2 Bin or not 2 Bin

[adamsp123]

Having got my Atik383L+ back ....sorted courtesy of FLO who did an excellent job of quickly replacing my faulty unit, I have been looking at some charts regarding arcsecond/pixel and what's best for DSO imaging.

Now it looks to me with a focal length of 1007mm and a pixel size of 5.4 microns that by going to 2X binning (10.8 pixel size) would give me 2 Arcsec/pixel ie about spot on for DSO work.

Am I right or have I missed something and therefore not binning would give better results?

Cheers Pete

[roundycat]

If your guiding and focusing is up to it then unbinned (or potentially oversampled image scale) is worth it for the extra resolution you will get. Less than 1"/pix is probably too small for UK skies but not necessarily. Provided you can get shot noise limited exposures so read noise is not a problem you will get better results going un-binned.

Dennis

[riklaunim]

I use SCT 8" and point to small targets like planetary nebulas. Bigger ones like M27 look nice at bin 2 with DSI III Pro and SCT reduced to f/6.3. Smaller like Saturn Nebula look better at bin 1 at f/10 (and probably even better at f/20 when I'll have a chance to try it).

Atik383L+ has smaller pixels, and more of them. Bin2 should give nice results and high sensitivity.

[adamsp123]

Thank you for the replies, I would, given some clear skies, do a test run on a suitable subject for binned and unbinned run to compare, could you advise on a test object?

I did do a run last night on M27 narrowband, the 2xbin at 8 mins gave me some good looking subs although I haven't processed them yet, I take it at 2xbin I am getting 4x the equivalent exposure than 1xbin?

cheers Pete

[MartinB]

Thank you for the replies, I would, given some clear skies, do a test run on a suitable subject for binned and unbinned run to compare, could you advise on a test object?

I did do a run last night on M27 narrowband, the 2xbin at 8 mins gave me some good looking subs although I haven't processed them yet, I take it at 2xbin I am getting 4x the equivalent exposure than 1xbin?

cheers Pete

The binned x2 will be x4 as bright but the shot noise will also be increased proportionately so, purely interms of shot noise your signal to noise wont have improved. Very roughly however, you will only have 1/4 of the read noise since this is (roughly) a fixed contribution whether reading 1 pixel or a binned group of 4. This means you can expose for a much shorter time to effectively eliminate the read noise. Also, since dynamic range is determined by full well depth divided by read noise your dynamic range potentially increases by 4. This is a very simplistic over view because the full account will all the ifs and buts is beyond me and would make turgid reading to the vast majority!

If you are going to compare binned and unbinned, expose the binned for 1/4 the time you expose the unbinned. One comment that people often make is that binned images have bloated stars, one reason behind this can be that people often over expose when binning and saturate their stars. Another is that you will definitely loose resolution if you are significantly undersampled.

Although you may loose some resolution the better dynamic range when binned may allow you to improve discrimination between different subtle shadings.

I will be very interested in your results.