Re: [ATM] Baffled Observatory Slit

[Mark Holm <mdholm@telerama.com>]

John Sherman wrote:

> Mel's shroud over your head also works wonders on very faint objects. What it does for me is, after I've had my eye to the eyepiece for a while, my eye becomes more dark-adapted. That is because the background in the eyepiece is darker than the nite sky (in my locations). Without having ever measured it, I assume my pupil has opened up more.

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
mdholm@telerama.com

_______________________________________________
ATM mailing list http://www.atmlist.net/