All functions of your Apogee camera are controlled by software via the host computer. The camera, when properly connected, is powered up by turning on the computer. To connect an ISA bus camera to your computer, see Installing the PC ISA-Bus Interface Card. To connect a parallel-port camera to your computer, see the Parallel Port Setup instructions. It is recommended that you read your software manual to learn more about the camera functions described below.

Turning on the Thermoelectric Cooler
In normal operation, it is intended that the thermoelectric cooler be turned on and allowed to reach as cool a temperature as possible. The typical AP7 cooler can reach between 50 and 55 degrees C. below ambient temperature; thus, if used at 25° C, a target temperature of -25° to -30° should be set in the software (see your software manual for instructions on setting the temperature). Other Apogee cameras can obtain a maximum of about 30 to 35 degrees C. below ambient. When the cooler has reached its lowest possible temperature, the software will back it off by 2 degrees and regulate there. To prevent thermal shock to the CCD, the software ramps the temperature up and down very slowly. Allow 10 to 15 minutes for the cooler to reach its maximum temperature.

Taking Exposures
Shutter times for Apogee cameras can be as short as 0.02 second and as long as 10,400 seconds. Because CCD's are so sensitive to light, when shooting in typical room lighting conditions with a camera lens, it may be difficult to take a short enough exposure without saturating the pixels; in bright daylight, this may be impossible. Use a small aperture setting and short exposure time (less than a tenth of a second) in normal room lighting with a camera lens, and use caution when attempting to take exposures out of doors in broad daylight.

In most of the software packages that control Apogee cameras there are four types of exposures that can be taken: bias frames, dark frames, light frames, and flat frames. Bias, dark, and flat frames are used to calibrate light frames.

The bias frame is a zero-length exposure taken without opening the shutter. Its purpose is to show the electronic offset, which is in every image taken with the camera. The bias offset can be subtracted from an image, but since it exists within a dark frame, the offset calibration can be considered an integral part of the dark correction step.

The dark frame shows the amount of thermal signal contributed to each image by the CCD itself. CCD's are operated at cold temperatures to avoid as much thermal contribution as possible. For proper calibration, the dark frame (see "dark frame" in your software manual or online help) should be taken with the shutter closed, but with the same exposure time and thermoelectric cooler temperature as the light frame. No shutter is completely light tight where CCD's are involved, so it is recommended that the optical system be covered during dark exposures. Subtracting a dark frame removes most of the thermal contribution, leaving only a small amount of thermal noise in the image. As a general rule, the colder the sensor, the lower the resultant thermal noise will be. A single dark frame can be used to calibrate many light frames, if the exposure lengths and cooler temperatures are identical. Combining several dark frames (see "combine images" in your software manual or online help) to produce a master dark frame is considered by many to be a better method of dark subtraction than using a single dark frame.

The light frame is a shuttered exposure, and there are two types of light frames: normal imaging frames and the so-called flat-field (or flat) frame. The flat frame is a calibration frame and it is used to reveal artifacts in the optical path. Vignetting and dust particles (on the camera window, lens, and filters) will be revealed in a flat frame, as well as the effects of pixel-to-pixel variability of the CCD in its response to light.

The flat frame is taken by exposing the camera and its optical system to a uniform light source. This can be an evenly illuminated white card placed in front of a camera lens, or it may be a large screen held in front of a telescope tube. Astronomers sometimes use the twilight sky as a light source for flat frames, hence the name "twilight flats." The Hubble Space Telescope has been known to use uniform areas of the earth's oceans for flat frames (occasionally corrupted by intruding ships). The flat frame should be dark-subtracted and normalized (usually done automatically by the software) and then divided into each normal light image (see "flat frame" or "calibration" in your software manual). A flat frame need not be of the same exposure length as normal image frames, but the pixel values in the flat frames should be about halfway to saturation in order to ensure a good signal-to-noise ratio for the flat frame. If the pixel values are too low or too high in the flat frame, the flat field calibration will not improve the quality of the image, and, in some cases, may make the image worse. Like dark frames, a single flat frame can be reused to calibrate many images, as long as the optical artifacts (dust particles, vignetting, etc.) stay the same. A number of individual flat frames may also be combined to create a master flat frame for calibration. The primary requirement of a flat frame is that it should be taken through the optical system exactly the same way as the light frames. If the camera is rotated about the optical axis between images, or if filters are moved or replaced, a new flat frame (or master flat frame) should be created to calibrate each corresponding light frame. When color filter sets are used, a separate flat (or master flat) should be created using each filter to calibrate its respective images.

