David Arnstein wrote:
The digital cameras that I have seen have a feature that allows the
user to choose an ISO setting. I would like to know what this feature
does, since I suspect that it is useless.

My concern is that setting a high ISO number simply
1. Causes the camera to take pictures that are quite dark
2. Post processes the picture by increasing the brightness, in
software.

If this is the case, then I prefer to increase the brightness myself,
in Photoshop.

On the other hand, if the ISO adjustment on the camera actually
changes the physical properties of the photosensor, then it's a
different story.

I'd like some feedback on this before I spend my time experimenting
with different ISO settings.

Vastly oversimplified:
The ISO number is like an amplifier volume setting. The larger the
number the 'louder' the light output from the sensor. And, like a sound
amplifier, excessive settings often produce very distorted, and
'clipped' output. The lower the ISO setting, the more light you need
for a usable picture, but the higher the setting, the more the output
from the sensor is amplified, and the more 'noise', and 'distortion' you
will see. Many cameras use software to improve the image quality, and,
since they have access to the original output from the sensor, they can
usually do this better than Photoshop.


--
Ron Hunter