Is it really the off-sensor ADC?

Started Jul 18, 2013 | Questions thread
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TTMartin
TTMartin Veteran Member • Posts: 7,304
Is it really the off-sensor ADC?

In the thread titled dynamic range confusion David Hull wrote:

texinwien wrote:

Sensor Dynamic Range vs. Camera Dynamic Range

This windowing of DR is occurring because the camera doesn't deliver the full DR that the sensor is capable of at base ISO; rather it is limited by the rest of the electronics -- the ISO amplifier and ADC. The sensor has a DR of about 14 stops, while the amp/ADC have a bit less than 12 stops DR. There are about two stops of extra dynamic range to be had in DSLR's that is currently being thrown away by limitations of components other than the sensor.

This appears to be exactly the case, a point I have been making for quite a while. From a sensor perspective what Canon is putting in there appears to be every bit as good as what Sony is making:

Nikon D600: QE=53%, Read Noise = 2.8e-, FWC=76231, DR~14.7 stops

Canon 6D: QE=50%, Read Noise 1.6 e-, FWC=76606, DR~15.5

Source: Bob's Sensorgen site (which is ultimately DxO, I guess)

. . .

People need to stop slamming the Canon sensor technology because it is actually pretty darn good. This also says the front end noise figure of ISO amp is pretty good as well. The demons are hiding in the rear end of it as Mr. Martinec points out. The sensor is not where bodies are buried in these things.

Thanks for putting this up, I had not seen it before – good stuff.

With the above showing that the 6D sensor is actually capable of producing 15.5 EV of DR it's time to again ask if it is really the off-sensor ADC?

It has been repeated ad nauseum that the off-sensor ADC is dumping tons of read noise in Canon RAW files.

If it were ADC inefficiencies, it should manifest itself as clipping not as read noise. Or in the off chance it was introducing read noise, that read noise should not decrease as ISO increases. Nor should the amount of read noise vary as much as it does from one Canon camera to another.

If some other component were introducing read noise prior to the ADC, then the read noise should not decrease as ISO increases.

None of the scenarios involving the off sensor ADC should manifest itself as increasing read noise, as you lower the ISO.

But, then where is that read noise coming from?

I've been ridiculed for my suggestion of where that tons of read noise comes from.

Is there anyone now willing to have a mature discussion on the subject?

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Canon EOS 6D
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