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Megacam is a 36 CCD mosaic camera that will cover a 24' X 24' field of view at the f/5 wide-field focus of the converted 6.5 m Multiple Mirror Telescope. The mosaic is a 9 X 4 array of thinned 2048 X 4068 pixel CCDs with 13.5 micrometer pixels. The CCDs are dual-output EEV devices in a custom package to allow the devices to be closely butted on all four sides. The dewar will be mounted to a 2 m diameter assembly that contains the filter wheels (for 30 X 30 cm filters) and the shutter. Telescope guiding will be accomplished with two additional CCDs mounted at the edges of the focal plane. The guider CCDs will be operated slightly defocused, one on either side of focus, to allow simultaneous focusing and guiding. Guide stars will be selected by reading out the full guider frame, after which only a small area surrounding the guide star will be read out. Our simulations show that the defocused guide star images will also be useful for low order wavefront sensing, allowing corrections to the telescope collimation. We are developing a new CCD controller capable of reading the full Megacam in 24 seconds. This controller will also be used to operate the guide chips.

The Hectochelle will be a fiber-fed, multi-object spectrograph for the post-conversion MMT which will take 255 simultaneous spectra at a resolution of 32,000 - 40,000. The absolute efficiency, including optical fiber losses, is predicted to be 6% - 10%, depending on the position of a line within a diffractive order. In one hour, features with 60 mangstrom should be resolved in mR equals 18 stars with a signal to noise of 10.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The S.A.O. Megacam focal plane will consist of 36 large CCDs (2K X 4.5K format), each with 2 output portsrunning at pixel rates up to 200 kHz. The unbinned data field is thus as large as 324 megawords and is presented at a sustained data rate during readout approaching 28 megabytes/sec. We have developed a simple camera controller to deal with the problem of handling so many channels and their digitized outputs at fairly high speeds.We also present some results from ongoing efforts to optimize the 200 kHz signal processing chain for low noiseand low crosstalk.Keywords: camera, electronics, controller, CCDThe S.A.O. Megacam"2 represents an order-of-magnitude jump in the scale of the electronic controllers andsignal processors that we have used in the recent past. In addition to that large number of video channels (72)to be accommodated, we desired to increase the readout rate to approximately 200 kHz in order to get the readoutlatency times down to comfortable levels, and to adapt the same controller hardware to allow autoguiding fromtwo additional CCDs in the main focal plane. It soon became evident that adapting a commercial CCD controllerto this vastly expanded task would be very problematic if not impossible. Thus, we were faced with the task ofdesigning and building most of the camera in-house. Fortunately, based on our experience in past years withcustom controller development, we were able to undertake this job with some prospect for success by basing thedesign on simple ROM/RAM modules for pattern generation, with which we had considerable favorable experience.We were quite confident that such a digital design, using proven techniques and incorporating the latest in digitalcomponents (such as gate arrays) would ultimately give us a very reliable, compact digital core for our controller.More challenging would be providing a high-speed fiber-optic link to the computer for the huge data stream anddeveloping the higher speed analog signal processing chain we desired.