SSCCD Operating Notes
These set of notes are intended as an introductory guide for new
users of the SSCCD at the VATT. These notes are by no means complete
but should provide the reader with enough information and guidance to operate the camera.
Contents
The SSCCD is a back-illuminated 2048x2048, 24 micron pixel Tektronics CCD
which has a SpectraSource controller and is operated using SpectraSource software running on a dedicated 486-66 PC. The detector has a plate-scale of
0.33 arcsec/pixel at the VATT and provides a field of 11.26 arcmin. In addition, there is a field-flattening lens available for use with the camera but observers should be warned that the lens causes significant internal reflections and should only be used if it is absolutely necessary (i.e. for programs which require a uniform point spread function across the entire VATT field).
The SSCCD should be properly mounted and cabled prior to your run by one of the VATT engineers. The SpectraSource controller box which hangs off of the
telescope below the filter port should also be switched on and should stay
on for your entire run. Do not power this off unless you are disconnecting
the cables to the CCD. You should notice two LEDs on the northern side
of the box - a red one and a green one. The red LED is a power indicator
while the green LED is lit if the CCD is at the proper operating temperature.
The proper mounting of the SSCCD on the VATT is shown in the diagram below:
The SSCCD PC is located at the far end of the control room desk to the
right of the Guider PC. If it is off, turn it on and, after
it is done booting up, type win
at the C:\> prompt - this will launch
Microsoft Windows 3.1. In the Spectra Source folder, double-click on the icon labeled USE THIS. This launches the Spectra Source CCD software.
When the software is first started, the following message appears on the screen:
Camera Coolers have been turned on. Please wait 30 minutes for the
camera to cool.
This message can be ignored because the SSCCD is cooled by liquid nitrogen rather than by a thermo-electric cooler like the majority of SpectraSource cameras for which this software was written. Click on the OK button or press ENTER to launch the full Instrument Control window. You can click on the upwards pointing arrow in the upper-righthand corner to maximize the window.
The first thing you should do is go to the Initialize menu and select the Configure option. A new window should pop-up and the only item of interest to you and which you might need to change is the entry at the very bottom of the window labeled Image Path. This is where you can specify the directory to which your images will be saved.
The SSCCD PC is running PC-NFS and at boot-up time a connection is made to
the UltraSparc and the directory /home/vattobs is mounted as the E:\> drive on the PC. This drive has a large amount of disk-space and is the preferred storage destination for your images. As an example, if you'd like to save your images in a directory called 10dec98 in the directory /home/vattobs then you
would type E:\10dec98\ for the Image Path in the Configure window. NOTE: Do not forget the trailing slash on the directory name. Click on the OK button or press ENTER.
Next you should go to the Initialize menu and select the Reinitialize Camera option. This will reset the camera and check that communications are indeed established between the PC, the controller box and the camera in the dome. You will again get a message about the camera coolers which you can ignore and you will also get a message that the camera has been successfully reinitialized. When you are done for the night, you can leave the Spectra Source Instrument software running but, if you do so, you should reinitialize the camera following this procedure at the start of the next night.
You should also under the Analyze menu select the Coordinate Window option. This will bring up a box which will give you the X and Y position of the image cursor and also a temperature reading from the camera. When the CCD is cooled to operating temperature, the display will read somewhere between 265.0 and 268.0 "degrees". If it gets above this, the CCD is warming up and it is time to fill the dewar.
The menus which you will be concerning yourself with most of the time are:
File, View, Analyze, Expose, Scripts, and Initialize.
The options under the Multiframe menu are usually implemented in
scripts which we will discuss later and the options under the Process
menu are redundant because the images can be processed and analyzed using IRAF on the UltraSparc.
The File menu allows you to open, close and save images.
The View menu allows you to select from a variety of zoom values when displaying images on the PC. This is especially useful when trying to display large (usually full-frame) images which are much larger than the resolution of
the monitor.
In addition to the Coordinate Window option mentioned above, the other useful features of this menu are the Windowing, Measure Intensity, X-line Scan, and Y-line Scan options.
