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CCD & CMOS cameras

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How Deep Can You Go?
 High-quality CCD camera promises converting of majority of incoming light into information. Another important feature is keeping system-induced noise as low as possible to maintain good signal to noise ratio. Regulated chip cooling and system read noise limited only by the CCD chip itself is a must for scientific-grade instruments. So what is the limiting magnitude for typical backyard telescope?

The following images demonstrate the reach offered by sensitive, cooled astronomical CCD camera to astronomers. The instruments used were the 35 cm (approx. 13.8 inch) Newtonian telescope with 166 cm focal length (f/4.7) and G2CCD-0400 camera with Kodak KAF-0402ME CCD chip. Observing conditions were average.

M1 field

The first field shows the neighbor of the M1 Crab Nebula, captured without filter. DSS-2 image of the same field in the red light is provided for reference. Although stars on the DSS-2 (Digitized Sky Survey - 2) image has better FWHM (Full-Width Half-Maximum) due to significantly greater telescope aperture and also better seeing, the limiting magnitude is almost the same.

The nebulosity on the DSS-2 image looks “sharper” because of the red filter used—the nebula filaments shines in the red Ha line.

Unfiltered M1 “Crab Nebula” field captured by G2CCD-0400 (left) and DSS-2 red-light image (right)

Brightness of both marked stars is 21m. The contrast of the image areas with the marked stars was enhanced to make both stars easier visible.

The G2CCD-0400 image was captured on the January 24th, 2006. Exposure time was 50 min, from 21:10 to 22:00 UT. The exposure was co-added from 100 exposures (30 s each) to eliminate telescope mount errors. Resulting S/N ratio is still very good thanks to very low camera read noise.

NGC 2419 field

The filed of globular cluster NGC 2419 shows slightly lower reach—approx. 20.7m—compared to 21m of the DSS-2 red-light image. The star FWHM of the DSS-2 image is noticeably better due to better seeing on the Mt. Palomar.

Unfiltered NGC 2419 field captured by G2CCD-0400 camera (left) and DSS-2 red-light image (right)

The marked galaxy brightness is 19m. The G2CCD-0400 image was captured on the January 25th, 2006 with exposure time 18 min,

C/2003 WT42 (LINEAR)

The C/2003 WT42 comet magnitude was approx. 14m when the image was taken on February 17th, 2006. The exposure time is 20 minutes, from 20:02 to 20:22 UT.

Unfiltered 20 min exposure of C/2003 WT42 (left) and corresponding DSS-2 red-light image (right)

Images from G2CCD-0400 captured and processed by Kamil Hornoch.

The Digitized Sky Survey was produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. Acknowledgments.

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