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.

• USER> STATION PRIME
• USER> INSTRUMENT PFCCD
• USER> AGSELECT PRIME
• Zeroset AZ and ALT

• USER> AZ 298
• USER> ALT 89
• USER> ENG
• USER> ZERO AZ TAR
• USER> ZERO ALT TAR

Drive AZ and ALT slowly in + direction over the zeroset target points, then switch to computer control again

• USER> ZERO AZ ABS
• USER> ZERO ALT ABS

• USER> ZERO ROT ABS
• USER> WAVELENGTH 0.6
• USER> TEMP ...
• USER> PRESS ...
• USER> HUMI ...
• USER> UT1UTC ...
• USER> CAL LAST
• USER> FOCUS 86.55 (13/05/2005)

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.

SYS> 4MSControl.

The main use for this GUI is to change the filter in the science camera. Click on the tab "PFIP Observer" (opens by default) and underneath the button "Update filter list" there is a menu-bar with which you choose the filter. Next press the button with the wheel to actuate the move to the selected filter. A PDF document giving a complete list and description of the PFIP mechanism commands and new PFIP controller solaris software (PFIP GUI included) can be found here or through this link to the Instrument Page User Guide.

DETECTOR

X,Y axis shows direction star moves for a positive offset or aperture

  
Each CCD 2048x2048 pixels imagining area.

  
Scale: 0.24"/pixel

  
Rotator center aprox.2085,2028 on CCD1

  
AUTOGUIDER.

  

PGDY----> width 1500 units =25"

PGDX----> width 1500 units =25"

Filling the cryostat:

The cryostat is at prime focus so it is necesary to park the telescope at AP2.

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.

Rotator centre:
Without any aperture offset, the rotator center is very close to the gap between the two CCD's. Note that the imaging area on each chip extends from x = 53 to x = 2100. Below x=53 is the overscan region, this is electronically generated and no physical pixels correspond to this region.

Calibrate procedure:
As the rotator center is close to the gap between the two chips, calibrate is best done with a modified aperture 0 offset. Make sure to restore the original value after calibrate!

USER> enter ap 0 250 0 (rotator center will be close to center of CCD1)
USER> cal faint, then ^Z (go to the next faint calibrate star)
USER> rot sky 0
when in position take a short exposure and measure x and y within the defined window, reading out the center of chip 1.
USER> rot sky 180
when in position take a short exposure and measure x and y, then calculate the rotator center. This should be close to the center of chip 1.
USER> cal faint
take short exposures for all 7 stars, calculate offsets (in RaDec) with respect to the rotator center and input these in HANDSET mode.

Determine aperture offset:
In order to move the rotator center to the center (gap) between the two chips, aperture 0 had to be defined as -11.3 -6.7 (October 2002). If you need to define aperture 0, so the rotator center falls on the center of chip 1 or 2, you need to add +/- 250", (1024pixels+19.5pixels)*0.24"/pixel, this is half the size in x plus half the width of the gap:

CCD1: +250 0
CCD2: -250 0

Acquisition:

PFIP usually observes with a Rot Sky 0, so it is important to be sure that the rotator doesn`t reach the limit switch.
If requested to center the object on either of the CCD's instead of the center (gap) between the two chips, change aperture 0 by adding +/- 250" in x or define an additional aperture.
The MOUNT PA range is only 357 degree total, (limits: -163.37,193.63) hitting the limit you can't simply unwrap, you have to wait a certain time until you got past the 3 'forbidden' degrees, this may take a while, depending were the object is on the sky; therefore watch carefully what the limits are, each time you move to a new source!

Guiding:

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.

• The data may not all fit on one 4.7 GB DVD. Even 4.5 BG on disk will not write to 1 DVD.

-------- © 2005 Isaac Newton Group of Telescopes --------
Last Updated: 14 Oct 2007 Neil O'Mahony TOGnom_AT_ing.iac.es