Changing the paradigm

Started Nov 14, 2010 | Discussions thread
bobn2
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Re: ISO isn't just about sensor read noise
In reply to Joofa, Nov 15, 2010

Joofa wrote:

bobn2 wrote:

Joofa wrote:

The point I have been trying to make is that there is no 'game changing' technology being developed here as this paradigm is being advertised.

I disagree (well I would, wouldn't I, since I made the OP). the D7000 is the first camera with a flat ISO/read noise curve where the level of that curve is low enough to allow the kind of low light performance people demand.

I don't know enough about D7000 internal pipeline, but can't any camera have more or less a flat read noise if the analog gain component is disabled?

The reason for having variable analog gain is the use of an ADC which can only achieve 10 or 11 bits of DR. If you leave out the variable gain with an 11 effective bit ADC and shoot at a light level say six stops below sensor saturation level, you end up with five stops of DR in the output, which many think is unacceptable. Look at Emil's explanation here - he's done it very well so I don't have to repeat it:
http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/noise-p3a.html

Or better, don't use any analog or digital gain on the camera.

well, strictly there needs to be some analog gain just to match the sensor to the ADC, but the question is does it need to be variable, and the answer is no, if the ADC gives more DR than the sensor.

Just use software post-processing gain later. Right?

You're getting there.

If so, then it appears the 'game changing' aspect is just the low read noise.

Low and flat. the canons have low read noise (some of them lower than the D7000 at high ISO's) but the read noise/ISO setting curve is not flat.
Here's the 7D read noise

Compare with the D7000 read noise

If you set the 7D to 100 ISO and shot at a 6400 ISO equivalent exposure, you'd end up with 4.8 stops of DR, do the same with the D7000 end you end up with 7.9, and 3.1 stops of DR is worth worrying about. It's the point that you don't need to change the ISO setting to ensure high DR in low light that makes it an 'ISOless' camera, and that's a game changer.

Which is a figure of merit for sensors and can be discussed independently of this discussion.

there is not a single read noise figure for a sensor/capture system, it changes with ISO (usually). It is the impact of the flat read noise characteristic of the D7000 on the way you use the camera which is the point of this discussion.

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Bob

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