\parindent 0pt
\parskip 0.3cm
%\section{The TV Acquisition Camera} \label{ch10:tv}
\section{THE TV ACQUISITION CAMERA} \label{ch10:tv}

\subsection {Introduction and Safety}
The acquisition and guide box (A\&G) on the INT features a rotating flip 
mirror which directs the telescope beam to a high-gain Westinghouse TV camera,
thus providing field or slit viewing at the Cassegrain Focus; there is {\bf no}
camera at Prime. The Westinghouse is a high (3000) gain 
video camera with a Grinnell digital integrating store. It is a very sensitive 
system and care must be taken in its use. There is an identical Westinghouse
camera on the finder which can be directed to the Grinnell when wanted. This 
section is intended as a guide to the safe use of the TV Cameras, and how to
get the most out of their facilities.

\medskip
\mbox{}\hrulefill\mbox{}
\begin{center}
\medskip
{\bf \large The very high-gain TV cameras can be quickly and }\\
\vspace{2mm}
{\bf \Large PERMANENTLY DAMAGED BY OVER-ILLUMINATION }\\
\vspace{2mm}
{\bf \large by BRIGHT stars or BRIGHT lights}.\\
\end{center}
Do not, therefore, operate the TV until you have read all of 
this Section and preferably have also been shown how to use it. 
If you suspect overillumination you should immediately press the 
\button{FREEZE} button and turn the gain down.

\mbox{}\hrulefill\mbox{}

Some simple {\bf precautions} to ensure a long life for the TV Camera:
\begin{enumerate}
\item Check that all dome lights, including torches, are turned off
 before turning on the camera. 

\item Always view a field in {\bf DIRECT} mode first, NEVER in {\bf AVERAGE} 
      or {\bf SUM}.

\item Turn the gain up SLOWLY. The system time constant is about 3 seconds.

\item Never do a long integration with a bright star in the field.

\item Always turn the camera gain off BEFORE MOVING the telescope. 

\item DO NOT TWIDDLE knobs at random. 

\item If in doubt, press the \button{FREEZE} button and turn the gain down. 
\end{enumerate}

\subsection {Camera Control}
\label{ch10:tvc} 
The controls for the two Westinghouse TV's , Cassegrain and Finder 
are located in Bay 4, Rack 1 directly beneath 
the small TV monitors at the top which all act as raw video displays. The
Grinnell monitor itself is located directly underneath the monitors 
in Bay 4, Rack 2. Its picture can also be routed to a
monitor in Bay 1. The selector switches which allow TV pictures from 
all focal stations and the finder to be sent to the monitor are located 
directly below, alongside an array of feature-selection buttons which 
are described in more detail further on. The final piece of 
hardware in the TV system is a joystick controller box which normally 
resides on the telescope Control Desk.
Figure \ref{ch10:fig1} shows the location of the TV camera controls on the
INT Control Desk (bay 4).

Control of the flipmirror as part of the A\&G box is made through both 
the ADAM instrument control software environment and the telescope
User Interface, from which Guide and TV probe move requests
can be made. The TV flip mirror should be in place when it is
necessary to view a new field or when ready to guide. Note the possibility
to use colour filters with the camera: the
finder filters numbered 1, 2, 3 and 4 are respectively CLEAR, B, V and R.

\begin{figure}[ht]
\vspace{7.5cm}
\caption {TV Acquisition Camera controls}
\label{ch10:fig1}
\end{figure}
 
The Grinnell Camera is controlled with several groups of switches and push 
buttons: A group of three rotary switches serve to define the setup of
image integration and contrast. The main Grinnell functions are controlled
with a 3$\times$3 block of buttons just above the rotatary switches. 
Note the facilities to archive the camera image and to obtain a hard copy.
A further set of push buttons serve to select functions from a menu which 
enable on-line image analysis.

