INT WFC User Notes

Nic Walton/Juerg Rey/Mike Irwin/Peter Bunclark   - 25 May 1998

(This page will be webified in the near future - NAW) 

cryostat: WFC with 4 thinned EEV chips (2048x4100) and a thinned LORAL 
(2048x2048) chip for guiding.

system:   INT 
	+ WFC 
	+ CCD autoguider (LPVME01) 
	+ new DAS (LPSS13+LPSS15) 
	+ alpha TCS (LPSA2) 
	+ data reduction (LPSS14)

Machines used
lpss13:		the observing system Sparc20	(login as intobs)
lpss14:		the data reduction Sparc20	(login as intguest)
lpx22:		the TO xterminal
lpas2:		the INT DEC alpha TCS machine	(login as int_login)
lpss15:         the data aquisition computer    (should not need to login
                                                 -left logged on but...)

If lpss15 isn't logged on - login as intobs; usual password, then type
  > obssys
    choose the appropriate system, in this case option
	(WFC+ALPHA TCS+VME A/G (eg. s6-1))
  > startobssys  (at the moment DAS1,3,4 and 5 are used, the fifo on
                 the DATACELL card for DAS2 is defunct)

if all goes well you should see
dasload: Loading DAS1
dasload: Loading DAS3
dasload: Loading DAS4
dasload: Loading DAS5
and "ready to serve" messages shooting past

NB. DAS2 ne marche pas so we are using DAS5 instead.
    Normally this is left up and running so you don't need to do this


1.  on lpx22 open up a telnet window and connect to lpas2

2.  login to lpas2 as int_login (password available in the control room)

3.  select from menu "start"
	this starts up two other windows, the infodisplay and the user
        interface window, the original window continues being active as the
        telescope d-task window; be patient this takes a few seconds

[as of **19 may 1998** the teld window hangs - hence wait fro it to timeout,
then relogin to lpas2, login as int_login, select options then teld,
this starts the teld link up, minimise the window]


4.  login to lpss13 as intobs (usual password) (from the console -
	NOT through telnet)

5.  in the 'Observing system' xterm type		

  SYS> obssys   - defines appropriate procedures, aliases etc...

    choose the appropriate system, in this case option
      (WFC+ALPHA TCS+VME A/G (eg. s6-1)), then type

  SYS> startobssys

With startobssys both the TO and the observer sessions will be started.
You will get two autoguider windows, both of which are active, so both TO
and observer can control the autoguider at any time (simultaneously !$#@)
[NB. The autoguider appears to  be more reliable using the CLI commands rather 
than the buttons on the GUI.]

6.  lpss13 should now have the following observing system windows up:
WFC GUI  mouse control of the WFC where if you cannot type but can drive
         a mouse you can run the observing system  
         [NB. check that the MCA/MOSAIC/DAS1/DAS2/DAS3/DAS4/TCS/AUTO 
          items are green for go]

AUTODISP the autoguider gui
INFODISP telescope information display mimic

TALKER   the talker log - gives updated diagnostics of what is going on and 
         useful to keep visible to check on system status,

LOG      the observing log - the automatic observing sequence log 
         [****warning the autologger occassionally misses exposures]

the original "pink" SYS> xterm window is the CLI (command line interface) 
alternative to the gui but also has enabled a large number of extra commands.

To exit cleanly from a session on LPSS13

>shutdownobssys   -  answering [Y] tothe prompt about the wiping the system
                     removes all observer-related DA processes running on
                     LPSS13, including the TOG AG display and DAS mimic etc..

[NB.  If you are unsure about state of LPSS13 regarding leftover observing
processes >cleanup in "pink" CLI window will check to see if any left and 
remove them.]

7.  Enable the WFC gui by clicking on the enable button (top right)
    and set the WFC CCDS to standard/slow readout speed by clicking on the 
    "standard/slow" button; and flash on the "clear speed" button.

