D3X vs 5D2 - myth and reality

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

bobn2 wrote:

I think Emil and the others were measuring rather than
speculating , also. When one measurement disagrees with others,
it's not speculation to say its an outlier. It's possible it's
right and the others are wrong, but unless you can show the error in
their methods, most of us are likely to take the majority view

Honestly, I don't give a fig for their "measurements", nor for the view of "most of you", for my measurements are good enough for me, beside being consistent. As soon as I see a contradicting measurement (which is not the same as a "statement"), I am ready to revisit my ones.

Not exactly clear, actually. The top end of the DR of the sensor
will depend on which of the colour channels tops out first

I am measuring raw channels .

Thus different sensors
with different CFA characteristics will display their best DR with
different illuminants.

A basic problem with measuring the DR on specific images under specific illumination is, that that result is totally useless in other setting or under other illumination.

A basic problem with your method and all the
others is that in the end you are using the sensor to measure itself

I am using the data gained from the sensor to measure the sensor's chartacteristics. I don't understand your objection. Should I use data from a specification sheet to support the specification sheet, or what?

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

I am looking for raw files with saturated areas.

Good. Now I find this hard to square with your statement "It is not
necessary to have any high exposure when measuring the DR; only the
dark end is interesting."

I don't understand this problem (but really). I measure the saturation levels on any image created by the same model with the same ISO. Although it does happen, that some copies have different saturation levels, the deviation is always negligable from the perspective of dynamic range. (The deviations are important when determining if some patch really clipped ot not.)

Thus it is enough for me to find some other shots to measure the saturation levels; it is not relevant, that the actual images used in these demo are clipping or not.

Besides, all the above becomes irrelevant, when you regard that my demonstration used only the red channel, the saturation of which is very firm.

But that is a very different statement and says little about the DR.
The bottom end of the DR is the read noise, and in your measurement
that is swamped by the shot noise, which is about 2.5 stops higher
than the read noise

1. The DR is determined by noise . Not by "this noise" or "that noise" but simply be "noise".

2. You would have to show me hard proof before I accept that the shot noise is 2.5 times higher than the read noise in the range I used for the demo .

The bottom end of the DR ratio is set by what you think is the
minimum acceptable signal distinguishable from the read noise. If you
take it as at the read noise floor you get one figure. If you decide
you want it one stop above the read noise floor, your DR measurement
would be one stop less. So, if you had two cameras with one stop
difference measured to the noise floor, the difference would still be
one stop measured to one stop above the noise floor

I have not measured anything from the noise floor. I don't even have to know where the noise floor is. (In fact, I don't know that.)

Consequence is that differences in read noise will be masked by shot
noise

It is of no relevance whatsoever. Does the difference make one camera better than the other? (Beside the max. 1/3 EV difference I noted at the beginning?)

Sorry, Gabor, I just don't think your measurements support the
conclusions you make, they are quite consistent with the D3x have
somewhere around two stops more DR than the 5DII

I don't see this.

I think you are using a different definition of 'DR' to everyone else

I need to repeat it: I have not used the term DR in my demo . I used the terms "noise" and "intensity".

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