After watching
this video, I was curious to see how the graphs would look like if I would use the full-well capacity of the entire sensor instead of ISO on the DR graphs.
With same-size sensors, there should be no difference. The difference appears when comparing sensors of different sizes: at the same ISO, the smaller sensor would get less light (fewer photons). Imagine you put your 50mm lens on 5D3, then on 60D, and take a test picture at ISO 200 1/100 f/4 on both cameras (just an example). You will get 2 identically exposed pictures (of course, with different framing). But on the 60D, some of the light will end up outside the sensor.
You may think: what would happen if you would concentrate the image to fit the smaller sensor? (that is, imagine you use some sort of adapter on the 60D, so you get the same framing as with the 5D3). In this case, both sensors would receive the same amount of light, correct?
So, let's compare how the sensors would behave with such an adapter, in the ideal case (think of a hypothetical Metabones 0.63x for the APS-C Canon, if one would exist). That's what the following graphs will show - how good the sensor technology is, regardless of sensor size.
In the first graph, you can see the 5D3 and the 60D are just as good. That is, if you would use a 80mm/2.8 lens on 5D3 and a 50mm/1.8 on 60D, you would get the same results (same framing, same low-light performance at high ISOs). The 6D is clearly better (about 0.5 stops) and the old 5D shows its age.
Second graph (sensorgen data) shows a few more Canons. The surprise here is the S100 compact - it's sensor is really good.
Note: the X axis in my graphs shows the total number of photons that should fall on the sensor in order to saturate it (assuming perfectly uniform brightness). It's reversed, so the graphs are similar to the previous ones (which have ISO on the X axis). However, I don't know how many photons correspond to what ISO (but it's easy to do the math).
Third graph (also sensorgen data) shows that GH4, Nikon 1 V2 and 6D have similar sensor technology. Sony A7S curve is a little weird - probably outliers in sensorgen data, or some sort of noise reduction, can't tell (if you have one, I'd like to see some test images).
From the isoless sensors, no big surprises: Nikon D5300, Pentax K5 and GH4 are pretty simlar; with a hypothetical Metabones adapter, they might have a small edge over the larger D800/D810. Also, the Olympus E-M1 is worth checking.
Caveat: the Metabones adapter doesn't quite convert your M4/3 camera into full frame. My graphs shows the ideal performance of such hypothetical adapter, if one would exist. So don't rush to sell your 6D for a Oly E-M1 + Metabones for astro
If you have used a Metabones adapter, feel free to confirm or debunk this theory.
