09-25-2011, 09:21 AM
[quote name='wim' timestamp='1316907321' post='11824']
ISO settings are based on a quantified density of light, i.e., a quantity of light (photons if you like) per surface area, and therefore independent of sensor or any medium for that matter.
The size of the medium only influences things like granularity for printed images of the same size from different media sizes, and things like DR and SNR.
Furthermore, in order to expose an image properly, the EV was invented, which is based on this principle. EV 0 is defined as the light density required to expose an image properly at F/1, for 1 sec at ISO 100. This is totally independent of the medium, other than that it is a starting point. This is why we can use the same exposure meter for all cameras, regardless of medium size or FL, and why we get exactly the same value for exposure time at the same ISO and aperture, for the same lighting conditions.
Of course with sensors the base ISO may well be different than 100 ISO, however, that is a little besides the point from an exposure POV.
The same is really true for aperture and FL equivalencies. Although F/2 on a smaller sensor may be equivalent for actual DoF to a much smaller F-stop on a camera with a larger sensor, it still is F/2, and therefore "catches" the same amount of light per surface area as does any other lens at F/2. And this is also totally independent of the FL.
Sensor surface area only comes into play when calculating the total amount of light captured is calculated, as obviously this depends on the surface area. And FL doesn't come into the equation at all, because again, it is all about the light captured.
I think this is what Rainer and Markus are trying to say.
HTH, kind regards, Wim
[/quote]
I know, Wim. Thanks for you post.
Markus and Rainer appear to be missing that with film, its ISO rating was based on its grain size, it actually had to do with how sensitive the film was. With sensors that simply is not the case.
So where with film ISO was about how to correctly expose different films, with sensors it has lost that meaning totally. It is just a big equalizer with variable amounts of amplification of the actual exposure.
Equivalent ISO settings is just like talking about equivalent focal lengths. The lens does not BECOME 400mm, it still has a focal length of 150mm. It just achieves the same, so equivalent. Same with equivalent ISO settings. They do not BECOME a different ISO setting, they simply achieve the same thing.
ISO settings are based on a quantified density of light, i.e., a quantity of light (photons if you like) per surface area, and therefore independent of sensor or any medium for that matter.
The size of the medium only influences things like granularity for printed images of the same size from different media sizes, and things like DR and SNR.
Furthermore, in order to expose an image properly, the EV was invented, which is based on this principle. EV 0 is defined as the light density required to expose an image properly at F/1, for 1 sec at ISO 100. This is totally independent of the medium, other than that it is a starting point. This is why we can use the same exposure meter for all cameras, regardless of medium size or FL, and why we get exactly the same value for exposure time at the same ISO and aperture, for the same lighting conditions.
Of course with sensors the base ISO may well be different than 100 ISO, however, that is a little besides the point from an exposure POV.
The same is really true for aperture and FL equivalencies. Although F/2 on a smaller sensor may be equivalent for actual DoF to a much smaller F-stop on a camera with a larger sensor, it still is F/2, and therefore "catches" the same amount of light per surface area as does any other lens at F/2. And this is also totally independent of the FL.
Sensor surface area only comes into play when calculating the total amount of light captured is calculated, as obviously this depends on the surface area. And FL doesn't come into the equation at all, because again, it is all about the light captured.
I think this is what Rainer and Markus are trying to say.
HTH, kind regards, Wim
[/quote]
I know, Wim. Thanks for you post.
Markus and Rainer appear to be missing that with film, its ISO rating was based on its grain size, it actually had to do with how sensitive the film was. With sensors that simply is not the case.
So where with film ISO was about how to correctly expose different films, with sensors it has lost that meaning totally. It is just a big equalizer with variable amounts of amplification of the actual exposure.
Equivalent ISO settings is just like talking about equivalent focal lengths. The lens does not BECOME 400mm, it still has a focal length of 150mm. It just achieves the same, so equivalent. Same with equivalent ISO settings. They do not BECOME a different ISO setting, they simply achieve the same thing.