A technical explanation -- Why a camera is "rated" at a particular ISO?

[sbroock]

If a camera or sensor is "rated" at ISO 320 (or 800) is that shorthand for saying that there is no appreciable improvement in signal to noise below that mark?

This isn't meant to revive old threads on what the ranking of the Mysterium (or X) specifically is, but rather more generically -- what does one mean when they assign a specific ISO rating in the first place?

-Scott

 

[Jacek Zakowicz]

Digital ISO

Digital ISO

If a camera or sensor is "rated" at ISO 320 (or 800) is that shorthand for saying that there is no appreciable improvement in signal to noise below that mark?

This isn't meant to revive old threads on what the ranking of the Mysterium (or X) specifically is, but rather more generically -- what does one mean when they assign a specific ISO rating in the first place?

-Scott

It means that , in average setting, average contrast scene, with average balance between highlights and shadows, you'll get nicely balanced exposure i.e. same amount of headroom and legroom(?) off the 18% grey chart level.
Now you should hit wikipedia for the term definition of terms you are not familiar with in the above sentence:thumbsup:
edit- you'll always get same amount of HR and LR but without average contrast scene you may or may not get a nicely balanced /exposed frame
This is where DP experience comes in...

 

[sbroock]

It means that , in average setting, average contrast scene, with average balance between highlights and shadows, you'll nicely balanced exposure i.e. same amount of headroom and legroom(?) off the 18% grey chart level.
Now you should hit wikipedia for the term definition of terms you are not familiar with in the above sentence:thumbsup:

And as the rating is for the sensor itself, variables to exposure involving shutter/aperture are not taken into account?

 

[Jacek Zakowicz]

SENSOR(!) ISO

SENSOR(!) ISO

And as the rating is for the sensor itself, variables to exposure involving shutter/aperture are not taken into account?

Yes it's the sensor only.
Remember it's not about the actual exposure(you'll get the shutter, aperture setting off your light meter reading off the 18% grey)
It's about the BALANCE of headroom and legroom being equal:smash:

 

[sbroock]

Yes it's the sensor only.
Remember it's not about the actual exposure(you'll get the shutter, aperture setting off your light meter reading off the 18% grey)
It's about the BALANCE of headroom and legroom being equal:smash:

Thanks -- got it.