Why calibration seems not working?

[Emanuele]

So, yesterday night I had to resort to using a 2" extension for my ML8300 because it seems my adapter is of the wrong distance.
but anyway, this is a test shot of 4x15min of Stephan's Quintet.
I shot 31 Dark frames at -20C and 15 min. Average combination and Average Sigma Clip rejection.

Seems to me that I am not calibrating anything. The noise level in the two frames is exactly the same. Am I missing something?

Thank you,
E.

[vicent_peris]

Hi Emanuele,

it's working, look at it carefully. At left, you have some hot pixels that are not present in the image at right. Do a blinking between both images and you will see it clearly.


Regards,
Vicent.

[Emanuele]

Thanks Vincent,

yes, I saw that, but I was expecting to get a noise free image, but that is not the case. Seems like it only removed outliers. The background noise is still there and thus the background is not smooth....

[vicent_peris]

That's photon noise. And that's why we invest hours and hours exposing our cameras. Calibration cannot correct photon noise from the object signal; the only solution is to collect more and more photons to have less uncertainty in signal quantity.

But hey, now you know that you have *only* the objects in your image, and that your data is instrumental artifact free. That's the nice advantage of digital versus film astrophotography. Isn't nice? 


V.

[vicent_peris]

That's photon noise. And that's why we invest hours and hours exposing our cameras. Calibration cannot correct photon noise from the object signal; the only solution is to collect more and more photons to have less uncertainty in signal quantity.

But hey, now you know that you have *only* the objects in your image, and that your data is instrumental artifact free. That's the great advantage of digital versus film astrophotography. Isn't nice? 


V.

[Emanuele]

Makes sense Vincent, thank you

This is my first image with a Mono CCD and first calibration. I always used Sony chips and never shot darks...

E.

[Nocturnal]

Sony chips still have shot noise.