[Aavso-photometry] Hot pixels and precision.

[Arne Henden]

Pedro,
   Is this a recent model ST-10 camera, or did you purchase
it "used" from someone else?  There were some changes about a year
ago regarding hot and unreliable pixels; contact SBIG for details.
   You can correct for the nonlinearity of antiblooming CCD.
The basic idea is to take a series of flats with fixed illumination
but increasing exposure time (the linearity set) to see how pixels
respond to light.  Plot the DN level vs. exposure time to get
a correction curve.  Up to some exposure level, you will usually
find the response to be linear.  You can keep the exposure below
that level and have reasonably good photometry.  Above that level,
you can apply the inverse of that curve to each pixel in your image
to flatten out the response.
Arne

Pedro Pastor wrote:
> I have recently acquired a ST-10 camera and I am in the process to get
> to know how it works.
> 
> The first thing I did notice is the great number of hot pixels it
> produces (at least compared with my previous MX916). 
> 
> I’ve tried to eliminate those hot pixels doing many dark frames and
> combining them via “Median combine” or “Sigma reject”. This produces a
> nice Master dark frame, BUT that’s not enough for suppressing the hot
> pixels from the “Light frames”.
> 
> If I would be doing “post card” CCD images I’d take many light frames
> and I’d Sigma combine them for eliminating hot pixels, BUT that’s not
> the case for photometry.
> 
> The point is: What would you recommend me to do? (Apart from changing
> the CCD camera ;-). Is there any other ST-10 user out there with similar
> problem?
> 
> On the other hand, I keep my MX916. One of the reasons for getting the
> ST-10 was the anti-blooming built-in system in the MX916. I think this
> system was affecting my measures but I still don't know how (the
> anti-blooming is only implemented in one specific direction). Could
> someone tell me how MX series anti-bloomming system affect the precision
> of the ADU measures? Is there any good strategy for compensating (or
> correcting) that effect?
> 
> 
> Thank you very much in advance.
> 
> Pedro
> 
> 
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