The Astrovid 2000 CCD video camera was purchased in early 1999 from Adirondack Video Astronomy (www.astrovid.com). Its primary intended purpose is as the detector for the speckle interferometry system, but its light weight and simple controls also make it ideal for establishing a quick and direct video feed from the telescope. Note, however, that the video camera should not be thought of as an integrating device since the maximum exposure time is 1/60th of a second. The Astrovid is best applied to the viewing of bright objects (the moon, planets, bright stars) in real time, and the recording of high frequency phenomena (like speckles and seeing motion). An integrating CCD like the SBIG ST-8 is better for faint objects. The Astrovid camera is designed for use with a standard 1.25" eyepiece mount. An adapter has been constructed for the McCormick 26-inch refractor on the side of the flip-mirror system at the end of the tailpiece. A small portion of the total eyepiece field of view can be imaged with the Astrovid camera by moving the tailpiece flip mirror to its secondary position. The video output can either be directed to the high-resolution monitor soon to be located in the dome room or directly into the McCormick laptop PC for the purpose of frame-grabbing.
The following manual explains how to set up the camera, use its controls to obtain an optimal image, direct it's video feed to the desired output device, and capture digital images in TIFF format for later analysis.
General information about the camera and detector are summarized below. Note that the CCD in the Astrovid 2000 camera does not have square pixels.
|CCD||Sony HAD ICX038DLA|
|Chip Size||7.95 mm 6.45 mm|
|Pixels||811 (horiz) 508 (vert)|
|Pixel Size||8.4 m (horiz) 9.8 m (vert)|
|Power Supply||12 V DC|
|Operating Temp||20 C to 55 C|
The Astrovid 2000 CCD camera should have been mounted by the TA or the Observatory staff in preparation for your lab. If it is not, use care in following these directions.
On the side of the McCormick 26" tailpiece, there is a mount with a threaded nut that accepts a roughly 1-5/8" diameter threaded cylinder. This was designed to accept the SBIG ST-8 CCD camera. The speckle system and Astrovid 2000 mount have been designed to fit this mounting point as well.
The 1.25" mount for the Astrovid is a 2"-long brass cylinder with threading at one end and a slit cut lengthwise through the other. This slit allows the camera barrel to be locked into place with the aid of an aluminum ring clamp that fits around the mounting barrel. There is an aluminum protector ring that fits over the threading when the mount is not is use; this acts to keep the threads from becoming damaged.
To mount the camera to the tailpiece, first remove the thread protector ring from the brass cylindrical mount. Next, align the threading with the mount extending from the tailpiece and lock it in place with the threaded nut. Slide the camera barrel in and tighten the aluminum ring clamp firmly about the barrel mount. This is accomplished by sliding the ring as far toward the camera as is possible and tightening the thumb screw; the thumb screw should be aligned roughly from either lengthwise cut in the mount. Make sure that the camera is oriented so that it is perpendicular to the underside of the tailpiece. Refer to Figure 1. Note that the support brace seen in the images is not used with the video camera.
The control box has a roughly 6-foot cable that acts as a communication line to the camera itself. The box can be temporarily attached to the back end of the telescope during operation. Once the camera is in place, the two connectors at the end of this communication/video cable should be inserted into the appropriate jacks in the back of the camera. There is a BNC connector (refer to Figure 2 on the control box to which a coaxial cable can be attached. This is the video output, which can be directed to a monitor or computer.
Once all of the above steps are complete, the power line may be attached. At the present time, there are no free outlets on the power strip attached to the 26-inch telescope. There is, however, a white 12-Volt adapter attached which is not necessary for the use of the Astrovid camera. This can be unplugged and temporarily belayed. Since there are several free-hanging cables and the extra power supply is somewhat heavy, one should be careful to avoid getting hit by freely swinging objects. The black 12-Volt adapter that comes with the camera should be plugged in to the now-empty spot on the power strip and the other end connected to the control box. A red light on the camera itself will now be illuminated.
At the time this manual is being written, the camera control box and power supply are not attached to the telescope and must be connected and removed each time the system is set up. In the near future, however, a very long communication/video cable will be run from the tailpiece up the telescope tube to the axes of rotation, and then down to the main telescope control panel. The control box and power connector will be located on the pier for easier use. When this layout is implemented, setting up the video system will simply involve attaching the camera to the tailpiece, connecting the free-hanging cables, and turning on a display device.
Once the camera is in place, the tailpiece position must be adjusted to move the CCD into the focal plane of the objective. Using the crank found on the pier, rotate the tailpiece adjustment bolt until the tailpiece position indicator is aligned with the marker labeled ``speckle camera''. See Figure 3. This will bring the camera into rough focus. More refined focusing with the video camera is relatively easy because of the fast readout. The ideal focus may be checked by frame-grabbing images of unsaturated stars and checking the point spread function (e.g., with the MIRA software).
