ISO & exposure comp. -- aren't they redundant?

Charles Packer wrote:
Where is the logic in all of this? In the digital world,
aren't ISO and exposure compensation redundant, anyway?


ISO - in effect a choice between speed and noise

exposure comp - the ability to intervene when the automatic
exposure algorithm does not serve well enough.

In what way are these redundant?

BugBear

bugbear schrieb:
Charles Packer wrote:
Where is the logic in all of this? In the digital world,
aren't ISO and exposure compensation redundant, anyway?


ISO - in effect a choice between speed and noise

exposure comp - the ability to intervene when the automatic
exposure algorithm does not serve well enough.

In what way are these redundant?

Back in analog days they would have been. You could just lie to the
camera about the speed of the film to make it under or overexpose. In
digital days this is not the case anymore :-)

kruemi

--
Agfa isolette, EOS 40D
http://flickr.com/photos/kruemi
And a cool timekiller: http://www.starpirates.net/register.php?referer=9708

Marco Tedaldi wrote:
bugbear schrieb:
Charles Packer wrote:
Where is the logic in all of this? In the digital world,
aren't ISO and exposure compensation redundant, anyway?

ISO - in effect a choice between speed and noise

exposure comp - the ability to intervene when the automatic
exposure algorithm does not serve well enough.

In what way are these redundant?

Back in analog days they would have been. You could just lie to the
camera about the speed of the film to make it under or overexpose. In
digital days this is not the case anymore :-)

If you set the shutter speed and aperture,
then alter the ISO on your digital camera,
you will indeed alter the exposure, at least in
JPEG output.

BugBear

bugbear schrieb:
Marco Tedaldi wrote:
bugbear schrieb:
Charles Packer wrote:
Where is the logic in all of this? In the digital world,
aren't ISO and exposure compensation redundant, anyway?

ISO - in effect a choice between speed and noise

exposure comp - the ability to intervene when the automatic
exposure algorithm does not serve well enough.

In what way are these redundant?

Back in analog days they would have been. You could just lie to the
camera about the speed of the film to make it under or overexpose. In
digital days this is not the case anymore :-)

If you set the shutter speed and aperture,
then alter the ISO on your digital camera,
you will indeed alter the exposure, at least in
JPEG output.

Sure. But that is not, what the OP asked about. We have three variables.
Sensitivity (iso)
Aperture
Exposure time

If we change one we have to change (at least) another one too the get
the same result. Thats nothing new.

The thing is, that if I change the ISO-setting on a digital camera, it
change two things in fact. I change the "sensitivity" of the sensor and
tell this to the camera so it's taken into account. So in the end
effect, nothing but noise-level should change.

If I change the setting on an analog camera (without changing the film),
the exposure is changed.

IF I set my camera to "manual" no automatics apply at all, so you have
to care for the exposure for yourself. With manual setting you don't
need EV-correction.

Marco

--
Agfa isolette, EOS 40D
http://flickr.com/photos/kruemi
And a cool timekiller: http://www.starpirates.net/register.php?referer=9708

Marco Tedaldi wrote:
bugbear schrieb:
Marco Tedaldi wrote:
bugbear schrieb:
Charles Packer wrote:
Where is the logic in all of this? In the digital world,
aren't ISO and exposure compensation redundant, anyway?
ISO - in effect a choice between speed and noise

exposure comp - the ability to intervene when the automatic
exposure algorithm does not serve well enough.

In what way are these redundant?

Back in analog days they would have been. You could just lie to the
camera about the speed of the film to make it under or overexpose. In
digital days this is not the case anymore :-)
If you set the shutter speed and aperture,
then alter the ISO on your digital camera,
you will indeed alter the exposure, at least in
JPEG output.

Sure. But that is not, what the OP asked about. We have three variables.
Sensitivity (iso)
Aperture
Exposure time

If we change one we have to change (at least) another one too the get
the same result. Thats nothing new.

The thing is, that if I change the ISO-setting on a digital camera, it
change two things in fact. I change the "sensitivity" of the sensor and
tell this to the camera so it's taken into account. So in the end
effect, nothing but noise-level should change.

That's if you have the camera set to auto expose.
Then it will compensate for you changing the ISO sensitivity by altering
the shutter speed or aperture or both to get the same mid-tone exposure.
The same happens with film cameras with full automatic control of both
aperture and shutter speed.
Most of the early AE film cameras only have "aperture priority" AE which
alters the shutter speed to meter for an ISO/ASA change, simply because
the camera body had no way of altering the aperture.

If I change the setting on an analog camera (without changing the film),
the exposure is changed.

That's only if your film camera isn't set to (or doesn't have an) AE mode.
The same thing will happen with most digital cameras set to manual exposure.

IF I set my camera to "manual" no automatics apply at all, so you have
to care for the exposure for yourself. With manual setting you don't
need EV-correction.

That's because there's nothing the camera can do to change the exposure
settings without being in one of it's AE modes.