  [NB. if a subsystem such as TCS or AUTO or DAS fails to come up (no green
   light on MOSAIC mimic), try startobssys again ...and again...and again...]

8.  On the TO xterm open a terminal session and login to lpss13.roque as
    intobs (usual password) and type

  intobs@lpss13> obssys

    choose the appropriate system, in this case option
      (WFC+ALPHA TCS+VME A/G (eg. s6-1)),

    in the TO 'Observing system' xterm; the prompt will change to TO> 

   (note: startobssys needs to have been already run on lpss13)

9.  Check the TCS INFO display to see whether the TCS has been setup
    for Prime (can use the TCS command SHOW FOCALSTATION) 

    if the TCS says that it is at Cass (check the TCS INFO DISPLAY window)
    or if the TCS configuration has not been loaded from the ICS for some
    strange reason, the following must be entered into the TCS directly:

  [NB. although startobssy probably failed miserably and it is best to try
   that again ...]

  USER> show focal 

  should report:

  	station prime
	instrument wfc
	agselect prime
  as these are sent by the startobssys procedure (which defines focal
  stations etc)
    check if aperture offsets are entered by typing

  USER> show aper

    the offsets below should be listed.  If not type as below:

  USER>	enter ap 0 -251   326   nominal aperture, object centered on CCD#4
        enter ap 1  704     5   center object on CCD#1
	enter ap 2  357 -1043   center object on CCD#2
	enter ap 3 -701   -10   center object on CCD#3
        enter ap 4    0     0   nominal aperture, object centered on CCD#4
	enter ap 5 1316  -368   center object on AG-CCD (X=1032, Y=512)
        enter ap 6  251  -326   center object on RC (rotator center)

10. Zeroset the telescope

  USER>	zeroset ha  tar
	zeroset dec tar

  (move the tel in engineering in slow motion over the target points
  close to zenith)

  successful zeroset is reported at the TCS console as zeroset complete

  at this point go into COMPUTER MODE (turn the key)
  USER>	focus 46.00	(this is the default focus value)

  	(note: the focus here includes all corrections for temperature
	and filter offsets)

  USER> cal last

11. Twilight flats

        there is now an automatic procedure which by continually reading
        the autoguider chip tells the observer what exposure time to
        use in order to achieve about 20000 counts. The observer types

	the telescope has to be tracking (goto a blank field or some
	other field)

   SYS> guide on pixel 1032 512    - to start the autoguider 
				     in continuous readout

   SYS> smartflat &

        a dialog box will pop up and tell the observer the needed
        exposure time, by simply clicking the `take this flat' button:
	the exposure will be made

	once all twilight flats are done, type

   SYS> guide off

12. Calibrating the pointing

	calibrate should only be done with the autoguider, type

    TO> agwin acq pos 1032 512

	use the faint pointing grid, narrow band filter if available, and
        make sure the shutter is ****OPEN****

  USER>	temp 6.7
	press 770
	humi 0.1
	wave 0.65		(example for Halpha narrow band filter
                                 if you use B then type 'wave 0.45')
  Single star "snafu"	

  USER> gocat 08+30     - or whatever pointing grid star is near zenith
  USER> aper 5
	on the autoguider mark the window center 
	use the menu items on the autoguider GUI (SETUP/TOGGLE CENTER CROSS)

	make sure that the guiding is OFF (remember to turn off after flats!)

    TO> autotv on       turns on continuous readout mode for autoguider    

        use "handset" to centre star on cross (in RaDec mode for the 180 deg.
        rotator position the cursors are reversed)

  USER> point calibrate
  USER> cal anal zero
        if solution ok type "Y"

a) manually calibrating the pointing, this is SLOW:

  Seven star manual calibrate - should not be necessary, so - 
  continue with b) autocal!

	within normal calibrate you can't apply AP5 to move the stars to the
	autoguider, hence you have to redefine AP 0 to be
  USER>	enter ap 0 1065 -42	(the sum of the nominal AP 0 and AP 5)
	before you start calibrate you enter the parameter which affect
	the calculation for the atmospheric refraction e.g.

