In article , Whisky-dave
wrote:

Sandman:
To create an equal image. With not enough light, the smaller
sensor will have to amplify the signal more and this creates more
noise. It's just something that most people don't think about.

Those that started taking pictures using film know this

No, because if you shot with a 35 mm camera, all "sensors" were the same size. It
wasn't an issue back then. It's only an issue now.

ISO 400 was ISO 400 regardless of camera used.

Eric Stevens:
The truth of the matter is that if you take a camera and scale
it either up or down, the lens f/value stays the same and the
level of illumination on the sensor stays the same. If the
sensitivity of the sensor has not changed then the invariant
level of illumination of the sensor means that exposure time
always remains the same.

Sandman:
But with the same f-stop, the smaller lens gets less light. So you
either need a larger f-stop or longer exposure time to match the
amount of light. This means you adjust the ISO down to the crop
factor square.

Crop factor is irrelivent. Not sure why you're getting so confused
by this.

Whoosh.

Eric Stevens:
Alternatively, if you have an invariant f/ value, an invariant
exposure time and an ivariant level of illumination of the
sensor then it follows that the ISO has remained the same. That
is, ISO value is not a function of sensor size.

Sandman:
Of course it isn't. But with the same exposure, sensor
amplification is a function of the sensor size, so while the ISO
number are similar, the sensor amplification is not. So, to
repeat: FF: 1/250, f5.6, ISO 800 MFT: 1/250, f5.6, ISO 800

so no differnce then.

Great way to snip out the other example that illustrates the difference, troll.

What you snipped:

FF: 1/250, f5.6, ISO 800
MFT: 1/250, f5.6, ISO 800

The above is the exact same *exposure*, but with different signal
amplification, the smaller sensor needs to amplify the signal more than the FF
sensor to present an equally bright image.

FF: 1/250, f5.6, ISO 800
MFT: 1/250, f2.8, ISO 200

The above is the same *amount of light* on the sensor, which creates as
identical image as possible using different sensor technologies. Also, you
adjust the ISO by the crop factor squared to match the signal amplification of
the larger sensor, so you will get very equivalent noise.

--
Sandman