Binning 1x1 vs 2x2

[Rodd]

Thought I would see if there was a visible difference between binning 1x1 vs 2x2 for a scope/camera system that shoots well below the local seeing.  My C11 Edge with the .7x reducer and STT-8300 at 1x1 binning has a resolution of .57 arcsec/pix--well below local seeing (3-4as/p).  Binned 2x2 the resolution is 1.14--probably still below seeing but more reasonable.  Anyway--here is the Crescent Nebula: 1 20 min Ha sub--no calibration or prcessing.  The subs were shot back to back with only a few seconds between them .  FWHM is about 2.5 for the 1x1 binning and 2.8 for the 2x2 binning--both not bad for the local seeing.  I remember seeing posts where the difference was not obvious in similar demonstrations.  I think the difference in this case is striking, and I will be binning my C11 Edge 2x2 unless I am blessed with exceptional seeing. First image is 1x1, second is 2x2.

[RuralBill]

Totally agree.

Bill

[ollypenrice]

I also totally agree. Never mind the FWHM comparison. (Is this a picture of stars or is it a picture of a nebula? The final appearance of stars depends far more on the skill of the image processor.) The nebula is deeper in the binned image and will take more processing before breaking down into noise. I know which I would rather set about processing. Give me the binned any day. 

Olly

[Rodd]

1 hour ago, ollypenrice said:

I also totally agree. Never mind the FWHM comparison. (Is this a picture of stars or is it a picture of a nebula? The final appearance of stars depends far more on the skill of the image processor.) The nebula is deeper in the binned image and will take more processing before breaking down into noise. I know which I would rather set about processing. Give me the binned any day. 

Olly

Olly--I have a question regarding guiding and binning.  I noticed that when I binned 2x2, my guide graph became very smooth--making me think guiding markedly improved.  However, the improvement I saw may simply be a by product of the scale of the guide graph, which I did not change--my guide graph is set to report in Pixels not arcsec.  Obviously, with big pixels (2x2 binning) the reported errors will be small, compared to guiding with small pixels (1x1), because an error of 1 big pixel is equivalent to more smaller pixels. The graph only reports number of pixels irrespective of size.  So while the graph indicated improved guiding, guiding actually stayed the same. Is this correct, or did my guiding really improve?

Thanks,

Rodd

[Stub Mandrel]

I'm going to try a binned version of my M27 to see what happens.

[Rodd]

23 minutes ago, Stub Mandrel said:

I'm going to try a binned version of my M27 to see what happens.

Good luck--remember, if you are not oversampled binning does not make sense (except perhaps for color filters over a 1x1 binned lum/Ha)

[Stub Mandrel]

Eos 450D with Skywatcher 150PL, I make it 1.57 arc seconds/pixel, so if my seeing was ~3-4 arcseconds the worth a try.

 

[Rodd]

24 minutes ago, Stub Mandrel said:

Eos 450D with Skywatcher 150PL, I make it 1.57 arc seconds/pixel, so if my seeing was ~3-4 arcseconds the worth a try.

 

Hmm....Not sure its a given.  Olly would know better.  1.57 is not that small.  I think you might be approaching a line where you really have to experiment and take a look.  My situation at .57 (with a reducer) was a no brainer for my seeing (even when its the best it can be). 

[Stub Mandrel]

OK, I've done the experiment. First is my original unbinned stack, second is the binned one. The first one has probably been a bit over-sharpened, I didn't sharpen the binned one and its much less noisy. These are only 32 30-second subs because it wasn't fully dark. What jumped out at me was that the binned version had much more colour in it from the start.

I'm editing this as side by side it is clear the unbinned version has more detail in the nebulosity - at least know not to bin!

[ollypenrice]

11 hours ago, Rodd said:

Olly--I have a question regarding guiding and binning.  I noticed that when I binned 2x2, my guide graph became very smooth--making me think guiding markedly improved.  However, the improvement I saw may simply be a by product of the scale of the guide graph, which I did not change--my guide graph is set to report in Pixels not arcsec.  Obviously, with big pixels (2x2 binning) the reported errors will be small, compared to guiding with small pixels (1x1), because an error of 1 big pixel is equivalent to more smaller pixels. The graph only reports number of pixels irrespective of size.  So while the graph indicated improved guiding, guiding actually stayed the same. Is this correct, or did my guiding really improve?

Thanks,

Rodd

Are you sure you bin the guide chip when you bin the main chip? I don't know your system but seem to think you have some kind of self guiding CCD?

If you do then the true guide trace will probably be much the same as at was unbinned because, as you say, the guide resolution has been reduced. When I first guided at 2.4 metres FL with an OAG I was horrified by the guide graph until I worked out that it was really indicating about 0.4 arcsecs.

I wouldn't regard 1.57 "PP as unrealistic. It would strike me as being a very nice DS resolution, in fact. I run at 1.8 in our TEC 140 and like the results a lot.

Olly

[Stub Mandrel]

Yes, I will stick with using the 450D unbinned.

[Gina]

Yes, I've often found with my MN190 and 460EX the seeing meant 2x2 was just as good as 1x1 and needed much less epxosure, of course.