  USER>	cal faint
	note the values in the log book, were we used to note down the SNAFU
	result and set the nominal aperture back to the default

  ****IMPORTANT**** remember to
  USER>	enter ap 0 -251 326     after finishing

b) automatic calibration of pointing, this is FAST: (say 20mins)

  Seven star calibrate

    TO> autotv off
    TO> autocal         this takes a few minutes per star
  USER> cal anal

        if solution ok type "Y"

13. Focusing:

        as on the WHT the temperature compensation and the differential
	focus (filters thickness) are kept apart from the nominal telescope
	focus, hence you should always find the best focus is close to 46.0
	when working with the alphaTCS.
        You can determine the telescope focus using either the autoguider
        or the science array.

a. Using the autoguider: find an 11th-13th magnitude guide star using

    TO> gsc_apm RaDec="10 30 0 30 0 0" Rotpos=180 Equinox=J2000 Beam=N
or SYS>

	select a 5s integration time either on GUI or by typing
    TO> autotime 5000  - units here are in msec

    TO> guide on pixel x y    - where x y are listed in gsc_apm

[or you can do it the hard way by
    TO> field
        guide on star 2  ]

        click view option on autoguider GUI and select starlog
        now monitor peak intensity of image from starlog whilst trying
        different focii eg. SYS or TO or USER> focus 45.9
        Best focus for autoguider is when peak intensity is maximised
        which also should be when image ellipticity is close to zero.

	The science array focus appears to be best when set 0.05 less
        than the best focus for the autoguider [but needs checking in
        stable sub-arcsec seeing - if you ever get any]

        guide off

b. Using the science array:

        to determine the telescope focus the observer should select a
        stuiable field (eg. one of the WFC photometric standard fields)
	and go to it eg....

   SYS> gocat sa101-427

   SYS> focusrun &

        a dialog box will pop up and the appropriate values may be filled in
        and a focusrun started.  All "#n" exposures will be taken on the
        same frame with the a double spacing between #1 and #2.

        [all the science chips are co-planar to +/- 25 microns, but see
         the model on the wall for more details or see blue WFC folder] 

        Remember to set focus to the best value at end of focusrun and
        if you want the original target back in the centre type another

14. Observing.

a. Object catalogues

User defined object catalogues are stored in the directory /int/cat
(on lpss13 or lpss14 as of 19980417) with the .cat ending
eg. and can then be "included" at the TCS USER
interface. eg......

  USER> incl messier

To view and manipulate the catalogue use the normal unix tools eg.
"more", "cat", "emacs" or if you want to add objects to it without
using an editor at the xterm CLI type

   SYS> object name 12 20 30 -10 5 40 J2000
   SYS> add

and go to the object by typing

   SYS> next   - for the last one entered or
   SYS> gocat name

However, objects added with the object/add sequence are passed
directly to the object catalogue held on the TCS computer, and are not
stored on the system computer

On the TCS computer, catalogues can be loaded from the system computer
with the INCLUDE command e.g.
  USER> include messier

The catalogue can be displayed with:

  USER> output term

or written back to disk with:

  USER> output file int:[cat]newfile

which saves the file on a disk also visible to the system
computer as /int/cat

b. Use MOASAIC GUI to observe or

c. Use CLI commands 

TCS/AutoGuider interface commands:

SYS> focus 46.0             - set telescope focus [default best focus]

SYS> rotate sky 180         - move PF rotator to 180 degrees [default]

SYS> gocat 12+30            - go to pointing grid star assuming

SYS> offset arc -30 30      - offsets telescope from current pointing
                              by -30 and 30 arcsec

SYS> autotv [on|off]        - continous readout mode

SYS> field                  - do a field and search for potential guide objects

SYS> guide on star n        - pick "n"th brightest detected object and guide

SYS> guide on pixel x y     - guide on at position x,y on autoguider CCD
                              default is to specify x y = -1 -1 which
                              cause A/G to guide on current guide star 
SYS> guide off              - turn guiding off
SYS> agwin acq pos x y      - set centre of field window for aquisition

SYS> autotime t             - set integration time "t" in ms.

