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[quote name='Rainer' timestamp='1316858358' post='11810']

I tend to disagree on this one.



In my opinion, there is no such thing as an "equivalent ISO setting".

[/quote]

The you are just wrong, though. There definitely is such a thing as "equivalent ISO setting".



Like I pointed out above, ISO is not about the sensor's sensitivity, like it was with film. Then what is ISO about anymore? Nothing.

"ISO 400" says nothing anymore, it has become meaningless. Its only function now is the kind of equalize sensors of DIFFERENT sensitivity to sort of give the same exposure duration with equivalent focal lengths and same f-values, just to make things understandable for simple photographers.



Simplest it is to give an example with 4/3rds and FF, because the 2x crop factor is so easy to calculate with.



If you have a 12mp 4/3rds sensor (for instance from an E-30) and a 12mp FF sensor (for instance a D3).

Then the D3 sensor is about 4 times bigger in surface area. And each sensel about 4 times the surface size of that size of the E-30 sensel.

If you have an equivalent lens, say 100mm f4 on FF and 50mm f2 on 4/3rds, both lenses have a same size opening for the light to travel through. 50 / 2 = 25mm, 100 / 4 = 25mm.



So... same light intensity. Yet the 4/3rds sensor supposedly captures 4 times as much light (f2 vs f4)? It does not... Only reason it seems that way is that the signal amplification for the 4/3rds sensor is higher, to reach the same ISO setting.



So in order to capture the same amount of light in the same exposure duration, you have to equalize exposure.



To equalize exposure, you have to use EQUIVALENT ISO settings. Like ISO 100 for 4/3rds and ISO 400 for FF. It is just that way. Whether you agree with it or not.



Of course, you do not HAVE to use equivalent ISO settings at all, only when you have a need for the same exposure duration, for some reason. Or you want to really compare lens+body combinations.



So no matter how you twist or turn it, the 150mm f2.8 is either just a 150mm f2.8 on Nikon 1, or a FF equivalent of about 400mm f8. And if for whatever reason you want to drag ISO into it, do it correctly and look at what ISO now actually means. It only means an arbitrary extra amplification onto the amplification already applied to the signal, which differs from sensor to sensor.



Only two things that matter to the photo are the used opening (aperture) and the exposure time. Not whatever ISO setting that is used.

Only thing the ISO setting matter for is the noise levels, and the dynamic range which lowers when noise rises. But that is different for each camera, depending on sensor format, pixel density and sensor technology.