Date: Wed, 19 Feb 2003 16:57:41 +0000Hi Janus,
From: Janus van Helfteren
Subject: [PRODIG]
Hello list , here is an idle question .
When one adjusts 'iso' setting on , say, an S2 , what actually happens.
ie . with film bigger grain accepts light more quickly (I think) , hence fast film being grainy and slow film having finer grain.
So how does that work on a ccd ? in simple english ? Cos we have noticed 'grainier' shots at higher iso settings , which doesnt make sense to me.
yours , confused
Janus
increasing the ISO speed of a CCD or CMOS sensor means turnig up the amplification at some point in electrical processing, to compensate for smaller signals from the sensor. This also means that noise (i.e., random fluctuations of the signal with time, inevitable due to laws of physics, but very dependent on technology) is amplified along with the useful signal. Regardless of the ISO-setting, the size of the "grain" remains the same: one pixel. There is an additional aspect: Each individual sensor for each pixel has slightly different properties - no way to make them really alike. This probably also causes some "grain", but since the pattern is the same for each exposure, it might be compensated automatically by subtracting the result of a dark exposure with the same exposure time - as far as I know, cameras do that, at least for long exposure times.
Otto
--
//_ Dr. Otto PETER Institute for Applied Physics
.0^0__ University of Innsbruck
/_ \ / Technikerstr. 25
\____/^ A-6020 Innsbruck, Austria
_/|_ Tel.: +43-512-507-6408, Fax: +43-512-507-2922
===============================================================
GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
