You will be using the ST-8 camera either as an imaging camera, or as the detector for the Optomechanics 10C Spectrograph. In both cases, set up and operation of the CCD camera are identical.
You will be using the ST-1001E as an imaging camera.
This manual is designed to take you through the setup and operation of the CCD cameras step-by-step so that you can perform your laboratory without having to rely heavily on a Teaching Assistant. The CCD is delicate, however, so if you are uncertain about how to do something please ask the T.A. for help before trying to do it yourself.
Throughout this manual, it is assumed that you already have a general understanding of the use of CCD cameras. Appended to the end of this manual is a list of references to literature on the design and use of CCDs if you need additional information not provided here.
When you arrive at McCormick Observatory, the CCD (or spectrograph) mounting will already be connected to the tail end of the 26'' refractor. If it is not, only the T.A. is authorized to change the tailpiece. Do not attempt to do this on your own.
With the tailpiece mounted on the telescope, and the CCD mounted to the tailpiece, set up is actually quite simple. The CCD needs to be connected to the control computer (an IBM compatible PC), which requires the following steps:
A PC is required to control the CCD's various functions. There are two different software packages installed on the PC which can control the CCD, CCDOPS and SkyPro. Both programs are essentially the same, the main difference being CCDOPS is run from DOS and SkyPro is run from Windows. The following sections of the manual are written assuming that you will be using CCDOPS to control the CCD. However, SkyPro is very similar to CCDOPS, and if you prefer to use the Windows environment, you can use SkyPro.
To start CCDOPS do the following:
You should now see the CCDOPS software displayed on the monitor. The next section will describe how to control the camera with this software.
This section of the manual covers the initialization, use, and shutdown of the CCD camera with the CCDOPS software. If you are using the SkyPro package, the steps are similar, however, location of the commands may not be in the same menus as in CCDOPS.
CCDOPS is DOS-based software, so to maneuver through the menus you will use the arrow keys. To select a menu item, press return when you have highlighted it. You can also use the mouse to select menu items as you would in Windows.
Prior to observing, there are several steps you should take to initialize the CCD Camera. First, you need to establish communication from the CCD head to the computer. To do this, simply select Establish COM link in the Camera menu. When the program is started, it includes a status area on the bottom of the screen. In the camera section of the status area it should say ``Link:Not Found'' when you start CCDOPS. After selecting Establish COM link, however, this should change to indicate that a link has been established through port LPT1 to the ST-8. Once this link has been established, you can begin using the CCD Camera.
Next, you should choose Setup from the Camera menu to set the CCD operating temperature, resolution, and dark frame use. To minimize dark current, you want the CCD temperature to be as low as possible. The CCD has an on-board thermoelectric cooler which can quickly cool the chip to low temperature. After choosing Setup in the Camera menu, type in a setpoint where indicated. This value should be between 0 and -10 Celsius. Once you've entered the setpoint, switch the temperature regulation to active. The current temperature is displayed at the bottom of the CCDOPS screen. You can begin exposing the CCD when the temperature nears your setpoint (should be within a few minutes).
In the same Setup box, you can also choose the resolution of the camera. There are three resolution levels, High, Medium, or Low. In high resolution mode, the chip reads out all pixels. In medium, the chip reads out bins of 2x2 pixels, and in low, the chip reads out bins of 3x3 pixels. High resolution mode is best, since you keep the most information when you read all pixels. The drawback to high resolution is that the chip read time is significantly longer than in medium or low resolution mode. Therefore, use high resolution on program objects, and use medium or low on focus frames, first test frames of program objects, and other throwaway exposures.
Finally, you can select whether or not you would like to take dark frames. Since this CCD is only thermoelectrically cooled to just below 0 Celsius, it has a significant amount of dark current. Subtracting a dark frame and from your real exposure will remove fixed pattern noise from the variable dark current and bias level of the chip. CCDOPS can be set to automatically take and subtract a dark frame from your real frame before displaying. To do this, set dark frame to Also in the Setup window. If you will be taking multiple exposures of the same duration and at the same temperature then you can also set Reuse Darks to Yes. Note that a dark frame must be the same length as your program frame. Therefore, a 15 min. exposure with a dark frame will take more than 30 minutes including readout time. The reuse dark option will significantly reduce observing time for multiple long exposures.
Note that the CCD Camera Setup can be changed at any time during the night. You can switch resolution, dark frame use, and temperature (although there is really no need to change the temperature) whenever you wish.
Using the ST-8 CCD with the CCDOPS software is quite easy. While the software has many sophisticated options, you can obtain high quality exposures very simply. There is no cookbook list of numbered steps you can follow, since how you use the camera will depend very much on the observing program you are performing. However, there are several steps common to all programs which will be outlined below.