If you accidently kill the AG display window you can restart it from the
CLI by typing

SYS> autodisp AUTODISP-TO & - assuming nothing else has fu'd.
       or AUTODISP-SYS &

Observing commands:

SYS> filter R               - change to R filter
   > run exp-time ["title"] - do a science run
   > bias                   - take a bias frame
   > glance                 - glance frame
   > abort                  - terminates active run without saving data
	                        but have to wait for readout to finish
                                if you aborted a readout
   > finish                 - terminate exposure and readout

Automated observing:

to get the gsc_apm programme to automatically predict guide star
positions when you move to a new object:


	gocat name 

commands will show guide star positions in the TALKER window. You can
then take these and start guiding with:

	guide on pixel x y 	(with x y taken from the prediction)

for real automated observing --->

See scripts in /home/intobs/*_s (also in /home/mike)

A: dither_example_s

# This "dithers" consecutive exposures in a spiral pattern with grid
# spacing of 2 arcsec 
# You could aquire automatically - see auto_example_s - but this
# assumes you have done a "gocat" and run gsc_apm to select a
# suitable guide star.  Make sure you do not spiral out of the guide
# window - set to be 37" x 37" in agwin.....command

B: photom_example_s

for automatic photometry observing

C:  auto_example_s

# This script only works for aperture 0
# Objects have to already be in TCS input catalogue
# eg. >object name 10 11 12 -1 2 3 J2000
#     >add

this script will go to an object, get the guide star, lock on and
start guiding, then run through the sequence of observations that the
observer has defined. 

Use these as examples - generate you own by using the examples as
templates - give them a unique name, remember to make them executable
by chmod u+x script.

then just type its name, and off the system goes. 


a.  Autoguider

If you lose control of the autoguider during a field or tv operation try typing

    TO> taskclose FIELD (or AUTOTV) or kill the appropriate process
                                       (ps; kill nnnn)

if this fails to recoup control, or in general with any autoguider problem:
first make sure any science exposure is finished; and then
reboot the autoguider by typing

    TO> telnet lpvme01
    Autoguider --> reboot (wait now for 'connection closed by foreign host')

    TO> tip agvme
    Autiguider --> reboot (wait for ....OK)
    Autoguider --> ~.

now type

    TO> startobssys
or SYS>

Startobssys will auto-detect the parts of the observing system still running
and so only restart what is missing. AT NO STAGE TYPE CLEANUP.

[Occassionally it may be necessary to phyically restart the VME autoguider
system.  Go to CLIP centre and press the red reset button on the autoguider 
VME crate (you may as well toggle the reset switch on the AG controller 
crate above it).  DON'T do this if you are unsure about which crate it is 
- there is a large choice of systems you can screw up.

Next wait 1 minute for VME sub-system to come up (or walk slowly up stairs)
and bring the rest of the system up usnig a "startobssys" on lpss13.]

b.  Tasks hanging

If a run task on the MOSAIC gui hangs or one on the CLI hangs first try the 
"abort" command or button.  If this fails then go to "pink" CLI window and 
"kill" the wfcrun(flat|bias|glance) process.  If this fails give up
and type "shutdownobssys" followed by "startobssys".

c.  DAS on LPSS15

If at anytime you need to clear corrupted or stuck DAS operations that
cannot be cleared using shutdownobssys and startobssys then you will need
to type
  > dasreset    - on LPSS15 or (if DRAMA fails):

  > cleanup     
  > foxreset    
  > dasload                                                ]

followed by "startobssys" on lpss13.

