How to compare camera film ISO number to quantum efficiency?

[parinaz]

how Iso connect to potential barier??

 

[sophiecentaur]

Interesting... I never thought of that. I figured it was field-of-view related, like the bright sky tended to get included in the metering if I used my wide angle...

Most cameras provide Spot Metering so that you can avoid that problem but it is hard to use it any better than just using the auto setting and compensating later. It's something else to learn about and can be avoided if you are prepared to use bracketing shots. Also, if you shoot with Raw, you have a fair amount more tolerance than when using JPEG files. (But I now see I have made a similar point before on this rather elderly thread)

 

[davenn]

how ISO connect to potential barrier??

that was a bit difficult to understand what you are referring to ?? I will assume you are referring to the individual pixels on the sensor

The ISO setting doesn't affect that. All the ISO setting is, is an amplifier that takes the signal from the sensor and increases/decreases the signal level by changing the gain setting electronically.
Increasing the ISO = increasing the gain ... it amplifies signal + noise. This is why, particularly on lower end cameras, greatly increasing the ISO is pointless as the noise level becomes unacceptable even at moderate ISO settings 800 - 1600. High end DSLR cameras, like
the Canon 5D Mk3, 6D, Nikon D810 and the like have much higher quality sensors and amplifier electronics to reduce the noise level so that the ISO (gain) can be increased higher before noise become so much of a problem.Dave