Image calibration is a tedious process that requires careful understanding, patience, and lots of practice. The user can be the judge as to whether or not any of the above calibrations are necessary for his or her application. If the signal-to-noise ratio is high enough, a raw image might be acceptable. Often, bias and dark correction are the only steps necessary. If vignetting or dust donuts (the out-of-focus result of a dust spec in the optical path) are noticeable in the image, a flat field calibration might be desirable. In applications such as astronomical photometry, where CCD images are used to count photons, it is mandatory that all electronic, thermal and light-path artifacts be removed as cleanly as possible. In many applications, however, photon counting is not important.

Focusing the Camera
Whether the camera is attached to a telescope or a camera lens, focusing and centering can be the most frustrating and time-consuming part of the imaging experience. There is no way to look through the camera and optical system, so focusing is done by taking an image, inspecting it for sharpness, adjusting the focus, taking another image and repeating this process until the sharpest image is produced. Focusing routines in the software are of great help here. These are similar in usage from program to program, but you may require help from the software manual in order to access them (see "focus mode" or "focus" in your software manual or online help). The camera is not automatically focused in any case.

The software focus routine is designed to take a sequence of exposures unattended while the user makes adjustments to the focusing mechanism of the lens or other optical instrument. To save time in this step, a subframed image is recommended. Use the region of interest (ROI) tool to mark off a small section of the image (in some cases, this is as simple as using the mouse to drag a box around the region) that contains a point of light or edge of some kind. When this ROI is sent to the camera, only that part of the image will be updated during focus exposures. Reading off a small portion of the chip increases the frame rate, allowing the user to focus the camera more quickly. Some focus routines are simple, requiring the user to judge best focus by the apparent image sharpness. Other routines are more sophisticated and display a graphical image of the peak pixel values to aid in determining the best focus.

Shutting Down
At the end of an imaging session, it is important to warm the CCD slowly. Use the temperature control settings in the software to return the CCD to ambient temperature. This may take between 10 and 15 minutes. While the thermoelectric cooler is operating, the heat sink and fans draw heat away from the CCD. Simply turning the cooler off would allow heat to flow in the direction of the CCD and warm it rapidly. Thus, there is a need to regulate the temperature during warm up as well as when cooling down. The CCD will have a longer life if the user makes a habit of keeping temperature changes slow and regulated.

When the CCD cooler temperature reaches ambient, the computer may be powered off. If the camera is to be detached from the computer after use, always remove the cable from the camera head first, and then remove the cable from the computer. When reattaching the camera, reverse the order and plug the cable into the interface card first. In this way, you will reduce the risk of electrostatic shock damage to the camera, since the grounded computer will dissipate any charge from the cable before it comes in contact with the camera head.

Care and Handling of the Camera
Handle your Apogee camera with care, as you would any delicate instrument. The aluminum camera body can be cleaned with a soft cloth and glass cleaner. Never spray liquids directly on the camera; apply cleaning solution to the cloth, then wipe the camera body with the dampened cloth.

Over time the camera's optical window will collect dust and other particles. Clean the window by applying lens cleaner and gently wiping it away with a soft, lint-free cloth or lens tissue; avoid heavy rubbing, which may scratch the coating.

Dust will also collect on the cooling fans located on the back of the camera head. From time to time, it may be necessary to clear away the dust with a small brush. The fans disperse heat as it radiates away from the heat sink. Should the airflow become blocked, the thermoelectric cooler may run a few degrees warmer than normal and the camera body could overheat, causing damage to some of the more sensitive components.

Follow these guidelines for safe operation of the camera:

1. Never connect or disconnect an ISA-bus camera while the computer is running.

2. Always ground yourself to dissipate electrostatic charge before handling the camera and its controller card.

3. As much as possible, avoid contact with any of the electrical components of the camera system, especially connector pins and the controller board edge connectors (or, "fingers").

4. Always tighten down the cable connector screws, both at the computer and at the camera head.

5. If the camera is to be connected to a moving device, such as a mounting stage or telescope, be sure to secure the cable with cable ties and allow enough slack so that the cable connector is not stressed during movement.

6. Always allow the sensor to cool down and warm up slowly.

7. AP7 and AP8 camera owners: Do not expose the SITe CCD chip to direct sunlight for prolonged periods (i.e., removing the lid assembly or leaving the shutter open while out of doors). UV charging can result, causing a gradient in light frames. This effect may last for several weeks.

8. Lightning can damage the camera components, even if it is not a direct strike. Always disconnect the camera and remove it from grounded equipment (such as a telescope) whenever there is thunderstorm activity in the area.