Thanks Chuck, all DCs perform best at low ISO (less noise), CCD require
light to charge up, less light means less charge and the output will be
less. The noise is also related to the whole electronics circuit design like
the noise of the amplifier to enlarge the signal and other components'
noise.
Consider a white level to charged a CCD can gives an output of 1000uV (just
an example, I think CCD gives much less), with increasing of ISO to 400 the
CCD can only output 250uV. With a shadow light level that original gives an
output of 4uV now it only gives 1uV. At low output level the noise of the
circuit come into play, say if the noise of the amp is 2uV you can no longer
resolve the shadow. Actually the CCD itself also has dark noise, a light
level of too low may be already very close to this level and hard to
resolve.
Obviously if the noise level is too high, the resolution will also be
affected.
C.H.Ling
----- Original Message -----
From: "Chuck Norcutt" <norcutt@xxxxxxxxxxxxx>
To: "C.H.Ling" <chling@xxxxxxxxxxxx>; "Olympus mail list"
<olympus@xxxxxxxxxxxxxxx>
Sent: Sunday, January 21, 2001 11:16 AM
Subject: [OM] Some E-10 Test shots
> Nice work C.H. I noticed that some say "ISO 80" and some say "ISO 160"
> which leads me to a question I've been meaning to ask for some time.
> What in blazes does it mean to have multiple ISO speed ratings on a
> digital camera?
>
> With film we'd be trading off something like grain or less accurate
> color for the sake of increased speed. What are we trading off with
> digital? resolution? What's actually happening... pixel combining to
> increase sensitivity or some such thing?
>
> Chuck Norcutt
> Woburn, Massachusetts, USA
> (where it's starting to snow, snow, snow)
>
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