d.  Most normal screwups can be cleared by typing

 SYS> shutdownobssys - and answering 'Y' to the wiping question and then
 SYS> startobssys

e. The comms links to the autoguider and MCA go via two digiport servers, one
in the CLIP centre and the other on the CASS station of the telescope.
If you suspect the comms links  to either the autoguider or the MCA and
science controller are not working first try:

>tip meng          - to connect to Science CCDs controller

This will either "connect" successfully in which case type "~." to quit
or it will return with "link not available".  Likewise 

>tip ageng         - to connect to AG CCD controller 

>tip agvme         - to connect to AG VME crate

will show whether or not comms link is alive or alternatively whether 
VME crate is stuffed.

>ping - checks if CASS station digiport server is alive
>ping - checks if CLIP centre digiport server is alive

f. the tasks are working but the WFC GUI doesn't update - e.g. not all
the green lights come on for the CCD parameters:

	try:	taskclose MOSAIC	(for the CCD)

   bring the GUI down (use the window manager QUIT) then startobssys

g. Read the "talker" messages they tell you what is happenning.
   Read Guy's notes on recovering from a DRAMA crisis.

Finally if you are unsure about any of the preceding recovery procedures 
call for TO, SA or DT support.


for autoguider problems ...

If really stuck, and all else fails - to recover system try - in this

on TO system - logout of lpss13 and close/exit the autoguider GUI

on lpss13, 	shutdownobssys, logoff machine completely
on lpss15, 	shutdownobssys

tip into agvme, reboot, ~. to exit back to telnet (this reboots the

then: log onto lpss15 as intobs
	obssys - option 1 for WFC say
	startobssys		(loads the DAS tasks)

next: log onto lpss13 as intobs
	startobssys		(wait till completion)

on TO terminal get telnet window to lpss13
	logon as intobs
	obssys			(no need for startobssys)


	chip#1:		Ra -5"    Dec  704"	move telescope W and N
	chip#2:		Ra 1043"  Dec  357"	move telescope E and N
	chip#3:		Ra 10"    Dec -701"	move telescope E and S
	chip#4:         Ra  0"    Dec    0"
	(this is only valid for rot mount 180)

          | #3  0.33"/pixel  |				
          |                  |
          |                  |
          |                  |
          | #4               || #2       |
          |                  ||          |
        E |              RC  ||          |
          |               +  ||          |
          +------------------+|          |
          +------------------+|          |
          | #1               ||          |
          |                  ||          |
          |                  ||          |
          |                  ||          |
                     |    #AG    |
		     |           |
		     |  0.37"/p  |
                     |  Masked   |
                     | for frame |
                     | transfer  |

The above layout is for Rotator at 180 deg.

For Rot 270 the layout is		N
				    333344441111 AGAG
				E   333344441111 AGAG
				    333344441111 AGAG

Closed loop offsets
        If you are asked to offset by some arcseconds you may do this
	without opening the guide loop using either aperture offsets
        on the handset or you can use the "tweak" command

	10 arcsec correspond to 27 pixels on the A/G (0.37"/pix) so you
	need a guide window which can cope with the offset.
	The maximum window size I used so far was 160x160, with bigger
	window sizes I got 'missing pixel' messages.
        Below you find how the star on the AG will move using the XY handset.

	rot mount 180   S		rot mount 90	E
		+---------------+		+---------------+
		| |  ---> x     |		| |  ---> x     |
		| |		|		| |		|
	      E | v  0.37"/pix	| W	      N | v		| S
	        | y		|		| y		|
		|		|		|		|
		+---------------+		+---------------+
			N				W

Autoguider seeing
Due to charge spreading on the Loral AG CCD (the CCD resolution is 30 microns
of 0.75 arcsec) the seeing will be overestimated.  


[The filters are currently stored in a special WFC filter box together with
spare filter spacers.]

