D3X vs 5D2 - myth and reality

Started Jan 26, 2009 | Discussions thread
OP GaborSch Veteran Member • Posts: 7,203
Re: Measurements

bobn2 wrote:

The difference has been observed and demostrated by Emil and others,
so at the moment it would seem that your measurement is the outlier

As I am measuring this instead of speculating about it, I have no problem whatsoever.

Read noise, sure. As for DR (more on that later) this depends on full
scale count (not necessarily the same as saturation) which can be
different from channel to channel. What this means is that a camera's
DR does indeed depend on the actual illuminant - hence Iliah Borg's
magenta filter trick

Sorry, you are mixing up two different issues.

1. Calculating the actual intensity, relative to the saturation point: you need to know, when saturation occurs. I do know that (though sometimes some camera copies contradict that). Anyway, don't mix up the binary numerical range with teh saturation levels.

2. The composition of the illuminant. I have a magenta filter, which I use (extremely seldom) to increase the dynamic range of the camera , NOT of the sensor .



Let's put it another way, how do you discover the 'saturation points'?

I am looking for raw files with saturated areas.

I have not calculated the DR at all.

I find this difficult to square with your statement 'The result
proves, that the claim "two stops higher DR than the 5D2" is
ridiculous , like some other claims. In fact, the DR of the D3X is
max. 0.5 EV greater than that of the 5D2 at ISO 100, and at ISO 400
the 5D2 is already better.'

Back to my statement: the DR depends on the ISO, on the subject and on the actual illumination, AND on your acceptance of noise.

I am not saying how high the DR of this or that camera is. I am saying, that this or that camera creates a certain level of noise at a certail level of illumination (measured on the raw channel) . The difference between the D3X and the 5D2 is FAR from the two stops, even from one stop.

That's an SNR figure, not a DR. I've never been able to convince
myself that DxO's 18% grey noise value is a very useful metric

Not have I. I don't give a fig for how DxO measures the noise.

True, but it's always proportional to the ratio between full-scale
and read noise. All that happens is you might set your 'acceptable'
lower limit some amount above the noise floor


On many cameras 7EV from saturation is 6EV or more above the read
noise floor.
Shot noise will be about 3 stops greater than read noise at that level.
(Edit: I should have said 5 stops above read noise floor and shot
noise 2.5 stops above read noise)


The effect is slight, but at the same exposure the shot noise in 900
pixels of 5DII will be lower than 900 pixels of D3x

Sorry, this is far out of the range we are dealing with (the sample of 900 pixels is at -8.28 EV, barely over black clipping).

Anyway, create more suitable raw images and we can talk about it. Until then it is not worth of discussion.

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