Date: Sat, 08 Apr 2006 08:35:28 -0400
From: bailyhill
References: <20060407181739.XGKI4002.centrmmtao06.cox.net
To: waltc
Cc: 

Hello;

What Walt says is correct here.  I have been bitten myself.  Before 
binning, you need to calculate your image scale in arc secs per pixel, 
and determine how many pixels per FWHM.  Arne's rule is "Do not go 

Clear Skies
Gary

From: waltc

   Do be very careful if you decide to bin for photometry.  It's too 
easy to fall
prey to the subtle problem where one pixel is saturated but the binned 
pixel is
not.  You are actuallly introducing a significant error into your 
photometry
because you are clipping off some of the photons and you can't even 
tell.  I
believe the difference in read noise between 1x1 and 2x2 is small so I 
don't
know that it is worth the risk.  You may actually lose some S/N by 
doing it.
One of the tricks used for millimag photometry is to oversample with 
very large
fwhm.

-Walt Cooney

>
> From: "Tom Krajci" <tom_krajci
> Date: 2006/04/07 Fri PM 12:31:13 EDT
> Date: 2006/04/07 Fri PM 12:31:13 EDT
>
> >From: "Chris Sauer" <chris
>
> >First off, I was amazed at how much the V filter attenuates the
> >light.  In 1 X 1 binning, I needed three minute subs to get decent 
ADU
> >counts on RS Leo itself.
>
> I looked at your image.  Considering the size of your star profiles 
(Full
bin 2x2.
> That may boost your SNR on faint stuff because there is less read 
noise.
> It's worth a comparison or two versus 1x1 binned images on the same 
evening.
> (And I'd be interested in hearing of your results.)
>
> >Also, what's the best way to perform the photometry?
>
> What software package do you have?  Most amateurs use software that 
does
> aperture photometry, not PSF fitting photometry.  However there is 
some
> software out there that does PSF fitting photometry.  If your star 
field is
> not crowded, then aperture photometry usually will satisfy the 
requirement.
>
>
> Tom Krajci
> Cloudcroft, New Mexico
> http://overton2.tamu.edu/aset/krajci/
>
>
>
>
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> _______________________________________________
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