Best DSLR or ILC for Night Sky Imaging?

Started Nov 8, 2017 | Questions thread
bclaff Veteran Member • Posts: 8,544
Re: Sony A7S

sharkmelley wrote:

bclaff wrote:

sharkmelley wrote:
... Imagine a camera where you have the choice between pixels of 4 microns or of 8 microns. The per pixel read noise in either case would be the same since they use the same readout technology...

This is probably an erroneous assumption.

To maintain the same Full Well Capacity (FWC) per unit area the pixels will have different capacitors and the noise from the pixels will not be the same.

Sure, I would expect the FWC per unit area to be maintained.

I was making the assumption (perhaps wrongly) that the accumulated charge from each pixel would go through the same ADC and so would suffer the same read noise.

I think this is a wrong assumption.
It's OK to assume the same downstream electronics (including the ADC) but most of the noise originates in the pixel; you're assuming that most of the noise is added by the downstream electronics, it is not.

Do you know what the effect might be on read noise of decreasing pixel size?

The smaller pixel requires less capacitance to hold the smaller FWC so less noise originates in the pixel. I can't provide an equation but it seems that per unit area smaller pixels do at least as well as larger ones, perhaps better. This is good news because otherwise there would be a significant barrier to increasing resolution.


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Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

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