I admit to being simple-minded. So, I think of it like this:
A tiny little man lives in my camera.
He knows what kind of film I have loaded. He understands ASA/ISO
numbers.
His job is to control the blinds that cover the window where the
film goes by.
If the lever on top of the camera is set to the "auto" position,
when the shutter button is pushed down and the mirror thingy flips
up, the little man jumps up and measures the amount of light
coming through.
Then he opens the blinds, and since he knows exactly what the film
wants, he closes them when enough light has been let through to
make the film happy-happy.
If I take a "spot" reading, or turn the little lever to "manual,"
then the little man watches the light coming through and measures
it.
He knows the light he is measuring comes to him through a wide-
open lens, so he looks up at the coupling pin, which tells him
what size hole in the lens I have chosen as the one that the
diaphragm doohickey will shut down to when I push the shutter
button.
The little man has a little chart (which he probably has memorized
anyway), and if I have set the lens number thingy at 8 and the
exposure reading was taken through a lens that has numbers all the
way down to 2 on that ring thing around it, he calculates that
since an 8 hole lets in 16 times less light than a 2 hole, the
blinds have to be open 16 times as long.
That's his job. My job is to let him do his job.
Walt
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
"I was raised in the country. I been living in the town.
I been in trouble ever since I set my suitcase down." -- Bob Dylan
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