[Aavso-photometry] binning considerations

[arne]

David Trowbridge wrote:
> When doing photometry, is it okay to freely use 2x2 or 3x3 binning to
> achieve the desired image scale?
> 
>  
> 
> Where I live, the seeing is generally not better than 2 arcseconds I don't
> think. 
> 
>  
> 
> The photometry I've been doing so far has been with an SBIG ST-7E camera on
> a Takahashi FSQ-106 4" refractor which has been giving me 3.5
> arcseconds/pixel at f/5 or 2.2 arcseconds/pixel at f/8. 
> 
>  
> 
> Now I plan to upgrade to a larger scope for greater light grasp and a new
> camera for faster download times. I'm considering the Takahashi Mewlon 250
> and an ST-8XME camera. Using 1x1 binning this scope would give only 0.62
> arcsconds/pixel at f/12 and 0.80 at f/9.2. I think I'll need bigger pixels. 
> 
>  
> 
> Will it work just fine to use 2x2 or 3x3 binning? Or should I consider an
> ST-9 instead? 
> 
>  
> 
> Also, will going to a camera with microlensing have any detrimental effects
> on photometry measurements?
> 
>  
> 
> Are there any other issues I should be aware of?
> 
As Gary indicated, one of the big issues with binning is understanding
saturation effects.  If only one of the subpixels is saturated, the
output may *look* unsaturated, but may actually be contaminated.  Keep
your signal well below the saturation level.  I would stick with
2x2 as your maximum binning; 3x3 is pretty worrisome to me from
many aspects, especially dealing with saturation.  Note that, if you
bin, you also have to take flats and darks in the binned mode.

Having smaller native pixels means that you can take advantage of those
few good-seeing nights.  With your new setup, you will be properly
sampled for seeing around 2-3arcsec in the native unbinned mode,
which sounds pretty reasonable to me.  The ST9 is not available in
microlensed configuration, so has poorer blue response, and in
addition seems to be a noisier system all-around.  I'd stick
with the ST8.
Arne