Horizontal Heavens Observatory "...From  A Galaxy Far, Far Away"
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This page was last updated on 08/23/13.

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Photon Transfer Analysis of ST-10XME

Photon Transfer Curve of ST-10XME *click here for database

By conducting a Photon Transfer Analysis on my own ST-10XME I can be absolutely sure of my Full Well capacity (Saturation Point) as well as the noise characteristics of MY camera.  I emphasize this because the few of us who have conducted a PTC/DTC have discovered a WIDE range of Full Well capacities and varying quality of CCDs being sold to unknowing customers.  While lesser quality CCDs will perform/produce acceptable images, the parameters under which they perform optimally cannot be ignored and must be adjusted for.  Unknowingly imaging outside of the particular performance specs of your own camera sample (YES, your CCD is unique) can result in added noise and poor imaging performance.

As you can see from the SN:Noise Log-Log Chart below, my ST-10XME reaches Saturation/Full Well at 45,161 DN (adu) / 62,773e-.  Personally I was expecting something like 55,000adu that I see on FITS headers and the like.  BUT I was confused about such things and really didn't understand the difference between DN (digital or adu numbers) and e- (electrons) numbers.  Believe me, it is worth taking the time to learn the difference,...NOW.  The KAF Spec Sheet (this is a PDF file) for the KAF-3200ME says the KAF-3200ME saturates at 55,000e- and I just found that mine saturates ABOVE this at 62,773e- so I am pleased, to say the least.  The reason for knowing this number is that it now allows me/you to knowingly shoot FLAT frames at an appropriate level (~80% of saturation), in this case about 36,000adu as read on the histogram of CCDSoft/MaximDL (~50,000e-).  Doing this will give you maximum S/N for each subframe and allow you to stack larger numbers of subs without any noise penalty (signal building faster than the noise).

CAVEATS: 

  • While I discovered that my ST-10XME has a good Class 2 chip in it others have discovered by doing their own PTC/DTC that their dark noise showed the CCD to be out of spec (engineering grade sensor).
  • Another ST-10XME tested with a Saturation Point at just 41,000adu (this means that FLATS must be taken at lower values than mine as well such as 32800adu vs. 36,000adu).  This is still a good camera but appropriate adjustments have to made to use optimally (so do your own PTC/DTC and KNOW for sure).

(Below) This chart shows that my CCD is Shot Noise Limited (the best you can hope for) up to 71,750e- though the CCD saturates before that level (a good thing)

 

 

Vignetting of the ST-10XME CCD with NO TELESCOPE -  The chip is directly in front (maybe an inch) of the "flat litebox" and the only thing in the optical path is the attached CFW10 and a 1.25" Red filter.  And I was worried about how my telescope's vignette issues!  GEEZ!  FWIW, the dark bands to the right and at the bottom are the "overscan" areas.  These are fabricated/artificial pixels that record only the noise (offset) from each row/column on the CCD chip.  You can use the SBIG driver to turn them on/off as you need them for analysis.

Two hour test dark at room temperature (85F) too long to be looking for BAD pixels!  Looking for an area that does NOT misbehave so poorly...

20min dark at room temp -- Overscan Read Noise