At xterm CLI interface type

>wfcmdb                     - enable access to WFC filter database (eg. set
                              telescope focus offsets)

The filters are identified by several methods.  

A WFC filter holder number written on each one for ease of identifying
when changing filters - this number has no other significance.

An ING site-wide database number not directly used by the WFC software but
stored in the WFC filter database.

A unique 5 bit code on each filter holder - see below.

A name translation of the 5 bit code eg.  R, U etc...

A filter position number on the filter wheel eg. 1,2.....6

If simply altering a known filter offset follow the interactive gui and
"commit" the changes to the database and "save" on exit.

After exiting from gui type

>cmd MCA RESET              - to update the volatile use of the database
                              and enable the changes.

If changing a filter to another known filter see the section on use of 
GANTRY terminal.

To install a new filter (in a unique filter holder) you have to "read" the 
filter holder 5 bit code on the edge of the filter holder.

         inside edge  |   Bits 0  through  5     |  outside edge

where a set bit is a raised part of metal and the least significant bit
is to the left.

For example: the OIII filter has code  1 0 1 1 0 = 13

Update the WFC database using the >wfcmdb and >cmd MCA RESET commands.


The HST guide star catalogue to V of approximately 15.5 magnitude is
stored on /catalogs/hstguide.sun .  This 300 Mbyte file contains the complete
GSC catalogue and can be efficiently searched for guide stars for the WFC.

To run the software the following environment variables and alias have to
be set up in an observing system xterm window on LPSS13 or on the TO
window (these are automatically setup by startobssys but if you want to
run it from some other window then type

>setenv GSC_DATA /catalogs/hstguide.sun     - pointer to the HST catalogue 
>alias gsc_apm '/home/mike/soft/wfc/gsc_apm' - the latest version with 6+Nom
                                               beamswitch options
The program can either be invoked using command line options such as:

>gsc_apm RaDec="10 30 0 -1 0 0" Rotpos=180 Equinox=J2000 Beam=N (Nom pointing)
>gsc_apm Rotpos=90 Equinox=B1950 RaDec="21 30 11.3 12 10" Beam=C (CCD#3 centre)

or run interactively viz:

 Command lines arguments are:
 RaDec="hh mm ss dd mm ss"
 RotPos=angle (180 default)
 Equinox=J2000 (or B1950)
 Beamswitch=N (or A,B,C,D,E,F)
	(A=centre of CCD#1, B=centre of CCD#2, 
	 C=centre of CCD#3, D=centre of CCD#4
	 E=centre of Autoguider
	 F=rotator centre, located on CCD#4)

 Example command lines:
   gsc_apm RaDec="10 30 0 -1 0 0" Rotpos=180 Equinox=J2000 Beam=A
   gsc_apm Rotpos=90 Equinox=B1950 RaDec="21 30 11.3 12 10" Beam=N
 Ok...... do it interactively then.......
Rotator angle [180?]
Do you want to impose magnitude cut ? [N]
Do you want to precess input coordinates to J2000 ? [N]
 Field Centre:(h,m,s,d,m,s)
12 0 0 0 0 0
File: gsc.out already exists - clobber ? [Y]
 Catalogue Ra limits =  8963072  9001638
 Possible guide stars (also listed in gsc.out)
 Catalogue no.     Ra           Dec       Magn  Guide X  Guide Y
  49320270   11 59 44.965  - 0 25 11.57   13.6  1512.7    20.1
  49320404   11 59 48.562  - 0 21 11.56   14.6  1367.0   668.0
  49320532   11 59 56.012  - 0 19 22.73   15.2  1065.4   961.7
  49390619   12  0  0.230  - 0 19 21.36   12.6   894.7   965.4
  49390146   12  0 18.344  - 0 23 41.42   15.2   161.2   263.4
 Total no. catalogue stars read in =  161
Do you want plot E-W direction reversed ? [N]
Do you want to alter default line width ? [N]
 Graphics device/type (? to see list, default /NULL): 
Do you want another plot ? [N]


The catalogue information is also written to gsc.out in the current directory.
A plot of a 1x1 degree field with the layout of the science and autoguider
CCDs superposed is optionally available + 100% (solid) and 50% (dashed)
vignetting circles superposed.