The three rotary switches below the panel buttons act as follows:
\begin{itemize} 
\item {\bf INTEGRATION } 

The absolute position of this switch determines
the number of frames of integration N=2$^n$.
\item {\bf BACKGROUND}

Makes the background blacker or whiter. There is 
no absolute position, the effect is determined
by the direction and number of steps moved. However, after a complete 
\button{RESET} of the TV control System, the background always has the 
value 2048.
\item {\bf CONTRAST} 

As for the BACKGROUND switch but it controls the
contrast {\it i.e.\/} softens or enhances.
\end{itemize}
 
The main 3$\times$3 block of the main Grinnell controls have the following 
functions, from top to bottom and left to right:

\begin{itemize}
\item {\bf AVERAGE} 

Recursively filters on-target integrations to increase signal-to-noise ratio. 
The number of on-target integrations (N=2$^n$) are selected by the 
{\bf INTEGRATION} rotary switch. The filtering is done in 
the TV system microprocessor; the
image is effectively smoothed over 2$^S$ frames, where  S equals 2 or 3.
The signal-to-noise ratio is proportional to $(2^S-1)^{1/2} N^{1/2}$ and the
effective time constant is 40(2$^S$N) milliseconds.
Note that when using {\bf AVERAGE}, for a given S/N ratio
a smaller number of on-target integrations is required than with {\bf SUM},
and less charge on the cathode is accumulated.
Because {\bf AVERAGE} gives a higher S/N ratio, at the expense of
a longer effective time constant, it should be used in preference to 
{\bf SUM} except for quick looks with short integrations,
{\it e.g.} acquisition of an object just below the {\bf DIRECT} mode limit.


\item {\bf SUM}

ON-target summation of N=2$^n$ frames (each of 40 msec),
selected via the {\bf INTEGRATION} rotary switch. 
The signal-to-noise (neglecting dark current)
is proportional to N$^{1/2}$. On-target integration is potentially
dangerous because the photocathode may be damaged by excessive build-up of 
charge, so care is needed. In all but special cases {\bf AVERAGE} is to be
prefered: it is usually better to use moderate on-target integrations with
filtering rather than very long integrations.
 
\item {\bf DIRECT} 

Real time digitisation at normal frame rates. 
Normal Frame integration time is 40ms.
 
\item {\bf FILL} 

Fills in the alternate lines of a stationary ({\bf FROZEN}) 
 picture. Considerably improves the appearance of  
 faint, extended objects.  
 
\item {\bf FREEZE} 

Freezes the current picture. 
 
\item {\bf ARCHIVE} 

Saves TV frames in the memory of the 
3210 Instrument Computer. 
 
\item {\bf OVERLAY-ONE} 

Enables/disables the first graphics overlay 
 plane ({\it i.e.\/} the boundary, the orientation and the scale).
 
\item {\bf OVERLAY-TWO} 

Enables/disables the second graphics overlay 
 plane ({\it i.e.} the integration, tau, background 
 and contrast information). 
 
\item {\bf CROSS HAIR} 

This puts a crosswire on the screen.

\end{itemize}

To the left of the rotary switches are three more push 
buttons:\button{MENU}\, , \button{SELECT} and \button{RESET}\,.
Pressing \button{MENU} will freeze 
the image and cause the first of a two-page image processing Menu to be 
displayed.
% as shown in Figure \ref{ch10:fig2}. 
%\begin{figure}[t]
%\vspace{20cm}
%\caption {Grinnell 2-page menu}
%\label{ch10:fig2}
%\end{figure} 
A description of the available menu functions is given in 
Section \ref{ch10:menu} towards the end of this chapter.
A cursor will appear, which can be positioned on a selected Menu item by 
repeated
depressions of the \button{SELECT} button. Alternatively, the joystick may be 
used for the selection of a Menu function. The 
joystick controller box also contains the buttons to enable/disable the 
movement of any displayed cursor. Press the \button{ENTER} button 
on the joystick controller to enter the menu selection.
Pressing the \button {RESET} button will completely reset the system: 
all overlays {\it etc.\/} will be lost.

\subsection {Powering up the TV system}
To operate the system follow these steps: 
\begin{enumerate} 
\item Make sure all lights, including torches, are out in the dome. 
 
\item Turn on the power of the Finder (and if necessary, Cass) 
monitors in Rack 1 and 
 let them warm up so that you can see if there is any image on 
 the TV cameras. 
 
\item Ensure that the gain controls for Cass and Finder
are turned fully OFF (turned anti-clockwise until they click). 
 