The most important thing to do before beginning your observations is to focus the telescope as best you can. To do this, select the Focus command in the Camera menu. The Focus command tells the CCD to take a series of frames continuously, allowing you to adjust the focus of the telescope in between each one. Of course, to focus the telescope, you need to have an object to focus on, so before beginning to expose the chip, point the 26'' at a fairly bright star (say 9 to 12 magnitude). In the Focus window, set the CCD to ``Planet'' mode. Then set the exposure delay to give you enough time to adjust the telescope focus between exposures (for the 26'', you will probably need at least 20-30 seconds). Finally, set the exposure time for each frame long enough to integrate over changes in seeing, ten seconds or so is enough for a bright star. When you hit enter, the CCD Camera will begin a sequence of exposures. Planet mode tells the camera to first take a full frame exposure. Then, after reading this exposure out and displaying it to the screen, you will see a white box appear in your image which is smaller than the chip. You can place this white box anywhere in the image using the arrow keys. After putting the box around the star you are using to focus, hit the return key twice. This will instruct the chip to only read out the portion of the chip included in the box. Chip readout times will therefore be reduced and you can focus the telescope quickly. Once you have used the ``locate'' box to select your focus object, crank the focus of the 26'' 1-2 cranks between focus exposures. If for some reason you lose the star from the ``locate'' box, you can restart Planet mode without exiting your current Focus run. To do this, simply select Planet from the menu which appears in the upper left hand corner when a focus image is displayed. This will make your next frame full size again so you can recenter your focus star.
There is a straightforward method for determining the focus of the telescope quite accurately. Begin your Focus exposure set with the telescope way out of focus in one direction. As the frames progress, slowly move the focus in or out so the stellar image begins to narrow on the chip. To find the focus, continue doing this until you've gone past the focal point, and the stellar image has begun to widen again. Once you're sure you are past the focal point, simply go back in the other direction until you have the image as narrow as possible. To further improve the accuracy, you can use the peak pixel value of the image. The number which is displayed to the left of the image window gives you the value of the pixel in the displayed frame which has registered the most counts. As you achieve better and better focus, the light from a star is concentrated into a smaller area. Therefore, the value of the central pixel will increase as you achieve better focus. So, while you are focusing the stellar image and minimizing its spatial extent, look for the maximum pixel value. When the image is at its narrowest, and the pixel value is at its highest, you have achieved focus.
After achieving focus, the use of the CCD Camera will depend on your particular observing program. The rest of this section will describe how to take a standard CCD exposure, which is common to all programs. To take an exposure, select the Grab command from the Camera menu. The Grab command is very similar to the Focus command, except it takes only 1 exposure instead of a series. Simply select your integration time, and press Return and the exposure will begin. Remember, the resolution (high, medium or low) and use of dark frames for this exposure is set in the Setup option of the Camera menu. You can change those options between each exposure to fit your observing needs.
In some cases, you may wish to use SBIG's ``Track and Accumulate'' software as an alternative to simply using the Grab command. To use this option, select Track and Accumulate under the Track menu in CCDOPS. The Track and Accumulate option allows you to take several shorter exposures of your program object rather than one long exposure. The software will then co-register and co-add the multiple short exposures, leaving you with a single, stacked image. Using this software option will require you to set the following parameters:
The other parameters for Track and Accumulate can be left with their default values.
After you begin the Track and Accumulate process, the first exposure will begin. Like the Focus command in ``Planet'' mode, your image will be displayed with the ``locate'' box displayed. You now need to move the locate box until it encloses a star which can be used for guiding. After subsequent exposures, the software will use the pixel position offset for your chosen guide star to perform the co-registration. For this reason, you should select a fairly bright star away from the edges of the chip as your guide star.
When you are finished with your observing program, you will need to shutdown the CCD and computer system. First, select Shutdown from the Camera menu. This terminates the communications link from the CCD to the computer. Next, select Exit from the File menu. This will return you to the DOS prompt. You can now turn the PC off by pressing the Power button. Now simply perform the setup in reverse. Remove the power cable from the CCD head and roll it up. Remove the ribbon cable from the CCD head and roll it up. Unplug all plugs and store them on the cart as you found them when you arrived. Roll the cart slowly into the observer's room for storage.
As mentioned above, CCDOPS contains many more options than those described in this manual. You will probably not need to use any of them other than those described above, however. If you are performing a lab which does require some other option, either the TA or the lab manual will describe how to use it. This last section will go over a few final details about using CCDOPS.
At any time, hitting the Esc key on the keyboard exits what you are doing. So when you are finished with your focus run, or if you want to abort a long exposure because of a problem with the telescope, etc., simply hit Esc. Also, after your exposure taken with Grab has finished and has been displayed to the screen, Esc gets you back to the main CCDOPS screen. The current image is kept in the image buffer until it is saved to disk or another exposure is taken. So after your image has been displayed and you have hit Esc, you can continue to redisplay it until you save the image or replace it with a new one. To redisplay it, select Image from the Display menu. This option also allows you to change the display parameters so that you can enhance faint detail or only display the brightest portions of the image. To change the display parameters, simply type in a new background and range where indicated in the Image window.
In addition to changing the display parameters with Image, you can also get some useful information about your image. Set the ``Display Mode'' in the Image window to ``Analysis'' after you have selected Image from the Display menu. You will notice a menu of options now available in the upper left hand corner of the display. If you select ``X-hairs'' (or simply type X), a set of crosshairs will appear on the display. The box in the upper left hand corner will now display the pixel position and value for the current pixel.
Finally, you will want to save your images to disk so that you can retrieve them later for data reduction and analysis. If you will be porting the images to the department's UNIX Workstations for analysis in IRAF or IDL, you will want to save your images in the FITS (Flexible Image Transport System) format. To do this, simply select Save in the File menu. Type in a unique name for your image and then set the ``Type'' to FITS. A second window will appear, titled ``Save FITS Image''. In this window, set ``Bits per pixel'' to 16, and type in any comments you would like in the fields indicated (Telescope, Observer, Object, Comments). When you hit Return, the current image will be saved to disk.
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