Re: [ATM] Baffled Observatory Slit

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

Mark,

As I gather from Leibrock et al :
http://astro.umsystem.edu/atm/ARCHIVES/AUG99/msg00001.html
(the paper in question seems to have been taken off line - too bad!

the sensitivity does not depend on the amount of sensitized chemical (which 
is essentially constant and at maximum, at least in low light), but rather 
on the amount of "used", de-sensitized but not yet eliminated material. It 
is eliminated with a time constant of a few minutes, this governs the time 
of dark adaptation.

Nils Olof

> According to the things I've read on dark adaptation, your pupils open
> up fully rather quickly and at fairly high, by astronomer's standards,
> light levels.  The rest of dark adaptation involves a retuning of the
> receptors and neurons.  One of the major retuning effects, and one of
> the slowest, involves the retinal sensor cells actually synthesizing
> more of the photosensitive chemical that absorbs light and starts the
> process of converting the light signal into a nerve impulse.


> When this chemical absorbs light, it undergoes a chemical change that
> does not revert by itself.  The cell has to expend metabolic energy to
> convert it back to the active form.  In bright light, the amount of the
> active form is rather low, reducing the cell's sensitivity.  In dim
> light, the reconversion reactions catch up, making more of the sensitive
> form, so the cell's sensitivity goes up.
>
> -- 
> Mark Holm


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