Re: [APML] Equivalent ISO of an ST10E CCD

[Jerry Lodriguss <jml@astropix.com>]

Hi Loke,

Ok, so if you make an exposure on a CCD camera, like the ST-10E and then 
you open the data file in a program like Photoshop (assuming you can save 
it in a format that PS can read or have a FITS plugin), and you put the 
cursor on the gray card in the image, what will the pixel values read?

Is it possible to do this?

Jerry


At 10:05 PM 4/5/2002 -0800, you wrote:
>Jerry,
>
>         Covington's latest version of "Astrophotography for the Amateur"
>answers this well on page 248. Basically, the speed of a CCD imager
>depends on how much of the CCD well you would like to fill. If for
>example you filled the lower bits of the well, then the CCD imager is
>liken to a very high speed film such as 1600 ISO. If you are willing to
>expose longer to further fill the well, the speed might be effectively
>100ASA. Filling the well further results in better SNR, remember the
>well depth of the KAF3200 has 12-12.8 bits of dynamic range. If our
>signal has 6 bits of dynamic range, we could fill the lower 6 bits of
>the well and be reasonably fine. But in this case the faintest parts of
>the image would be sitting at the noise level. However, if we were to
>expose longer, the 6 bits of dynamic range of the image might sit at the
>upper 12 bits of the well. In this case, the faintest parts of the image
>is 6 bits above the noise. So in summary, a CCD is both like a very fast
>film AND like a very slow film. Interestingly the noise is so low that
>if you were to treat the CCD as fast film, i.e. short exposures, the
>noise level is usually already much better than 100ASA film grain noise.
>I say this w/o proof.
>
>         The explanation above is a bit simplistic but mostly correct. Usually
>noise is also a factor of exposure length etc.
>
>Loke
>
>
>
>Jerry Lodriguss wrote:
> >
> > Ok, here we go again.
> >
> > It seems like a simple question:
> >
> > What is the equivalent ISO of an ST10E CCD camera.
> >
> > If it is not, in fact, a simple question, please formulate a simple answer
> > to explain it. <G>
> >
> > If I hook up an ST10E to a camera lens and take an exposure of a gray card
> > in the sunshine, what exposure would I need in terms of exposure length at
> > a given f/stop or correctly record the gray card?
> >
> > Simple, see? <G>
> >
> > Jerry
> > Photoshop for Astrophotography Book:
> > http://www.astropix.com/APBOOK/0_PROMO/PROMO.HTM
> >
> > Astrophotography, Tips and Techniques
> > for Digital Enhancement in Photoshop:
> > http://www.astropix.com
> >
> > --  APML Archives at <http://astro.umsystem.edu/apml/>  ---
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Photoshop for Astrophotography Book:
http://www.astropix.com/APBOOK/0_PROMO/PROMO.HTM

Astrophotography, Tips and Techniques
for Digital Enhancement in Photoshop:
http://www.astropix.com

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