optical and image acquisition systems

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

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.


Optical tube

The optical tube is a OGS - Ritchey Chretien 14.25" f/8 telescope, adapted to work at low temperatures (40C)


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.


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


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.


Image acquisition system

CCD camera ProLine PL-4240-1-B



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


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



Spectral range

This is ours



Noise


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.


• Thank you!

PROTEL PROJECT


optical and image acquisition systems

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