ZWO ASI533MC - Are these sub noise levels reasonable for this camera?

[abmwinnoch]

10 minutes ago, ONIKKINEN said:

Fewer pixels so the filesize is smaller naturally.

By the way ASI fitsview is not very useful for actual image analysis as it stretches the image with some arbitrary set value so you are not really seeing the raw data. Its better to view the image in something like Siril where you can make objective measurements on the pixel values/standard deviation/whatnot and try to make an educated guess on the sub. But ultimately i dont recommend viewing subs at all, just check their statistics when stacking (and maybe reject the worst ones) and only judge the final stack on quality.

Thank you- you've been very helpful.

[vlaiv]

3 hours ago, abmwinnoch said:

I've never been able to wrap my head around the concept of throwing away a third or a quarter of the camera resolution I've paid for and I also don't understand how the focal length of telescope matters? Surely a camera is telescope agnostic in that all it's 'seeing' is an analogue image from the focuser; how can it 'know' whether this image is coming from my 360mm WO or from a reduced 2888mm focal length of the C925? It's all just billions of photons landing on the sensor. Sorry despite having it explained to me on various fora over the past year or more, still don't get it. Thanks for trying though!

Here is simple analogy to help you understand what binning really is: Imagine you have just 4 pixels - 2x2 matrix and that is your whole image.

Instead of binning - imagine you do following - take each pixel and place it in image of its own. Now you've reduced resolution of each image but you have 4 independent images (no pixels repeat).

What happens if you stack 4 images? You get SNR improvement.

Same thing that happens when you stack subs - happens when you bin - only on pixel level.

Focal length is very important as it dictates the scale of object - which in turn spreads it over more or less pixels.

Say you have some galaxy and your aperture captures 1000 photons per exposure from that galaxy. Now, if you spread that galaxy image over 100 pixels - then each pixel will get on average 10 of those photons, but if you spread the light over 1000 pixels then each pixel will on average get 1 photon.

More you spread light - less of it will be recorded per pixel and lower signal means worse SNR (per that exposure).

3 hours ago, abmwinnoch said:

The 3x3 looks far noisier to me.

That is because you are looking at 1x1 scaled down. Zoom on it at 100% and then compare it with 3x3.

Scaling image down works a bit like binning (again, you are trading resolution for lack of noise)

Look at this:

this is same image - same copy - one viewed at 100% zoom and other scaled to 50% (or 33%) - one looks much smoother than the other - but it is the same level of noise in both (as they are same images).

[DSviewer]

Apologies is late and an odd question so I am guessing that the ZWO 266mc pro should require less exposure  time over the 294 correct and less noise.