[Aavso-photometry] binning considerations

[BailyHill at aol.com]

Hello David
 
No need to change your camera, binning is fine.  There is one thing to  watch 
for.  When you bin with the SBIG cameras, the readout in adu's is the  sum of 
4 pixels, if you bin 2x2 and obviously its the sum of 9 pixels if you bin  
3x3.  
 
So you can have a couple of saturated native pixels and not even know  it!!!! 
 This does not hurt too much, but when you try to do millimag  photometry, 
like when looking for GJ436 transits, where one needs all the  repeatability you 
can get, this invisible saturation will double or triple your  STd Dev of a 
check star.  I had this happen a few years ago, and it took  many tries before 
stumbling on to this.
 
So keep away from full well a little bit if you bin.  You can also do  a time 
series on a standard star and see what your std dev of the check star is  
over 30 images or so.  It should of course be ideally zero--never is.   An it 
represents what your REAL errors are contributing.  The 1/snr is only  one 
contributor to your errors, and unfortunately, its not the biggest one in  most 
cases.
 
Clear Skies
Gary



************************************** See what's free at http://www.aol.com.