Correct use of ISO

[Marcel]

Hi all!
I finally got my Canon 350Dwith the 17-85mm IS USM lens.
I guess I know that with poor light condition and the impossibility of using
flash, such as in a museum, I can up the ISO to 800 and even 1600 with some
noise. However, I don't understand why and when I should up the ISO when
photographing outside by a clear day. I saw in different posts people
shooting at 400 ISO.... Could someone please enlighten me on this matter?
Thanks,
Marcel

[Douglas]

I'm not sure about this model but with a 20D you can set the function in the
camera to auto expand the ISO as needed. The camera will then use the lowest
ISO number given consideration for other variables like shutter speed which
is critical for this camera. Under 1/60th it is almost impossible to get a
clear, sharp photo due to the internal mirror hitting the stops when is
swings up.

Later, as you become more conversant with the functions you might choose to
set your own ISO to force the camera into certain behaviour. The compromise
required for indoor, low light is never going to yeild the same picture
quality as outdoors in good light. In such circumstances where you don't
know the camera's behaviour, letting it make the decissions for you will at
least get usable results.

[=bob=]

Know your camera character first.
Some ppl consider their camera's ISO 400 is ok , some not. .
But to grab a fast shutter speed for freezing moment ppl tend to go to that
ISO speed outdoor [or even ISO 800 :) ]

If you are shooting night scenery ... get the lowest ISO you can ... my S2
Pro ISO 100 is just amazing ... almost 0 noise during 32" exposure.
Again , if the source of lighting you have is the ambient .. crank it up to
the highest acceptable ISO ..
I've seen 350D ISO 800 produced a very ugly grain on skin .. I don't know
its the image compression
or the photographer just started to play with his new toy.

Digital brings a totally new experience in photography. Before your variable
are only 2: Shutter speed and lens aperture only.
Now .. shutter speed, lens aperture and sensor sensitivity
[well . .you can argue you can swap ISO 50 film for scenery, then roll it
and change it to ISO 800 when you shoot sport ]
They just get more interesting by the day :)

Btw .. your IS lens is good for shooting at low speed (1/30" or lower :) )
and you should still get quite a sharp shot.

[Jim]

As with film, you should always use the lowest ISO setting you can
get away with. That's about it in a nutshell :-)

Higher ISO settings introduce noise.. With DSLRs the noise isn't
readily apparent until you get to 800 or 1600, but it's there.

If you have to do serious level adjustments or sharpening on a
high ISO image, the noise grain will quickly become very
visible.

[David]

Hi all!
I finally got my Canon 350Dwith the 17-85mm IS USM lens.
I guess I know that with poor light condition and the impossibility of using
flash, such as in a museum, I can up the ISO to 800 and even 1600 with some
noise. However, I don't understand why and when I should up the ISO when
photographing outside by a clear day. I saw in different posts people
shooting at 400 ISO.... Could someone please enlighten me on this matter?
Thanks,
Marcel
First, a minor nit -- I wouldn't say the concept of "correct" (or the
related concept of "wrong") really applies to this topic. As either
an artist or a photojournalist (and I'm not trying to claim that the
categories don't overlap, either), the final result is what matters.
Anybody who tells you you did it "wrong" while people are raving over
your picture are, well, wrong. Maybe there's a way to have done it
even better, though, and that might be worth learning for next time.

Each camera model is different, but for many uses modern DSLRs produce
near-zero noise up through ISO 400. At least for *small* print uses.
So some people mostly just leave it there.

Also, sometimes the ability to use a higher shutter speed and/or
smaller aperture (larger f-number) is key to a photo, and putting the
ISO up and accept higher noise is worth it. If you're hand-holding a
long lens you might very well want to shoot at 1/500 second at f22 --
which you can't do even in direct sun at ISO 100. If you're taking a
macro shot, you might want to stop down that far, too, plus there's
considerable light loss with the lens extension to focus that close