70D Dynamic Range is actually great, despite what DXOMark says

Started Jan 21, 2014 | Discussions thread
David Hull
David Hull Veteran Member • Posts: 6,388
Re: 70D Dynamic Range is actually great, despite what DXOMark says

Just another Canon shooter wrote:

David Hull wrote:

Just another Canon shooter wrote:

David Hull wrote:

It is interesting that looking at the SensorGen data from Bob's site, it shows that the actual sensor in the Canon cameras is pretty good in terms of read noise -- even better than Sony by a bit. IMO, Canon fouls it up in their circuitry down the line.

? The data there is derived from DXO, and shows that Canon's sensor have pretty bad read noise at base ISO.

Yes, I know where it comes from. Take a look at it again keeping in mind how the camera is architected. The DR of the sensor itself is log2(FWC/MinReadNoise). That is right on the front page of the site.

In the case of Canon, to see the read noise of the sensor itself, you need to get to the point where the noise figure of the back stage electronics no longer influences the measurement. To do this you need to turn the gain up so the noise from the sensor swamps out this back end noise. Take a look at the read noise on the 5DIII at 12800 (for example). Here you see a value of 2.4 e-. At this point you are seeing the actual read noise of the sensor itself with little influence from their noisy converter. In the case of Canon at ISO 100, you are not seeing sensor read noise at all, you are looking at the noise of the read out electronics. The 5DIII sensor is providing Log2(67531/2.4)=14.7 stops of DR. The 6D is even better at 15.5 stops.

Compare this to the D800 which shows 2.7 e- (in this case measured at minimum gain) for a DR=14.07 stops. Canon actually DOES make excellent sensors and has been doing so for some 10 years. They just need to fix the rest of it.

This is a really weird view of the data. You think that you can separate the read noise of the sensor from the read noise of the circuit, whatever those two mean? You are just saying that at high ISO, the two sensors look similar but we knew that.

In any case, at base ISO, the read noise is much worse.

It's not weird at all, if you know anything about the electrical design of systems, it makes absolute sense.  At base ISO, the read noise of the sensor in a Canon camera just about the same as that of a Sony, < 3 e-.  This is clear from the DxO data if you know what you know how to read it.  The fact that the read noise goes up at low gain (ISO) settings tells you that the noise is not coming from the sensor but from something in the back end.  It is the system implementation that Canon needs to change, their sensors are pretty darn good as evidenced by the DxO measurements.

You are correct that the system read noise is higher at lower ISO but that is because the sensor noise is no longer the dominant factor.

So here is a question for you:  As you say, the effective system noise (camera noise, if you will) is higher at ISO 100, so tell me how Canon would fix it.  in other words, based on the DxO data and the Sensorgen information based on it, what part of the Canon architecture needs to be improved?

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