Best DSLR or ILC for Night Sky Imaging?

Started Nov 8, 2017 | Questions thread
Astrophotographer 10 Forum Pro • Posts: 13,017
Re: Sony A7S

rnclark wrote:

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.

Regards,

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.

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

Mark

I see no correlation of read noise with pixel size. Also you are describing sensor noise + downstream electronics noise, which I now call apparent read noise. When I see just "read noise," I assume just sensor.

Regarding large versus small pixels and apparent read noise per pixel when the read noise per pixel is the same, the number of the noise per unit area on the sensor is not the whole story. If you make prints or display where the subject is the same size, with more pixels the noise will appear smaller. So what would be a better metric would be noise per unit area of the final presented image.

Roger

A7r2 images downsampled to A7s size show the same level of noise so this would be correct.

There does seem to be a correlation with speed of digitisation and read noise though.

My astro CCDs have 2 digitisation speed settings. The slower one is rated to 50% less read noise than the faster (8X faster) digitisation setting.

Greg.

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