1.5 gigapixel camera

http://www.newscientist.com/article.ns?id=dn7511

RichA wrote:
http://www.newscientist.com/article.ns?id=dn7511

OK, so how does bigger make it more sensitive
in that it "dwarfs the sensitivity of the Hubble
Space Telescope"?

As a magazine, New Scientist seems to be following in the footsteps of
Scientific American as it descends into banal obscurity. IMO they should
just change the name to Global Warmed-Over and be done with it.

Richard F.L.R.Snashall wrote:
RichA wrote:

http://www.newscientist.com/article.ns?id=dn7511


OK, so how does bigger make it more sensitive
in that it "dwarfs the sensitivity of the Hubble
Space Telescope"?

On Thu, 16 Jun 2005 18:10:38 -0400, "Richard F.L.R.Snashall"
wrote:

RichA wrote:
http://www.newscientist.com/article.ns?id=dn7511

OK, so how does bigger make it more sensitive
in that it "dwarfs the sensitivity of the Hubble
Space Telescope"?

I have no idea. What is the size of the telescope being mated
to the camera? I also read the other day of a balloon lofting of
a 6.5 meter mirror telescope. This sounded at bit too big to be real.

WOW! Geeeeeeee! HOLY MOSES. Golly. hMMMMMMM.
uh? weell. oh. uh ah. frppppppppp. uhhhhhhhh. ohhhhhhhhh?
seeeeeee? well. Geeeeeeeezuz!


RichA wrote:

http://www.newscientist.com/article.ns?id=dn7511

On Fri, 17 Jun 2005 02:07:12 -0400, RichA wrote:

I have no idea. What is the size of the telescope being mated
to the camera? I also read the other day of a balloon lofting of
a 6.5 meter mirror telescope. This sounded at bit too big to be real.

The Gaia telescope is very unusual. It is actually two telescopes with a
common focal plane. Each objective consists of a rectangular mirror. The
entrance aperture is 1.4 x 0.5 meters. The telescopes have very long
focal lengths- 46.67 meters. With the 10um pixels on the sensor, this
means the diffraction pattern is oversampled about six times. This is
because the instruments are optimized for astrometry, and placing a
stellar image on many pixels increases the accuracy of the calculation.

The spacecraft will be spinning, so the image drifts across the focal
plane. A technique called time delay integration is used, where the data
in the CCD array are shifted at the same rate. In this way, a very long
image is being continuously shifted out. This method is used by some
amateurs, too, allowing an image to be generated with a stationary scope
(since the sky is slowly shifting across the image plane). BTW, apropos
your recent comments on CMOS versus CCD, this TDI technique can only be
done with a CCD, since you can't shift one pixel to another using CMOS.

The instrumental target is stars magnitude 20 and brighter, so the HST
is considerably more sensitive in actual application. In terms of simple
instrumental sensitivity, both systems use sensors with similar QE. HST
is usually used for long, deep exposures. Gaia will have an integration
time of just a few seconds, optimized for collecting huge amounts of
astrometric and photometric data in a relatively short time.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

RichA wrote:
On Thu, 16 Jun 2005 18:10:38 -0400, "Richard F.L.R.Snashall"
wrote:


RichA wrote:

http://www.newscientist.com/article.ns?id=dn7511

OK, so how does bigger make it more sensitive
in that it "dwarfs the sensitivity of the Hubble
Space Telescope"?


I have no idea. What is the size of the telescope being mated
to the camera? I also read the other day of a balloon lofting of
a 6.5 meter mirror telescope. This sounded at bit too big to be real.

Does sound weird. I bet UC/Cal Tech are going to rip that spare 10m Keck
mirror off it's mountings and hang it from a balloon next; can't be left
behind in the Science Race.