror.
Drive AZ and ALT slowly in + direction over the zeroset target points, then switch to computer control again
The light to the autoguider is fed by a fiber, giving a FOV (25"x25"). Use in twilight to define the AG window.
Use the standard uDAS autoguider from leo (whtdas3) with 'obssys 1', 'startobssys' and 'startag AG1' followed by 'option 3'. DS9 display tool will also appear as well as the TV Guider Control. This box allows you to change exposure times, take fields and set the TV and Guider going. Images are piped directly to the display tool. GSS2 is used for finding guide stars. On OSADISPLAY2 open GSS2 using the icon on the desktop, select WHTPrime and include any offsets applied.
From the observer interface the autoguider probe can be moved, the control GUI starts using the command from the SYS or TO prompt. The obssys brings up one such GUI on WHTICSDISPLAY but the TO can bring up another one on the taurus session. It is useful for controlling Autoguider probes and focus. The probe response is faster on this GUI than when using the command line.
These diagrams show the direction in which the star moves for a given X or Y telescope movement or a given autoguider probe movement: The CCD gap is about 39 pixels.
X,Y axis shows direction star moves for a positive offset or aperture
PGDY----> width 1500 units =25" PGDX----> width 1500 units =25"
Filling the cryostat:
From the TCS:
USER>DOME 298 (this is important to prevent water dripping from the edges of the shutter onto the camera electronics in wet conditions)
USER>ROT MOUNT -75 (FILLER TUBE AT TOP)
USER>AZ 298, EL:15
When the telescope has stopped change to ENGINEERING mode and go up to the telescope and move it manually to AP2. After filling the cryostat move the telescope out of access park by pressing ZP. Go back to the control room and switch back to COMPUTING mode.
USER> enter ap 0 250 0 (rotator center will be close to center
Determine aperture offset:
CCD1: +250 0
PFIP usually observes with a Rot Sky 0,
so it is important to be sure that the rotator doesn`t reach the limit switch.
Open a terminal, logon as whtobs and type 'obssys' followed by the correct option. From this TO-window the probe is moved with command 'agprobe' and the guider focus with 'agfocus'. Focus was around 7877 (Nov 2012). 'pfip_status' lists the status.
GSS search results require little or no correction, even when an APERTURE OFFSET is included. GSS was 100% correct at ROT SKY 0 including apertures. Other angles than ROT SKY 0 have not been tested, but there is a good chance that GSS will also work there.
Dithering while keeping the guide star:
The observer will usually use the OFFSET ARC command to make a dither pattern. Even a dither of 10 arcsec will require adjusting the guide probe position because the star image is so large compared with the Guider field (unless you are clever enough to place the star in the correct corner and make a 4-point square dither pattern). Basically for every 10 arcsec offset, you need to move the probe 600 units. A telescope offset in +X will require a probe offset in +X, but a Y offset requires the probe to be offset in the opposite Y direction to recapture the star.
-------- © 2005 Isaac Newton Group of Telescopes --------
|Top | Back|