\item Press the black \button{ON} button on both control boxes. The lights 
 marked DELAY and RESET will come on. Wait about 15 seconds until 
 they go out and the green ON light comes on in each case. If 
 RESET does not go out, press \button{OFF}\,, check step (3) and try again. 
 
\item Each TV control box has two scan reverse toggle switches 
 (which allow the orientation of the TV display to be changed 
 to match finding charts for example). Initially, however they 
 can be used to check the status of the system. When the monitors 
 are powered up, and adjusted in brightness to give a visible 
 background, switching the toggle switches will, if the system 
 is OK, result in the bright edge of the TV cathode traversing 
 the screen. If this is not seen then check the monitor brightness 
 settings. If there is still no response then call for help. 
 
\item To use the TV system, you will need to have:-
\begin{enumerate}
\item TV probe centred.
\item Flip Mirror viewing field or slit as desired.
\item Comparison Mirror out of the way.
\item Autoguider Probe out of the way.
\end{enumerate}
\item To remove flickering of picture and white screen at start-up 
 press \doublebutton{FINDER}{SEL'D} and then the \button{DIRECT} button. 
\item The bias has been selected to give a black picture when the 
 camera is started up otherwise the light level on the monitor 
 would be very high in a bright sky. Decrease the BACKGROUND
 control (Section \ref{ch10:tvc}) until you begin to see white noise 
on the screen. 

\end{enumerate} 
\subsection {Normal operation}
\begin{enumerate} 
\item Before viewing a source, select the \button{DIRECT} viewing mode on the 
 Grinnell buttons. 
\item When pointing at a field, even if you know that it only contains 
 18th magnitude objects, turn up the gain SLOWLY whilst observing 
 the effects on the direct (raw video) TV camera monitor. There is a
lag of about 3 seconds between operating the gain control and the
full effect being seen. 
\item As the object or field of interest appears on the direct screen 
 adjust the gain control to give a sensible picture on the 
 Grinnell monitor. 
\item If the gain control reaches maximum without ill-effects on the 
 direct screen and further gain is required, then select 
 \button{AVERAGE} mode on the Grinnell and adjust the number of frames 
 of integration ONE step at a time waiting between steps to see 
 the resultant image. When the Grinnell is in the average mode, the
 direct monitor will flash the integrated signal with a period 
 equal to the integration time. 
\item If in doubt, press the \button {FREEZE} button and turn down the gain. 
This ensures that the TV read beam is not blanked and therefore 
any over-illumination is discharged. Hitting the red \button{OFF} button
does not guarantee this and should be avoided. It is always safer to
turn the {\bf GAIN} control to its clicked-off position than to operate
the \button{OFF} button.
\item Always turn the gain off before moving the telescope. You never know
which first magnitude star is lurking round the corner!
\end{enumerate}

\subsection {The Grinnell MENU} 
\label{ch10:menu}
 
 When the menu is displayed on the Grinnell TV monitor, move the 
cursor to the function required and press the \button{ENTER} button on the 
joystick controller to process the selection; {\it nota bene\/}: the 
\button{TRACK} switch, No. 3 in the bottom row,
should always be up, {\it i.e.} ON). When the function selected requires 
further positional information, up to 4 cursors can be enabled on 
the screen depending on the function. When they appear they may well 
be overlaid and so only appear as one. On the joystick controller 
the cursor switches determine which cursor(s) the joystick will 
control at any one time (for these switches, UP is equivalent to ON). Once the 
cursors have been positioned as desired, ensure that at least switch 
\button{1} is on, and then press \button {ENTER} again to initiate the 
processing. A quick guide to the menu is given in the following sections.
\vspace{1.0cm}

{\bf Grinnell Menu Functions: Page 1}

\begin{itemize}
\leftmargin 0pt

\item {\bf DRAW RESTRICTED PROFILE} 

Requires TWO cursors to be positioned in either 
the X or Y plane and draws the profile of the 
data contained in displayed image between the 
two cursor points on Overlay Plane 2. At the 
start the cursors are overlaid. This function is 
used for seeing estimates as it gives the FWHM 
of a star image in arcsecs. The PROFILE is 
automatically erased when {\bf DIRECT} is pressed. 

\item {\bf SET FINDER ZERO POINT}

Define centre of Cassegrain or Prime field as viewed on the
finder TV.

