ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
bobn2
bobn2 Forum Pro • Posts: 61,712
Re: Basics of digital camera ISO

Architeuthis wrote:

#1. Sensor has always same amount of photoelectrons in a given pixel after identical exposure. (Sometimes the readout current can be at different size, when the sensor can be operated at two different supply voltages as e.g. is the case with the dual gain in the GH5s ???)

That isn't how 'dual gain' works. The 'conversion gain', which is the parameter being changed, is the inverse of the capacitance of the pixel input node (think about it C = q/V, so for a given input charge q, the output voltage V= q/C, i.e., the larger the capacitance, the smaller the output voltage. The dual gain feature builds an additional capacitor in each pixel, and switches it in at low ISOs to lower the pixel output voltage.

#3.: A/D converter has always the same range of input sensitivity (e.g. 0V-1V (according to bobn2 it is more likely around 1V than my intitial 5V guess))

This is an interesting observation. Rather than the provision of variable voltage gain, to produce the effect that Chris says is 'ISO' a much simpler expedient would be to simply reduce the ADC reference voltage (Fr information, almost invariably the 'fall scale' of an ADC is referred to an external or programmable reference voltage. There is a very good reason that cameras are not designed this way, but as far as Chris' story goes, it would be just as good as the VGA, actually better because there would be none of the amplifier noise that he supposes the VGA is adding.

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263, look deader.

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