Re: News - Picture of Shuttle and ISS Silhouetted against Sun
- From: prep@xxxxxxxxxxxxxxxx
- Date: Tue, 03 Oct 2006 01:10:52 +0800
OM <om@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> writes:
On Mon, 2 Oct 2006 04:22:12 GMT, henry@xxxxxxxxxxxxx (Henry Spencer)
wrote:
Yes, even for light-gathering power, despite the smaller aperture,
because the CCD needs a lot fewer photons to form an image than the
films the pros were using back then.
...On the other hand, there's two things about CCD that still makes
some astronomers prefer film:
Who? Brad?
1) The longer you expose a CCD in extreme low light, you get more
noise than you would with film. In addition, colors towards the red
end of the spectrum tend to get overly exaggerated as the exposure
progresses.
Yes, but it is an non issue. You take multiple exposures and stack
them. Set each exposure time so dark noise ~= readdown noise, soot N
frames and improve your SNR by rootN. The red is not a problem,
getting blue and UV IS. A Lumogen coating fixes that.
2) Cold-packing a CCD does absolutely nothing to improve the light
sensitivity, but freezing that film and then keeping the camera body
cold with an ice bag does improve the emulsion sensitivity by a
significant amount.
You dont gain any Q, but you drop noise a LOT. A HUGE LOT. A friend
of #1 daughter designed a CCD camera that had just under 1e RMS noise.
OK, operating in the antactic helped ;)
Hypering film helps by getting rid of charge traps and other losses
in the AgX system, but have never got near the Q of a good CCD.
--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.
.
- References:
- Prev by Date: Re: Moon landing photos
- Next by Date: Re: We're coming up on the 10th anniversary of ssh, kids!
- Previous by thread: Re: News - Picture of Shuttle and ISS Silhouetted against Sun
- Next by thread: One Small Step The Missing "A"
- Index(es):
Relevant Pages
|
