vlaiv

On 2.2.2016. at 14:45, dph1nm said:

The advantage of hardware binning is that you only get one dose of read noise per binned pixel, whereas e.g. with 2x2 binning you would have four doses of read noise in the unbinned image covering the same area of sky. So the read noise contribution per square arcsec goes down. With software binning you always have the four doses of read noise whatever you do. This is the only real reason professional observatories hardware bin their cameras - mostly for spectroscopy I think, although it is sometimes possible to do it for imaging.

NigelM

This implies that even in sky noise dominated scenario there will be difference between hardware and software bin, maybe not significant one, but still, even in this case hardware bin will be better than software. Only when there is no read noise they are the same.

Vladimir

5 hours ago, dph1nm said:

If your pixels are sky noise limited then software or hardware binning should give the same effect. If you have a significant read noise contribution then hardware binning is best.

NigelM

p.s. if you are going to software bin a DSLR it needs to be done before debayering the data.

Can you elaborate on this one? Noise is noise, no matter which source it comes from (sky flux poisson process or read noise or thermal noise), it may have different statistical characteristics, but in general it will be random unwanted addition to signal.

My view on things including original question is as follows:

Prefer mosaic + software binning (of stacked and stitched mosaic) over focal reducer (at least over any reducer that has not been specially designed for particular scope and of highest quality).

Pros of mosaic + software binning:

Smaller FOV to work with - less off axis aberrations of any kind (coma, astigmatism, field curvature) which are usually amplified by focal reducer.

Making mosaic in general does not require much more time to achieve target SNR (not really true due to read noise, but close enough). For example: you consider to take 16 subs over target area. In case of mosaic (2x2) you would use 4 subs for each mosaic segment. 16 subs would give you x4 SNR after stacking, while for other case: 4 subs per segment give you x2 SNR reduction for segment, and then you bin 4 segments (mathematically it is equivalent of stacking 4 subs) - x2 SNR increase again - 2x2 = x4 SNR, same as in first case. SNR has quadratic dependence, but so does area.

Here is my best of 2015.

All images taken with SW 130/900 newton and qhy5L-IIc on eq2 mount (SER recording, AS2! stacking, Registax wavelets, iMerge for moon mosaic)