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MMT All-Sky Camera: Wide-Angle, Low-Cost, and Simple

The MMT All-Sky Camera is a low-cost, wide-angle camera system that is frequently updated and requires no mechanical parts. With the StellaCam II camera and Fujinon lens, it offers high-quality images. The system includes hardware components such as fiber-isolated video and RS232, a framegrabber, a computer, and software for image processing and archiving. The system is cheap, robust, sensitive, and provides rapid response.

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MMT All-Sky Camera: Wide-Angle, Low-Cost, and Simple

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  1. The MMT All-Sky CameraT. E. Pickering • Low cost ⇒ ~$3500 • Wide angle ⇒ ~150˚ • Simple ⇒ No mechanical parts • Frequently updated ⇒ Every 10 sec

  2. Camera: StellaCam II ⇒ Low-noise, variable gain video camera ⇒ On-board integration up to 256 frames ⇒ Auto-iris support and RS232 control Lens: Fujinon 1.4--3.1mm f/1.4 ⇒ Inexpensive (~$200) C/CS mount ⇒ Automatic iris Enclosure: Pelco EH2515 ⇒ Standard CCTV enclosure, widely available ⇒ Inexpensive (~$130) ⇒ Well-sealed against dust and moisture Camera Hardware

  3. Computer Hardware Fiber-isolated Video and RS232: ⇒ Need optical isolation to protect against lightning ⇒ TeleByte duplex RS232 fiber modems ⇒ Luxcom OM-7 video fiber modems ⇒ Better video quality than long run of coax Framegrabber: FlashBus MV PCI ⇒ Color with lower noise monochrome mode ⇒ Linux driver and SDK available Computer: Shuttle SFF PC ⇒ 2.8 GHz Celeron w/1 GB RAM ⇒ Nothing special, just need PCI slot and enough RAM for movies

  4. Software • FlashBus SDK from Integral Technologies used to build tools for grabbing and averaging frames into FITS images. • Open source ImageMagick tools used to convert FITS images to GIF and PNG, apply markup to images, and to create animated GIFs. An animated GIF of the 100 most recent frames is created whenever a new image is acquired. • No automatic gain or exposure control on camera so master control script must monitor image brightness and adjust camera parameters accordingly. During the day the automatic iris control is sufficient and works well. • Images are archived into DivX format AVI files at sunrise and sunset each day. This format allows us to compress 4000+ images (~1.2+ GB) into single 12-20 MB files while retaining good image fidelity.

  5. How does it do? Pretty good during the day....

  6. Pretty darn good at night....

  7. Can easily see clouds in the dark....

  8. Handles the bright moon reasonably well....

  9. Catches meteors, satellites, and zodiacal light....

  10. Sometimes there are surprises....

  11. Calibrating Image Coordinates • In the images shown, the red cross denotes the pointing position of the MMT. • First step is to find zenith point in image and convert (x,y) to (r,θ) within image. • Then it is easy to map azimuth onto θ (we use just a zeropoint offset) and zenith angle onto r (we fit a cubic polynomial).

  12. Radial Distortion in Lens RMS about the full geometric transformation is 1.2 pixels

  13. In Summary... • Our system is pretty cheap: The capital cost of the equipment was less than $3500 and the software requirements are fairly simple. • Our system is robust: It has operated almost without hitch for the past 8 months. • Our system is sensitive: At night with a maximum 8.53 sec exposure and a moderate gain setting the system can easily reach 5th mag or fainter in the visual. • Rapid response comes in handy: The 10 sec duty cycle provides nearly continuous temporal coverage. This is helped catch light precipitation that might otherwise have gone unnoticed. • See http://skycam.mmto.arizona.edu/ for data and movies.

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