Quick question about binning

[Catanonia]

Really quick one regarding unbinned against 2 x binned

2x bin = 4 times the brightness / exposure of unbinned ??

Or there abouts ?

Is this true ?

[FraserClarke]

Yes -- with caveats

The signal from the pixels gets added together in the detector electronics, so the flux in all four (unbinned) pixels gets summed up. If the counts in each (unbinned) pixel are equal, then the binned pixel will have 4x the counts.

[shaunster]

2x bin does not get you anywhere near the figure of 4x the exposure of unbinned, sorry. From all the reading I have done and all the posts by Dennis (roundycat) I have read then you would be lucky to get about 1.5x increase in sensitivity.

[Catanonia]

2x bin does not get you anywhere near the figure of 4x the exposure of unbinned, sorry. From all the reading I have done and all the posts by Dennis (roundycat) I have read then you would be lucky to get about 1.5x increase in sensitivity.

thought as much reading the posts, just wanted to check with others.

Thanks

[FraserClarke]

2x binning gets you 4x brightness (i.e flux) -- which is equivalent in S:N terms as a 2x gain in exposure time (as, if you are source noise limited, S:N = sqrt(flux)). As soon as you go to stars, or anything with an uneven brightness distribution, that simple relationship falls down as you need to consider the sampling. Then you probably end up in the 1.5x gain region people get in practice.

[dph1nm]

To be honest, if your are not read-noise limited then there is little point in binning in hardware, as you can get the same effect by binning in software during your image processing.

I suppose if you are grossly oversampling the seeing then it is worth doing to it just to save on disk space.

NigelM