Originally posted by jspi What is "One Stop"?
One stop later is the place where the bus slows down to a halt, again, to let people hop on or off.
Two stops is a bit further away, that place where the doors ...
Or should that be "One Stop" of -
what, precisely?
1 EV? Exposure stepping?
A camera lens, perhaps? - DEFINITION: In optics, the f-stop
of an optical system (such as a camera lens)
is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture").
So the f-stop is a
ratio! It just happens that sometimes the ratio has special values (you know which values). But f/6.3 is a valid f-stop too. Also f/10 is a valid f-stop too. It's just a number, the result of a division. Focal length / diameter. A ratio. It just happens that people got used to a sequence of special numbers for historic reasons and for practical reasons. Related to exposure.
Quote: Control, control, you must learn control!
Yoda said. “Feel the force!” Three parameters the exposure has. ISO, aperture, shutter speed.
First exercise, a Jedi mind trick: About ISO you shall forget. (hand waving down) That parameter - fixed. Aperture setting - fixed, as well. Now down the ladder you climb - of some special, known, memorized, shutter speeds. 1/4s -- 1/8s -- 1/15s -- 1/30s -- 1/60s -- 1/125s. Happens what? The exposure between those steps:
it halves ! Up the ladder - the exposure doubles. Those, the usual bus stops they are,
evenly spaced. +/- , [german: pi mal Daumen] Sort-of.
Second exercise: Keep ISO fixed. Keep shutter speed fixed. 1/125s. Now let's find some special numbers, ratios, that allow
halving of exposure at each step. You'd have to mechanically control the aperture, through turning a ring, obtaining smaller and smaller diameters of the entrance pupil of the lens. Take note of the diameters that give those evenly spaced exposure steps. It just happens that the sequence of numbers, obtained as a ratio (focal length/diameter), is that special series:
1 -- 1.4 -- 2 --2.8 -- 4 -- 5.6 -- 8 and so on.
Science, there is. Physics. And some magic pixie dust.
Last edited by CristiC; 05-13-2022 at 02:55 PM.
Reason: more pixie dust than attention there is