- The Windowing option allows you to select the contrast level of the image displayed on the screen. You can adjust the value by moving the scrollbar with your mouse or using the up and down arrow keys.
- The Measure Intensity option perfoms some simple image statistics on the image regions of your choice. To select the region, place your mouse at the upper left-hand corner of the image portion that you are interested in and click the left mouse button. While holding down the left mouse button, drag the mouse to draw a box around the region and then release the mouse button when you are satisfied. A window will appear with a summary of the average, median, max, min, and sum data values as well as the (x,y) coordinates of the starting point of the box and its extent in x and y.
- The X-line Scan and Y-line Scan options, as their names suggest, allow you to take image cuts along the x and y directions respectively. Just place the cursor anywhere in the appropriate row or column and click the left mouse button.
The Expose menu allows you to control the exposure time and type of exposure you wish to take. The options available under this menu are Exposure Control, Full Frame Exposure, Sub Frame Exposure, and Sub Frame Focus.
- Exposure Control: This option allows you to set the exposure time, size of the sub frame region, and binning. A menu will appear where you will be able to change the values of these parameters. In the case of the sub frame, the X and Y values that you enter are the coordinates of the upper left-hand corner of the subframe. The origin of the SSCCD image display is always in the upper left-hand corner. If you desire binning, click the Enable button in the Binning portion of the window and then enter the binning factors in the x and y directions. If you no longer require binning, just unselect the Enable option by clicking on the button again.
In addition, there are some other parameters present which you should not change. These are values for the Overscan region, the Auto-Adjust options and the High-Gain and Auto Stretch options (these should all be unselected except for the overscan).
- Full Frame Exposure: This option will clear the CCD, take an exposure with the appropriate exposure time and binning found in the Exposure Control parameters, readout the entire CCD, and display the image on the screen. Due to the limited resolution of the display, it is suggested that if you take a full frame exposure with no binning that you select a scale of 1/4 from the View menu. You can also save the image to disk by selecting the Save As option from the File menu.
- Sub Frame Exposure: This option will clear the CCD, take an exposure with the appropriate exposure time and binning found in the Exposure Control parameters, readout the specified subregion of the CCD, and display the image on the screen. You can save the image to disk by selecting the Save As option from the File menu.
- Sub Frame Focus: This option is basically the same as the Sub Frame Exposure option except that subframe exposures are repeatedly taken and siplayed until you stop them by pressing the ESC key. You cannot analyze any of the displayed images until you stop the sequence.
The options under this menu allow you to edit and/or execute scripts which you have written in the SSCCD scripting language (see the complete SSCCD manual available at the VATT for more details). A number of scripts have already been written for taking bias frames, dark frames, dawn and dusk flat field frames, and object frames and these can be found in the C:\IMAGES\ and C:\IMAGES\NEWSCR\ directories. We will discuss some examples using these scripts in the next sections.
There are five options available under this menu but the only two that you need to use are Configure and Reinitialize Camera. The options dealing with Bias, Dark, and Flat Fields should not be used and the appropriate scripts should be used to obtain these types of data.
- Configure: The only parameter which should be changed in the Configure window is the Image Path which should be set to the directory where you would like your images to be saved. In case the other options somehow become altered, their appropriate values are:
- Port Base = 0x120
- Cooler = On
- Comm Port = None
- Continuous Clear Mode Enabled = Yes
- Reinitialize Camera: This option checks that communications with the camera and the SpectraSource controller are established and resets the electronics. It should be used immediately after starting up the SSCCD control software and at the beginning of each night if you did not exit the software at the end of the previous night. Again you can ignore the message regarding the camera coolers and instead rely on the temeperature display in the Coordinate Window to gauge the temperature of the chip.
Below you will find examples of some fairly common uses of the software including explanations of some scripts.