\item {\bf GET GUIDE STAR} 

Plots on the Grinnell view of the finder field the `catchment area' for 
possible guide stars at {\bf Cass} in the form of a circle 
which represents the autoguider probe range and an 
enclosed square in which the probe can vignette the 
field. The area between the two thus represents 
the available area in which guide stars may be 
acquired. The slit is also marked.
At {\bf Prime} the catchment area is a rectangle which will rotate 
with the rotation of the prime focus assembly. 
Gives a cursor for guide star selection.

\item {\bf CALCULATE MAGNITUDE} 
Requires one cursor to be positioned over the 
object and displays the integrated magnitude of 
the object. There is an arbitrary zero point 
for the magnitude scale. 

\item {\bf MOVE STAR TO SLIT} 

Requires two cursors, one to select the star 
and
one to place on the slit or desired new position.

\item {\bf CALCULATE DISTANCE } 

Calculates the distance (x and y and total) in 
arcsecs between two cursor positions, on Overlay Plane 2.

\item{\bf INITIALISE} 

Initialises the TV system. No cursors.
Like pressing the \button{RESET} button, it resets display parameters.

\item {\bf ERASE ALPHANUMERICS} 

Clears the areas of the overlay planes used
 for 
displaying information ({\it i.e.\/} the MENU)

\item {\bf ERASE OVERLAY}

 Erases overlay plane number 2. 

\item {\bf ERASE IMAGE} 

Erases the image plane.

\item {\bf ERASE PROFILE} 

Erases Overlay Plane 2 used to display profiles.

\item {\bf NEXT PAGE.. } 

Displays the second page of the menu.
\end{itemize}
\vspace{0.3cm}
{\bf Grinnell Menu Functions: Page 2}
\begin{itemize}

\item {\bf TEST PATTERN 0, 1, 2, 3}

Displays the Grinnell test pattern. 

\item {\bf ERASE TEST PATTERNS} 

Erases a test pattern. 

\item{\bf INTEGRATION PARAMETERS} 

Displays the current integration parameters on
Overlay Plane 2 ({\it i.e.\/} the current status of the
rotary switches). 

\item {\bf DRAW SLIT } 

Requires all four cursors to be positioned 
independently and then joins them up on Overlay
Plane~1. Intended to be used for marking slits,
but can be used to draw any quadrilateral. 

\item {\bf DRAW CIRCLE} 

Requires two cursors to be positioned to define
the diameter of a circle which is then drawn 
on Overlay Plane 1. Useful for defining the 
position of photometer apertures. 

\item {\bf DRAW BOX} 

Two cursors are enabled which are used to define
the sides of a rhombus on Overlay Plane 1. The
line joining the two points must have a positive
gradient in the X-Y plane of the screen. If the 
two cursors have the same Y position, they will
define the top side of a square. If they have 
the same X position, they define the left hand
side of a square. 

\item {\bf ZOOM} 

Zoom factors are determined by the state of the
function switches {\bf FUN A} and {\bf FUN B} on the cursor 
controller. Setting one or both of these switches 
followed by \button{ENTER} causes a new zoom factor to 
become operational. The factors are: A for a factor 4, B for a factor 2,
and A+B for a zoom factor 8.
The zoomed image can be panned via the joystick.
To exit from {\bf ZOOM}, turn both function switches
off (down) and press \button{ENTER}. The facility 
requires the {\bf TRACK} switch to be up (ON).
 
\item{\bf ARCHIVE FULL IMAGE}

Creates a `.BDF' file of the currently displayed Grinnell image on the 
EGLE disk.

\item {\bf SET ROTATOR PA} 

Gives two cursors to select rotator orientation.
Use \button{ENTER} to select and exit.

\end{itemize}

\subsection{Complete restart of the TV control system}

If the TV system has been completely shut down, then check that the following
units in the Clip Centre (Bay 8) are ON. 
\begin{enumerate}
\item The large Grinnell systems unit (power
switch bottom left). 
\item
The Westinghouse camera control units below it (front switches).
\end{enumerate}
The camera control software is now held in ROM and the startup/reset procedure
consists of pressing the \button {RESET} button on the Grinnell control panel.
\vfill
\eject
