Sensor Tech Generational Improvments

Started 4 months ago | Discussions thread
Astrozoid
OP Astrozoid Contributing Member • Posts: 846
Re: Summary So Far

57even wrote:

I've never heard of flats removing DSNU. Are you sure about that?

My apologies. When you said flat frames I read it as dark frames.

No problem.

I'm a little unclear when you say "shorter exposures and higher ISO generate less of both." What is the "both" referring to?

Do you mean FPN and DSNU? Or Thermal signal?

DSNU, PRNU and also thermal signal.

How does a higher ISO result in less DSNU? I know how it helps with FPN.

DSNU is fixed pattern noise in the dark signal. It increases in proportion to dark signal so its proportional to time. Dark shot noise only increases as the square root. You reach a point (usually after many minutes) where DSNU dominates.

This is in addition to hot pixels and other nasties (requiring mapping or median filters).

Shorter exposure times mean smaller signal and dark signal signal = less DSNU (and PRNU) and of course, less dark signal.

Shorter exposures don't reduce thermal signal if you stack to equal a longer one.

If one is not stacking, wouldn't DNSU be proportional to the total integration time just as thermal signal is?

So, stacking 5 x 1min would equal the same amount of thermal signal and DSNU as 1 x 5min.

And the FPN in the DSUN would be 5x a single exposure.

At least that is what I think I understood before.

You said: "For stacking, you want all your noise sources to be random and Gaussian (or Poisson) so you get better results. Noise is reduced as the square root of the number of images in the stack."

I have understood this for a long time. I started stacking before DSLRs were even invented, back in the days of film. That was a lot of fun physically aligning micron sized stars, and even worse was keeping them aligned for printing or enhancing through copying. Can't say I miss that. Who was the first to do that? David Malin?

Jerry

You don't have to explain stacking reducing

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