newb - tell me about ISO

I have a Canon SD550 which lets me adjust the ISO when using the manual
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.

Under what conditions would i set this higher or lower? Are there any
general rules about ISO settings? I think my camera goes from 50 to
400. Thanks!

wrote in message
oups.com...
I have a Canon SD550 which lets me adjust the ISO when using the manual
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.
Lower ISO more detail.
Higher ISO more noise less detail.

Under what conditions would i set this higher or lower? Are there any
general rules about ISO settings? I think my camera goes from 50 to
400. Thanks!
If you need to stop something going fast in low light use a high ISO, try it
it the camera you will see the shutter speed rise with the ISO, do the
reverse to blur a moving object.

Try it at various settings and make your own choice as to which sort of
images suit which speed.

It is not necessary to do what everyone else tells you to.

Jem

-------------------------------------
Birmingham Independent Photographers
http://bip.wikispaces.com/

wrote in message
oups.com...
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.


Less detail actually; the noise obscures the fine detail.

wrote:
I have a Canon SD550 which lets me adjust the ISO when using the manual
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.

Under what conditions would i set this higher or lower? Are there any
general rules about ISO settings? I think my camera goes from 50 to
400. Thanks!

You can look at ISO as a measure of sensitivity.
Named ISO because it refers to a standard. (ISO stand for International
Standards Organization).

With digital, and simplifying, a higher ISO is accomplished amplifying
the signal of the sensor, so you can with less light or less time
achieve the same signal.
Of course, when you amplify a sensor signal, you also amplify the
noise.
This is only a simplifying way to put things.


al-Farrob
http://www.al-farrob.com
new photos every week

On 29 Mar 2006 11:30:14 -0800, "
wrote:

I have a Canon SD550 which lets me adjust the ISO when using the manual
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.

Under what conditions would i set this higher or lower? Are there any
general rules about ISO settings? I think my camera goes from 50 to
400. Thanks!

Al-Farrob has it pretty right.
Higher (or lower) ISO doesn't equal more detail.
Higher ISO does mean more noise, which can hide detail.
The ISO rating is a measure of the sensitivity of the sensor (digital
or film). A higher ISO means the sensor needs less light to make a
properly exposed image; it also means more amplification is used,
which increases noise.
You might use a higher ISO if a lower one would mean too long an
exposure. Upping the ISO will let you use a faster shutter speed for
the same exposure; it will also let you use a smaller aperture to gain
depth of field. But this also means more noise.

You've already bought the camera, so taking pictures is virtually
free. Take lots, and experiment. Your idea of what's "good" will
differ from others'. So take lots of pics, and learn from the results.
--
Bill Funk
replace "g" with "a"

wrote:

I have a Canon SD550 which lets me adjust the ISO when using the manual
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.

Under what conditions would i set this higher or lower? Are there any
general rules about ISO settings? I think my camera goes from 50 to
400. Thanks!

Don't know where you got the idea that higher ISO "leads to more detail".
ISO is the digital equivalent of film speed with film, if that means
anything to you. It is a measure of sensitivity--the higher the ISO the
greater the sensitivity but you pay for that increase with increased noise
in digital cameras or grain in film cameras.

There's a relationship between aperture, shutter speed, and ISO. If you
hold the ISO constant and change the aperture one stop the shutter speed
has to be slowed by a factor of two, so for example if you're able to shoot
at f/4 and 1/250 with ISO 200, then changing the shutter speed to 1/500
would require that you either change the aperture to f/2.8 (the aperture
numbers are not linear--there's an explanation at
http://www.uscoles.com/fstop.htm) or change the ISO to 400. Similarly if
you change the ISO to 400 then you'd have to either change the shutter
speed to 1/500 or the aperture to f/5.6. Or if you change the aperture to
f/2.8 then you'd have to either change the shutter speed to 1/500 or the
ISO to 100.

As a general rule you want to use the lowest ISO that will give you the
shot. Not something to agonize over though--go out and shoot at different
ISO values and examine the result and pretty soon you'll get used to using
it.

--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)

Bill Funk wrote:

The ISO rating is a measure of the sensitivity of the sensor (digital
or film). A higher ISO means the sensor needs less light to make a
properly exposed image; it also means more amplification is used,
which increases noise.

I think what is really happening is that the sensor sensitivity can't
really change, all you are doing is exposing further down into the
blacks. Then you can amplify that signal to get the values back up to
respectability, but a lot of amplification gives more noise. If I'm
wrong about this, I will eat my sensor, but it's a good description of
the result.

Gary Eickmeier

Jem Raid wrote:
wrote in message
oups.com...

I have a Canon SD550 which lets me adjust the ISO when using the manual
settings. I understand that a higher ISO leads to more detail in the
photo but can also lead to more 'noise' in the image.

Lower ISO more detail.
Higher ISO more noise less detail.
Noise does not necessarily obscure detail, unless the
signal-to-noise ratio is quite low. The main factor in
detail (i.e. resolution) is the number of pixels.


Under what conditions would i set this higher or lower? Are there any
general rules about ISO settings? I think my camera goes from 50 to
400. Thanks!

If you need to stop something going fast in low light use a high ISO, try it
it the camera you will see the shutter speed rise with the ISO, do the
reverse to blur a moving object.

Try it at various settings and make your own choice as to which sort of
images suit which speed.

It is not necessary to do what everyone else tells you to.

Jem

-------------------------------------
Birmingham Independent Photographers
http://bip.wikispaces.com/