'Lucky' camera creates ground-based images better than Hubble's.(ASTRONOMICAL IMAGING)

Astronomers have taken pictures of objects that are higher in resolution than anything produced by the Hubble Space Telescope (HST), at a fraction of the cost. Researchers at the University of Cambridge (Cambridge, England) and the California Institute of Technology (Caltech; Pasadena, CA), used an adaptive-imaging technique and a camera called "LuckyCam" to obtain the sharpest pictures of stars and nebulae ever produced from a ground-based observatory (see figure).

Images from ground-based telescopes are limited in resolution by the shimmering of the Earth's atmosphere, the same effect that makes stars twinkle. Adaptive-optics (AO) systems enable astronomers to subtract much of the smearing of the image, but so far are most useful only in the infrared part of the spectrum. The LuckyCam is an ultra-low-noise, electron-multiplying, charge-coupled-device (CCD) camera developed by Cambridge imaging researcher Craig Mackay to enable high-resolution imaging at visible wavelengths. The camera is called "Lucky" because it relies on chance imaging of an object when it is least affected by poor atmospheric seeing (see www. laserfocusworld.com/articles/274711 for another instance of this kind of system).

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To capture the images, the astronomers mounted the camera behind an AO system at the 200 in. (5.1 m) Palomar telescope (Mt. Palomar, CA) to record images at rates of 20 to 100 frames per second. The highest frame rate of 100 Hz limited the image to a tiny 512 x 100-pixel field, while the very slow rate of 20 Hz resulted in a field measuring 512 x 512 pixels, or 20 x 20 arcsec of the sky.

A computer program sorted the vast number of images, discarding the majority of them and saving those that were sharpest following AO corrections. The best images were then combined to produce pictures twice as sharp as those taken from Hubble, a feat never before accomplished.

Twice as sharp as Hubble

Much like at other ground-based telescopes, the images produced at Palomar are roughly 10 times less ...