Show us your subs...

[Hallingskies]

The subs from my ATIK 460 seem noisier than the ones from my uncooled SXV-H9, though I never used to go longer than 300s with that.  Below is a sample from a single unbinned and unprocessed 600 second sub of IC 443 taken with the Atik. Sky conditions were excellent at the time.

Is this a "normal" amount of "graininess"?   Just wondered what other folk's subs looked like...

[AbsolutelyN]

Being new to this I'm very curious. Here is same area of IC 443 taken last night - ZWO ASI1600MM Pro with ZWO HA filter (version ii). 600 seconds at unity gain (-20c).  

[Hallingskies]

Looks like my version (also taken last night) is a bit more stretched than yours.  When I tweak your version in PSP it looks about the same as mine wrt "graininess".  It'll be interesting to see if anyone "experienced" replies... 

The final effort didn't come out too bad with only 16 Ha subs (plus some RGB for the stars).

[wxsatuser]

Depends on how much you stretched it, you say no processing but you have stretched the image, otherwise it would be near black.
This is one PI STFed stretched 600sec sub from an Atik 383L, the more you stretch the grainier it will become.
The second image is a single PI histogramtransform stretch to the first vertical line.

[wxsatuser]

BTW this is the final image of 25x600secs.

[m.tweedy]

Here is a single 10 minute sub with an Atik 460EX mono with a 6Nm Ha filter. Cooled to -20

Its a fit file so cannot upload it. I will try later

 

[Guest]

Here is mine, 5MInute single sub with QHY163M

 

 

 

 

 

[AbsolutelyN]

20 hours ago, Hallingskies said:

The final effort didn't come out too bad with only 16 Ha subs (plus some RGB for the stars).

Excellent image ... also really enjoyed looking through your website, great work!

[Hallingskies]

13 minutes ago, AbsolutelyN said:

Excellent image ... also really enjoyed looking through your website, great work!

Thanks.  Just seen your wider field shot on the imaging forum - very good indeed!

On the subs front, looks like mine are not as bad as I thought l from what I've seen above.  I run my camera, filter wheel and dew heaters through a hub on the scope and I was wondering if the rat's nest of cabling was inducing some electrical interference that the camera was picking up.

[Hallingskies]

14 hours ago, wxsatuser said:

Depends on how much you stretched it, you say no processing but you have stretched the image, otherwise it would be near black.

You are right, of course - I use Astroart and that applies an auto-stretch to displayed images.  An unstretched image is very dark, as you say.  It is hard to compare background noise levels between images without (literally) a level playing field.  Unfortunately I have no idea what you mean by "single PI histogramtransform stretch to the first vertical line."  

Looking at my sub histograms though, there isn't any junk to left of the main "cliff" however - when I've had REALLY noisy images, there's loads of fuzzy stuff there.  Don't know enough about the theory to know if the two are related, however...

[wxsatuser]

1 hour ago, Hallingskies said:

You are right, of course - I use Astroart and that applies an auto-stretch to displayed images.  An unstretched image is very dark, as you say.  It is hard to compare background noise levels between images without (literally) a level playing field.  Unfortunately I have no idea what you mean by "single PI histogramtransform stretch to the first vertical line."  

Looking at my sub histograms though, there isn't any junk to left of the main "cliff" however - when I've had REALLY noisy images, there's loads of fuzzy stuff there.  Don't know enough about the theory to know if the two are related, however...

No stretch in PI, sub is and very black, histogram hard left.

One histogram transform stretch.

The more we stretch, this is three stretches and you can see the noise appear as spikes on the peak.

[Hallingskies]

Thanks.  I fully understand that  “stretching” an image brings up noise as well as signal.  It’s one of the first things I got to understand when I started astroimaging about 15 years ago.  What I don’t know is a way to measure or express a signal to noise ratio in a way that would allow consistent assessment of the noise in any given image. 

I realise the example I posted here is a bad one: IC 443 is a faint object even on a 600s sub, so the act of making it visible on a single shot will always bring up noise - it’s why we stack subs of course.  But how can you objectively assess noise levels in individual subframes?  How would you know if the background noise you see in any single sub is “natural” e.g. from haze or light pollution, or if it is down to some sort of camera fault?  Would darks or flats always address the latter if it the problem was of a random, non-uniform nature, e.g. electrical interference?