new to digital - ISO

I' thinking of getting into digital. I'm not sure of something.
I looked at some camera specs and saw
"ISO range (from 100 to 1600 plus ISO 3200 in extended mode)"
Can I assume that the change in speed in fact changes how the image is
stored in some way so that the image when taken will require more or less
light, and when printed/viewed will consequently appear more or less grainy?

Harry Weiss wrote:
I' thinking of getting into digital. I'm not sure of something. I looked at
some camera specs and saw "ISO range (from 100 to 1600 plus ISO 3200 in
extended mode)" Can I assume that the change in speed in fact changes how the
image is stored in some way so that the image when taken will require more or
less light, and when printed/viewed will consequently appear more or less
grainy?

The ISO setting goes to the sensitivity of the sensor. The sensor itself is a
constant gain sensor, but in between it and the analog- digital converters is
a gain section.

1) It sets the amplification of the signal received on the sensors prior to
conversion into digital

2) Its setting is what the metering systems uses along with aperture and shutter
speed to determine if the exposure is correct. In "auto" modes, the camera will
evaluate the light and choose the optimal ISO/shutter speed/aperture. In semi
auto modes such as aperture priority, it will set the shutter speed based on
your choice of ISO and aperture.

Digital sensors have constant "grain" regardless of the ISO. But the noise in
each pixel may be higher as the ISO goes up resulting in 'speckles' due to the
difference in noise in adjacent sensors.

Cheers,
Alan




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