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Binning

marlin's picture
marlin
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Joined: 2010-08-31

What binning should I use for my new setup? I calculate 0.35 arcseconds per pixel in my Meade 16" SCT on an SBIG ST-10.  This will be for photometry.

Marlin Costello

binning
HQA's picture
HQA
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Joined: 2010-05-10

Hi Marlin,

Nice setup.  The Meade 16 works well, and the ST-10 is SBIG's most sensitive camera. What is your typical seeing?  The usual guideline is 2-3 pixels per fwhm.  This means if your seeing is 2arcsec, then you would want a pixel size somewhere around 0.7-1.0arcsec.  With your image scale, that would mean binning 2x2 or 3x3.

There are some caveats.  SBIG does not change the gain of the camera when binning, so you don't get the maximum potential from binning - that is, the analog/digital converter will still be at 2.5e-/ADU, and the maximum number of detected electrons will be 2.5 x 65536 = 164Ke-, even though 3x3 binning means you are summing 9 pixels, each capable of 77Ke- full well, or 693K electrons.  So when the ADC maxes out, each native pixel will only have ~1/4 full well.  You will get more dynamic range by running in native 1x1 binning, but you will lose by oversampling, so that the image size is bigger than necessary, it takes longer to download, and the readnoise per star will be higher.  I'd certainly run in native mode for exoplanet transits or any very high signal/noise application.

What some people do is use the 0.5 or 0.63 focal reducers to decrease the image scale so that you don't have to bin as much (or at all).  Since you already have the camera and telescope, adding a focal reducer is simple and should be considered.

Arne

Binning
marlin's picture
marlin
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Joined: 2010-08-31

Thanks, Arnie

     I neglected to mention I do have an installed 6.3 Meade focal reducer inserted into the focuser, an STF-S.  Further, right now I am doing photometry on variables but would like to switch over to exoplanets.  Seeing is 2- 3 arcseconds at 100 M elevation in a small city.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 aavso@aavso.org 617-354-0484