The observing log is actually stored in /int/etc and called something like
19970525.INT .  For printing out your own version copy to a suitable
directory, edit out any crap and put in any comments and then use

>a2ps -1 19970525.MINE >

if you want a readable printed copy.


For changing filters or rotating top end for cryostat fill, which should
be done at rotator position of 180 or testing shutter etc..

Check RS232 cable is connected to top socket on gantry rail.

If console does not respond check communication is set for 8 bits no parity
by pressing "PF3" and then using cursor keys to select COMMS option and "enter
key to scroll through options for 8 bit no parity.  After setting COMMS press
"PF3" to go back to terminal mode.  

Hit  a couple of times to get observing system login prompt.

Login as observer, using standard password.


> obssys                - sets up commands etc..

To change a particular filter

GANTRY> change R        - filter name or number, eg. R, 3

....wait for action to prompt.....
....turn the black knurled knob on filter access hatch to open it....
....remove filter and change for new one....
....turn black kbob back to close the hatch which is then locked automatically

To rotate PF top-end

GANTRY> rotate sky 180  - rotate PF top end to 180 degrees

To test shutter

GANTRY> wfcshutter open
GANTRY> wfcshutter close

Logout when finished

GANTRY> logout


SLOW(STANDARD) are the readout speeds = total readout time of 168s(155s)
for all 4 science devices.  Full well on all devices is 200,000e-

At SLOW(STANDARD) the gain and readout noise for the active devices are:

        CCD      Gain e-/ADU     Readout noise e-     Max ADU <+/- 2% linearity

        #1         3.2 (3.4)       7.4 (6.0)          55,000 (54,000)
        #2         3.2 (3.4)       6.4 (7.4)          57,000 (51,000)
        #3         2.9 (3.0)       7.7 (7.0)          57,000 (56,000)
        #4         3.3 (3.5)      10.2 (9.0)          56,000 (50,000)

The CCD broadband zero-points (ie. that magnitude that gives 1 detected 
photon/s) are:

        CCD        U      B      V      R      I      Z

        #1        23.8   25.6   25.7   25.6   24.9
        #2        23.8   25.6   25.6   25.6   25.0
        #3        23.6   25.6   25.6   25.6   25.0
        #4        23.6   25.6   25.7   25.6   25.0

Note. U suffering from replaced 3rd corrector element which is not optimally
      coated - probably loses 0.2 mags.

#1  Suffers from horizontal streaking from very bright stars and has shadow
    of radiation shiled in bottom right hand edge
#2  Slight vignetting at top right
#3  Vignetted in bottom left corner
#4 "Shadow" of support screw in middle 

Active area 2048x4100 pixels, overscan regions give 2148x4128 pixels on 
readout.  Nominal 15 micron pixels (needs astrometric check) gives active
area of 30.72x30.72mm or 12.6x12.6 arcmin per CCD.

      Trimsec [51:2098,1:4100]
      Biassec [1:50,1;4128]

#5    Autoguider CCD with outer half masked for frame transfer.        

Capstan settings viewed with rotator at 180 deg


                |                                        |
                |                                        |
                |     7.90mm                             |
                |                                        |
                |                                        |
                |                                        |
                |                                        |
                |                                        |
                |                                        |
                |                             7.73mm     |
                |                                        |
                |                                        |
                |                                        |
                |                                        |
                |                                        |
                |                                        |
                |     7.15mm                             |
                |                                        |
                |                                        |



In iraf (defined in 

use wfc_patch6 to create a mosaiced image of the 4 CCD's in one frame -
so in /obsdata/intb/19980525 for example 

	wfc_patch6 r102783

would generate the image