optical and image acquisition systems
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PROTEL PROJECT
Optical and image acquisition systems
Paraschiv, P., Popescu, P., Nedelcu, A., Badescu, O.
Astronomical Institute of Romanian Academy
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Introduction The autonomous module for polar astronomical surveys PROTEL, represents an
automatic telescope, designed to work without human intervention in conditions of low temperature, imposed by the polar environment. Astro-climate studies have indicated an annual average temperature falling down to -25C, in the area where the instrument is intended to be sited. As a result we have used special kinds of materials, optical components, electronic devices and operating systems adapted to work in extreme cold. The complete lack of human participation imposes a fully automatic, easy to use instrument.
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Optical tube
The optical tube is a OGS - Ritchey Chretien 14.25" f/8 telescope, adapted to work at low temperatures (40C)
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Optical tube
Why RC?
• Where versatility is the key, it seems that Ritchey-Chretien is the best choice, as it combines compact size, light weight and excellent image quality in one design.
• The Ritchey-Chretien is coma-free, whereas the Schmidt-Cassegrain, Newtonian and Classical Cassegrain are not. The RC design utilizes hyperbolic primary and secondary mirrors which correct coma.
• The OGS Ritchey-Chretien system has a flatter field than
production SC systems because of its lower secondary amplification factor, 2.9x versus 5x. The resultant lower f-number also provides the RC with a wider field.
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Optical tube
Why RC?The following graphic shows spot diagrams of 1/2 degree off-axis star images
produced by a 10" f/8.5 Ritchey-Chretien, a 10" f/10 Schmidt-Cassegrain, an f/5 Newtonian and an f/8 Classical Cassegrain.
The superior image quality of the Ritchey-Chretien design is obvious
f/8.5 Ritchey-Chretien
f/10 Schmidt-Cassegrain f/8 Classical Cassegrain f/5 newtonian
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Optical tube
Why RC?• It is the optical design chosen for nearly all new, state-of-
the-art observatory telescopes, and is the same optical system as that used in the Hubble Space Telescope.
• Because the Ritchey-Chretien design has only two air-to-glass surfaces (compared to 4 for the SC) and no refracting elements, it has less light loss and a greater spectral range than the Schmidt-Cassegrain making the
RC ideal for use with CCD cameras.
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Image acquisition system
CCD camera ProLine PL-4240-1-B
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Image acquisition system
Camera System Performance• ProLine PL4240• PC Interface USB 2.0• Selectable download speeds up to 12 mega-pixels/sec • Downloading time: 1 second(focusing) / 20 seconds(acquiring
images)• Digital resolution :16 bits at all speeds• Read Noise: 8 – 11 electrons RMS typical (low download speed)• Cooling: Thermoelectric cooler with forced air: 55-60° C below
ambient temperature• Dark Current <1 e-/pixel/sec (-30° C)• Operating Environment Temperature: -25° to 35°C. Relative
humidity 10 to 90% noncondensing• Shutter 65mm Uniblitz shutter / MTBF = 1 million cycles
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Image acquisition system CCD Specifications
• CCD: E2V CCD42-40-1-368 back illuminated
• Array Size: 2048 x 2048
• Pixel size: 13.5 micron
• Linear Full Well: 100,000 e-
• Dynamic Range: 82 dB
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Image acquisition system
Spectral range
This is ours
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Image acquisition system
Noise
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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Optical and image acquisition systems Conclusions
• The optical field of such a telescope endowed with a corresponding CCD camera is of 28.6 x 28.6 arcminutes, having an angular pixel resolution of 0.3 arcseconds/pixel.
• Astronomical data are collected in the internal memory of an images acquisition module, coupled by a CCD camera ProLine PL-4240-1-B Back-illuminated, CCD Sensor e2v 4240, Grade 1
• Using PROLINE PL-4240-1-B CCD Sensor with short downloading time (2 seconds / 20 seconds) it is possible to obtain more observational efficiency.
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008
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• Thank you!
PROTEL PROJECT
The 3-rd International Symposium on Polar Scientific Research, Bucharest, 27 June 2008