There are two possible video output devices: a TV monitor and/or PC. At the current time, the only monitor available is a large television that is kept in the observer's room and must be carried into the dome room. In the near future, a high resolution monitor will be acquired and most likely mounted on the pier in the dome room; this will make set-up very simple.
To use the television as an output device, one simply needs to attach the f-type connector on the coaxial cable to the ``ANTENNA'' port of the TV.
To use the McCormick laptop PC as a display device, first make sure that the ``Videoport Professional'' PC card is inserted into one of the two PC slots on the side of the computer. There is a connector that plugs directly into this and at the other end accepts an RCA plug. An RCA-to-F-type male connection adapter should be attached to the RCA connector. To this adapter should be attached a small female-to-female F-type connection adapter. The coaxial cable from the camera control box can be attached to this. Use of the frame-grabbing software for viewing and capturing the video output is discussed in a subsequent section.
When the new high resolution monitor and long communication cable are in place in the dome room, the monitor will be set up semi-permanently to receive video feed in the following manner. The control box will live on the pier and the coaxial video feed will be attached to a ``T'' splitter which will also be attached to the pier. One of the two outputs from this splitter will be attached to the monitor so that all one needs to do to view the camera output is attach the camera to the tailpiece, turn on the power, and turn on the monitor. The other output from the splitter will have a free cable which can be attached to the PC card in the laptop if desired. In this way, the monitor can be used for easy viewing while the laptop can be used for frame grabbing.
The Astrovid 2000 system consists of a control box, power adapter, video cabling, and the camera itself. In this section we will concentrate on the control box.
There are 3 controls that can be adjusted to help produce an optimal image.
The goal is to adjust the various controls in such a way as to produce an image with the best signal-to-noise, contrast, and dynamic range for your application. Increasing the gain results in an amplification of the signal in all pixels: in addition to amplifying the pixels of interest, the overall noise in the image is also amplified. When possible, it is preferable to produce a brighter image by decreasing the shutter speed rather than increasing the gain. The result will be a cleaner image.
The following is a summary of the various possible control settings:
Getting the desired object centered in the video camera CCD can unfortunately be a bit challenging. Since the chip is small, it sees only a small fraction of the total field visible in the eyepiece. The CCD field of view is, however, fairly well centered in the eyepiece field of view. To get the object of interest to appear on the display device, first find it by eye using the eyepiece. Get it centered as much as possible in the field of view. Now move the flip mirror on the tailpiece to redirect the light into the camera. If the object does not appear on the monitor, try adjusting the gain and exposure time. If it still does not appear, you may have to make some small adjustments to the pointing of the telescope to move that section of the image onto the chip.
To capture digital images from the Astrovid 2000, first connect the coaxial cable to the sequence of adapters that lead to the PC card in the laptop computer. Run the program called ``Image Wizard''.
From the ``File'' menu, select ``Scan...''. Alternatively, there is a shortcut button in the lower left corner of the control panel that issues the same command. Select ``Acquire'' from the box that pops up. You should now see a window which looks something like that shown in Figure 4. Make sure that ``Greyscale'' is selected in the ``Picture'' box and that ``1/1'' is selected in the ``Size'' box. You should see the live video output from the camera in the preview box. Note that the capture rate through the PC vie ``Acquire'' is not as fast as the live video rate seen through the monitor (i.e. the PC does not show every integration frame). When you're ready to capture an image, click on the ``Capture'' button and then on ``Ok''. The image you've just captured should appear in the main window of the program. Repeat this process to capture further images.
Be conscious of the number of open windows on the desktop. Capturing too many images without saving may result in memory problems. Desirable images should be saved to disk periodically and their windows should be closed unless they are needed for reference. Images should be saved in TIFF format. Most image analysis and manipulation programs can read TIFF images. Also be conscious of the amount of available hard drive space on the laptop. Data should be saved on the laptop only temporarily. It is preferable to transfer image data to another disk when possible.
You may want to capture and co-add a series of images. Note that the rate of image capture is dependent on the bus transfer rate and processor speed of the computer, but each captured frame is of the integration length selected on the control box. To co-add a series of captured images, select ``Averaged Capture...'' from the ``Video Capture'' line in the ``File'' menu. See Figure 5. You should see a window similar to that in Figure 6. You can specify the number of frames to be captured as well as the division factor. If you want to simply accumulate frames without averaging, you would leave the ``Divide Result by: '' box set to one. For complete averaging, both boxes should contain the same number.
Please leave the Astrovid 2000 and the telescope as you found them. If the camera was installed when you arrived at the telescope, then leave is installed. At the end of the night, be sure to shut off the TV monitor and/or laptop. Disconnect the power to the video camera, but leave it attached to the tailpiece. Either a TA or the Observatory staff will remove it when necessary.
If you installed the Astrovid camera system, please uninstall and store the camera in the equipment cabinet where you find it.
Finally, re-stow the telescope in the standard way.
Next: The Astronomy Library and Up: manual Previous: The OptoMechanics Model 10C