The "slow" readout mode should always be used for INGRID. This can be
invoked with:
SYS> rspeed ingrid slow
(The fast readout mode can sometimes cause a problem with the
camera server and is not recommended.)
Note that the detector cannot
be binned.
Readout modes
When performing science observations with INGRID, one must select an
appropriate readout mode. The default and most straightforward mode,
correlated double sampling (CDS), can be selected with the command:
SYS> rmode ingrid mndr 1 1
When taking exposures in this mode: (a) the array is reset, (b) a
pre-read is taken, then (c) a post-read is taken at the end of
the integration. The pre- and post-reads are stored in extensions [1]
and [2] respectively of the fits files rxxxxxx.fit.
One can change the command to:
SYS> rmode ingrid mndr <Nr> 1
to invoke an MNDR (multiple non-destructive reads) mode, where <Nr>
is the number of reads. This means that <Nr> pre-reads
and <Nr> post-reads are performed. The
pre-reads are averaged and written to extension [1] and similarly the
average of the post-reads are output to extension [2]. The purpose of
this mode is to reduce the readout noise, which decreases with the
square root of the number of reads. This mode should only be used for
observations with very low backgrounds where the readout noise becomes
dominant. Normally we recommend the use of <Nr>=1.
When performing infrared imaging, one is restricted to short exposure
times to avoid saturation from the sky background. This leads to
the creation of large numbers of fits files and increases the observing
overheads
due to the time it takes to write to disk. For this reason, there
exists
the option to average a number of exposures before writing to an output
file. After all the exposures are taken, the pre-reads and post-reads
are separately averaged; the averaged pre- and post-reads are then
written to disk as rxxxxxx.fit[1] and rxxxxxx.fit[2] respectively. This
mode can be invoked with the command:
SYS> rmode ingrid mndr <Nr> <N coav>
where <N coav> corresponds to the number of
exposures to be averaged.
Here is an example to illustrate the most general case:
SYS> rmode ingrid mndr 3 5 SYS> run ingrid 10
In this instance:
3 pre-reads are taken, averaged, and temporarily stored.
3 post-reads are taken, after a delay of 10s, averaged, and temporarily
stored.
This process is repeated 5 times.
The 5 separate 'averaged
pre-reads' are themselves averaged and written to rxxxxxx.fit[1].
The 5 separate 'averaged post-reads' are themselves averaged and
written to rxxxxxx.fit[2].
Note that the total exposure time is 50s, ie. 10s x 5.
After setting <N coav> to values greater than
one,
you must remember to set the value back to one if you want to take
quick glances!
For more details on the readout of INGRID see here.
Movie mode
It is possible to use INGRID like a TV camera, by continuously reading
out the detector and displaying the images on the real time display.
One possible application for this is when you are preparing to take sky
flats and you want to monitor whether the sky is dark enough to
proceed. To set this up, type:
SYS> multglance ingrid <N> <exp time> & This will produce a sequence of <N>
exposures of
<exp time> seconds. For example:
SYS> multglance ingrid 999 2 &
Once you have finished with
the movie mode you can either press control-C or type:
SYS> abort ingrid
To optimise INGRID's performance as a "TV camera" it is recommended to
first revert to the standard readout mode:
SYS> rmode ingrid mndr 1 1
Storage modes
A number of storage modes are available for INGRID, and are discussed
in more detail here.
However, as both the current INGRID
RTD (real time display) and the INGRID
quick look package only support the "normal" storage mode, it is
generally recommend to always use this. With the "normal" mode, the
pre-read is put into the first extension of the fits file
(i.e. rxxxxxx.fit[1]) and the post-read into the second extension (i.e.
rxxxxxx.fit[2]). It can be invoked with:
SYS> storemode ingrid normal
Note that INGRID differs from LIRIS
in this respect, as in the latter case the "diff"
storage mode is generally preferred.
Windowing
By default, the whole of the INGRID chip will be read out. It is
possible, however, to define up to four readout
windows, although this is discouraged because it is not compatible
with the INGRID quick look package.
