Originally posted by Simen1 I just disagree in using equivalent ISO in comparisons. When some sensors have larger well depth then others then it just means they have larger pixels. Max charge per unit area is usually not that different between sensors.
In your hurry to disagree, you probably miss the whole point.
The well depth of the D800/E is 2200 e-/µm^2,
the well depth of the D810 is 3300 e-/µm^2.
[source:
Sensorgen.info data for Nikon D810 which in turn is a better look at DxO and its individual measurements -- except for older entries which are typically broken (show false data).]
That is considerably (50%) more and you need a lower iso setting to make proper use of it (to not underexpose). Therefore, comparing both cameras (or D810 and 645Z) at iso 100 is a bad way to compare their capabilities.
My way of doing sensor-size independent analysis did cope with that fully though.
Originally posted by blende8 How do you establish/calculate this?
...
And this is bad because ...?
Equivalent iso is defined by many sources, e.g.,
LumoLabs -- Camera Equivalence -- Whitepaper Equivalent base iso is established by first measuring a camera's true
base iso, e.g., using DxO measurement called "ISO sensitivity" (e.g.
Nikon D810 : Measurements - DxOMark ). For the D810, it yields ISO 47.
And then scaling it with crop^2 to arrive at the 35mm-
equivalent base iso.
Assuming equal quantum efficiency,
equivalent base iso is a direct measure of the sensor's overall (total) well capacity. The nice thing is that this is all one needs to know about the intricate ISO norm which defines camera sensitivity.
However, older sensors have smaller quantum efficiency, a fact which I ignored here for the sake of simplicity. In current age, all CMOS sensors, incl. Canon, are between 50% and 65% Q.E (more typically, between 55-60%). To avoid the effect of Q.E., you may want to use SNR at
base ISO instead (D810: 46.3 "DxO"-dB). But IMHO, just using the value of 35mm-
equivalent base ISO instead is good enough. These days, Q.E. is improving slowly only.
> "
And this is bad because"
This is bad because it means that the maximum SNR the camera can produce is rather limited (37.5 dB for the RX100m4). This means less clean (10dB less) images although physics would allow for better even for a small sensor.
P.S.
Anecdotical comment ... the RX100m3/4 has an in-camera app (badly named "Smooth Reflection") which allows to stack a (large) number of shots in-camera and in RAW (tripod required) which nicely simulates very low 35mm-equivalent base ISO which can become as small as ISO 2.3 (takes between a few seconds and 4 minutes to produce). Loading such a RAW in Lightroom is jaw-dropping