24mp in our future for d300 replacement?

Started May 26, 2012 | Discussions thread
bobn2
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Re: 24mp in our future for d300 replacement?
In reply to Antony John, May 28, 2012

Antony John wrote:

bobn2 wrote:
MichaelEchos wrote:> >

High MP used to affect high ISO performance,

not really, there was a lot of noise made that it did, but it was always a myth.
Bob

Interesting comment. As a larger sesel has a great signal and,

It depends on what you mean by a 'great signal'. Small pixels are more sensitive because they have higher conversion gain, thus they produce a larger voltage signal from the same amount of light. If you engineer a large pixel to have the same sensitivity, it saturates earlier and the sensor as a whole cannot collect as much light. So, the idea that a larger pixel generates a 'larger signal' is just not true, if you measure the output in volts (or amps) which is what is relevant when you wish to consider amplification noise. The small pixel needs no more voltage amplification, if it becomes smaller under strict scaling.

for a give technology, the noise will remain constant but the signal increases one would think the opposite.

Both the signal and read noise, measured in electrons, decrease, in proportion, so the pixel DR remains constant.

from what I've seen on DXOMark, the High ISO performance has remained constant as the sensel size has decreased - over the past few years (Nikon at least).

Interesting, eh?

Working backwards, the larger sesels should thus have improved Hi Iso sensitivity with a larger signal.

Your idea doesn't work forwards so why would it work backwards? If you got no loss shrinking pixels why would you get a gain making them bigger?

In fact, high ISO performance, taken as a whole, has improved as pixel size has reduced. That is because if you aggregate more pixels with the same DR you end up with more DR in aggregate.

Amp noise will also remain constant irrespective of the sesel size so again one would expect improved SNR performance with a larger sensel.

The 'amp noise' is a voltage noise and is input referred (i.e. appears like photoelectrons) through the charge-voltage conversion factor of the pixel, so since that is higher for a smaller pixel, the same voltage noise appears like less photon noise.

Just asking why this should not be the case

And I've told you.
--
Bob

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