DOF and Cropping take 2

Started Feb 11, 2014 | Discussions thread
awaldram Forum Pro • Posts: 13,246
Re: ISO, noise, exposure, and total light

And here it is on black and white

Read noise increases with ISO, because any noise added from the sensor readout before ISO amplification is then amplified by the ISO gain amplifier. A crude model of the variation of read noise with ISO is thus to assume independent pre- and post-amplification noise sources, that are combined as usual in quadrature:

R = (G R) + R

The two-stage amplification employed by Canon gives a bit more information as to what portion of the read noise can be attributed to different circuit components in its high-end cameras. Because of the second stage of amplification, one has separate information on how much of the read noise is due to noise in the main ISO amplification and how much is downstream from it in the secondary amplification and ADC. One sees from the table that the dominant noise at low ISO arises from the main ISO amplifier noise R, with a smaller contribution R from the components downstream from this amplifier and a negligible contribution from the sensor readout noise R. Lower noise amplifiers would improve low ISO read noise and result in higher dynamic range at low ISO.

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