To obtain bias frames one should use the bias.ecl script found in the C:\IMAGES\ directory. The script contains the following:
message(BIAS script: is binning and filename set correctly?);
loop(10)
{
freeimage();
clearccd();
delay(0);
fulldigitize();
save(bias);
freeimage();
}
message(BIAS script: finished);
quit();
This script takes a series of 10 bias frames (specified by the loop statement). The SSCCD software appends a running three-digit image number to the prefix defined by the save() statement - in this case bias and the frames are labeled bias000.img through bias009.img. Remember that this is MS-DOS and filenames are limited to eight characters followed by a 3 character suffix so the save() prefix can never contain more than 5 characters. To execute the script just select the Run Script option from the Script menu and select the bias.ecl script. The script will be executed and the images saved in the Image Path that you've specified.
The relevant script is located in C:\IMAGES\NEWSCR\ and is called dusk2.ecl.
message(DUSK sky: are exposure time and save file name set correctly?);
message(DUSK sky: script generates 61Mb - 7 images with runtime of 17m);
message(DUSK sky: did you remember the binning?);
loop(1)
{
freeimage();
expose(1000);
fulldigitize();
save(su1);
freeimage();
expose(3000);
fulldigitize();
save(su1);
freeimage();
expose(5000);
fulldigitize();
save(su1);
freeimage();
expose(10000);
fulldigitize();
save(su1);
freeimage();
freeimage();
expose(15000);
fulldigitize();
save(su1);
freeimage();
freeimage();
expose(20000);
fulldigitize();
save(su1);
freeimage();
freeimage();
expose(35000);
fulldigitize();
save(su1);
freeimage();
}
It is designed to take a series of seven frames ranging in exposure time from 1 second to 35 seconds (note that the exposure times in the script are entered in milliseconds) during evening twilight. The script is started once the average counts in the center of the field fall to just below 20000 ADU.
The proper way to take dusk flats is to:
- 1. Go to the Exposure Control option under the Expose menu, enter 1 second for the exposure time and select a subframe with corner (X,Y)=(896,896) and box size 256x256 and no binning.
- 2. Under the Analyze menu, set the Windowing to 10-16.
- 3. Take a Subframe Exposure and check the counts by using the Measure Intensity option in the Analyze menu.
- 4. Repeat step 3 until the measured average counts drop below 20000 ADU.
- 5. Select Run Script under the Scripts menu and execute the script C:\IMAGES\NEWSCR\dusk2.ecl.
- 6. The script takes about 20 minutes to execute. You can change filters
in between exposures while the CCD is reading out.
You can also take sky flats at dawn using a similar script but in that case you start the script once the average counts reach 6000 ADU in a 35 second exposure.
The Ultra Sparcstation, vatt, is equipped with version 2.11 of the astronomical data reduction software package IRAF. IRAFv2.11 has the capability of directly manipulating and displaying FITS images so they no longer have to first be converted to IRAF image format. In order for IRAF to recognize which files are FITS files, you must tell it which suffixes are attached to FITS files. The SSCCD software saves the images generated by scripts as [filename].img. To allow IRAF to recognize these files as being in FITS format, you must enter the following set of commands in IRAF:
cl> set imextn="oif:imh fxf:img,fts,fits,fit plf:pl qpf:qp stf:hhh,??h"
cl> flpr
Suppose you'd like to take and save an exposure using the entire CCD but binning 2x2.
The procedure to accompish this is:
- Go to the Exposure Control option under the Expose menu, enter the appropriate exposure time, click on the Enable button at the bottom of the window to enable binning and enter 2 in both boxes for the binning factor.
- Under the View menu select 1/4 Scale (otherwise the image will overlow the screen).
- Under the Expose menu select Full Frame Exposure.
- The exposure will be taken and displayed on the screen where you can play with the Windowing and use the options under the Analyze menu to study the image.
- To save the image select Save As under the File menu and enter the name under which you want the file to be saved. You can either enter the entire filename such as test.img or just the prefix and, in this case, the file will be saved as [name].fts.
- You can now go to the Sparcstation and further manipulate the image using IRAF.
The easiest way to focus the SSCCD is to take subframe exposures which include a bright focus star and save these frames to disk. You can then display the image with IRAF and use the imexam task to measure the FWHM of the stellar images. In principle, you can examine the width of the PSF's using the X-line Scan and Y-line Scan options in the SSCCD software but this is less exact than using imexam.
Last updated December 17, 1998
Robert Uglesich / rru@astro.columbia.edu