How does the D3 achieve such high ISO?

Started Feb 17, 2008 | Discussions thread
Marianne Oelund Veteran Member • Posts: 7,788

My earlier calculations posted above were unfortunately based on certain Mk III data from Roger Clark's website which, as Emil pointed out, had not been updated with the correct value. In fairness, I have redone the analysis to reflect the true performance of the Mk III vs. the D3. The end comparison is the same - the D3 still leads - but the margin is considerably less than previously stated.

Sensor DR at ISO 200 illumination limit:
D3 full-scale e- count = 65,600 (Roger's number)
D3 read noise = 6 e- (my number, more conservative than Roger's)
Mk III full-scale e- count = 38,000 (Emil's number)
Mk III read noise = 4 e-
D3 sensor DR = 65,600/6 = 11,000 = 13.4 stops
Mk III sensor DR = 38,000/4 = 9,500 = 13.2 stops

Shot noise ratio:
Shot noise dominates at low ISO, or in light tones at higher ISO settings.

Above ISO 200, the same full-scale e- count ratio occurs (65,600/38,000 = 1.73). Thus Mk III shot noise at a given ISO is equivalent to D3 shot noise at that ISO multiplied by 1.73: Mk III ISO 200 == D3 ISO 350, Mk III ISO 800 == D3 ISO 1380, etc. This is equivalent to about a 0.8 stop advantage for the D3.

Read noise:

Read noise determines shadow noise, and affects dark, mid-dark, then medium tones as ISO settings are increased. What is the noise expressed in DN, which is what we actually see in the image?
For example, at a moderate sensitivity of ISO 800:
D3 full-scale e- count = 16,400
D3 read noise = 6 e-
Mk III full-scale e- count = 9,500
Mk III read noise = 4 e- (using an optimistic value; actual is a bit higher)
D3 read noise = 6/16,400 * 16,383 DN = 6 DN
Mk III read noise = 4/9,500 * 16,383 DN = 7 DN
Thus the D3's read noise component at the A/D converter output is
slightly lower than the Mk III's.

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