To 2xbin or not to bin with a CCD?

[Martin-Devon]

As a newbie to imaging, so far for all of my imaging with HA, OIII & SII - I've used 2xbin mode on my Atik314. Is this the right thing to do though? Usually I focus on just one target for the night rather than skipping around, and can therefore commit around 1.5 hours on each of the 3 filters for that single target.

I see a lot of variation though between folks that regularly 2xbin their data capture versus those that don't bin at all. Presumably the 2xbin increases the signal (but lose some detail), whereas no binning will result in less signal but better definition - is this the way it works?

If you had 4-5 hours to spend on a target, across 3 filters, on a single good evening for imaging - would you 2xbin or not?

[ollypenrice]

I'd say don't bin except, on occasion, with colour. Some bin RGB but shoot unbinned L to make LRGB and this is not a bad idea at longer focal lengths, though I prefer never to bin.

In narrowband I'd say NO! You will get nasty blocky stars. NB is all about lovely tight structural detail, though it is very slow. Take half as many images and make them real keepers!

Olly

[BernieD]

Considering your equipment, 102mm F5.6 & Atik 314L gives you a resolution of 1.26 arcsec/pix. You need to get a very good sky to be able to get such detail on your picture. I would say you can bind 2x2 and get a 2.52 resolution that is close to the best resolution you will be able to achieve under normal conditions. My situation is different: AG8 200mm F3.6 and SBIGST200XM gives 2arcsec/pix unbinned. Therefore I always gets luminescence or Ha unbinned, RGB 2x2 binned: the luminescence gives you the details, RGB just adds the colors.

Thus if I had 4-5 hours exposing time (I dream of it), I'd go for: 3 / 3.5 h 1x1 Lum/Ha and the rest in RGB 2x2.

[ollypenrice]

Interesting from BernieD. I must say I never bin if combining Ha with RGB because of the difference in star sizes. These are always small in NB anyway (which is nice) but in RGB they are larger and in binned RGB larger still. So binning with NB has never worked for me.

Another thing that happened this spring involved trying to go deep on Ha for M106. I did lots in Bin 1 and tried Bin 2. It was awful, with big sqare stars. I threw all of it away. However, this is just one case so Bernie has clearly had a better time of it than I have. Just see what works for you, I guess.

Olly

[BernieD]

I think, but I might be wrong, that it depends on your setup: when too few pixels make up the image star, you get square looking stars. Consider the theoretical case where the resolution you can get with normal sky conditions is 2 arcsecs, and where your setup results in 2 arcsecs/pix, then stars will use as many pixels as you can get and result will be a round shape. If you increase the binning to 3x3, then you get a 6 arcsecs/pix and the stars will use only one or two pixels, it looks square... Now I almost always use Ha to image since my sky is heavily polluted, processing the image correctly (at least I try ;-)) allows to get good star size when you combine Ha & RGB...