Luminous Landscape Forum
The Art of Photography => The Coffee Corner => Topic started by: Isaac on January 30, 2015, 01:46:33 pm
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…will be Pointed at the Skies in 2022 (https://www6.slac.stanford.edu/news/2015-01-09-world%E2%80%99s-most-powerful-camera-receives-funding-approval.aspx)
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Who's polishing the mirror this time round?
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Have they made a neck strap for it? I don't think a wrist strap will be strong enough. ;)
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Who's polishing the mirror this time round?
The irony of this is that Hubble is a far superior instrument due to its necessary upgrades than it would've been if that notorious mirror had been polished correctly. It wasn't designed to be upgraded…we did the initial one because we had to, and then all the others because we knew we could.
-Dave-
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The irony of this is that Hubble is a far superior instrument due to its necessary upgrades than it would've been if that notorious mirror had been polished correctly. It wasn't designed to be upgraded…we did the initial one because we had to, and then all the others because we knew we could.
-Dave-
Hubble is indeed an incredible achievement and in hindsight it is probably quite fortuitous that there was the problem with the mirror, but I still wonder how it managed to happen given everything else worked so well.
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Hubble is indeed an incredible achievement and in hindsight it is probably quite fortuitous that there was the problem with the mirror, but I still wonder how it managed to happen given everything else worked so well.
It was a goof-up by the contractor hired to do the polishing job. Fortunately they did a good job of doing it wrong. :) Which made it easier to design corrective optics. Nowadays Hubble's instruments are tuned to the actual mirror geometry and the corrective optics are gone.
-Dave-
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If nothing else, the signal corrections to the images from the original mirror showed the potential for deconvolution sharpening.
Dave
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For those curious about this camera's sensor and other technologies, see http://www.lsst.org/lsst/science/concept_camera
As usual with astronomical cameras, it uses CCD's: lots of 40x40mm ones butted together, with 10 micron pixel pitch. The butting gaps are only promised to be "sub-millimeter", so there will be very visible join lines that would be unacceptable for "artistic" photography.
But what about the worse noise floor of CCD's compared to modern CMOS sensors?
The focal plane array operates at a temperature of approximately -100°C to achieve desired detector performance. The focal plane array is contained within an evacuated cryostat, which incorporates detector front-end electronics and thermal control.
So it sounds like both sensor dark current noise and thermal noise in the analog electronic signal path are controlled in a way that us "hand-holdable camera" photographers can only dream of.
Also, fulfilling the dreams of many forum commentators, the sensor is circular! Or rather, the 189 individual square sensors are arranged to cover the image circle of the telescope, with minimal overhang.
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Who's polishing the mirror this time round?
Since you asked: the mirror was designed and is being manufactured at the University of Arizona in its Stewart Observatory Mirror Lab, under the football stadium: http://mirrorlab.as.arizona.edu/about/news/LSSTAug
(But since this mirror does not have to be light enough to put into orbit, the special challenges of the Hubble Telescope mirror should not apply.)
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Well, bathing your sensor support in liquid nitrogen ought to take care of the thermal read noise! I can't imagine an easy way of uniform cooling to minus 100 C other than by liquid. Peltiers are great, but in the usual iterations, don't go to temperatures that low -but what do I know, I am a biologist!
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Well, bathing your sensor support in liquid nitrogen ought to take care of the thermal read noise! I can't imagine an easy way of uniform cooling to minus 100 C other than by liquid. Peltiers are great, but in the usual iterations, don't go to temperatures that low -but what do I know, I am a biologist!
Liquids in the optical path might be a problem, but one solution is using liquid nitrogen indirectly to cool an exchange gas, either nitrogen of helium, which gas then flows over the components to be cooled. For example:
http://www.oxford-instruments.com/products/cryogenic-environments/optical-cryostats-for-spectroscopy/nitrogen-cryostats-77k/nitrogen-cryostat-77k-sample-in-exchange-gas-optis
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Or you can mount the sensor to an aluminum or copper baseplate that has channels for the liquid nitrogen to flow through.
Just like the liquid CPU coolers, except using liquid nitrogen instead of ethylene glycol solution.