Wolfgang Beisker
München, Germany

Since years the recording of occultations was dominated either by visual inspection or by commercial videocameras. For precise occultation recording, as it is necessary for determing stellar diameters or planetary atmospheres, the Iota Occultation Camera (IOC) has been developed to record 12 Bit images fast enough. However, the relatively high price of this system in combination with the complex handling of a true scientific camera device has limited its use.
In this report I will present data on the use of consumer webcams such as the Philips Toucam 740K®, the 3Com HomeConnect® and the Logitech Quickcam 4000® system for occultation work. All these cameras have a colour CCD element with about 640x480 pixels as well as an USB 1.1 connection to the computer. This makes them an ideal system for field work, if connected to a notebook computer. The data are already digital data, the cameras are extremely small and cheap. The human interface is relatively simple to handle, because they are built for the large consumer market. They allow imaging without modification with a longest intergration time of 0.2 or .25 seconds. Imaging as fast as with 10 or 15 frames per second is possible. Many of theses cameras use the high sensitivity CCD HAD® chip in ¼ inch size from Sony, which is well suited even on telescopes with short focal lengths. Imaging is possible in three colors, which are well separated in case of the Sony chip. However, color imaging reduces the sensitivity of the system by a factor of more than three. For the Sony ICX098BQ chip an electrically identical chip is available, the ICX098BL. The Toucam has been modified, resulting in an fastly increased sensitivity comparable to the IOC. Cooling is not really required with these chips due to short integration times.
Only the 8-Bit digitization hampers a little the use of the systems, but coadding of images can result in about 10 Bit data, which is in most cases enough even for atmosphere work on planets.
The big advantage of the Webcams is the direct digitization, which is more accurate than standard video processing. In recent times, an integrating videocamera from Mintron has been used for astronomical imaging. However, the analog video signal has been digitized, which is not as reproducable as the webcam's direct technology.
 
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