For what it's worth, one can actually see the effect of aperture stopping down
by examining the behaviour of one's eyes as the intensity of light alters.
Our eyes have auto aperture adjustment which is presumably designed to
limit damage to the retina in strong light, and to ensure better survival
against
predators n dim light.
Carefully think about what you actually see in very good light. You should find
that in central field, objects are in sharp focus right from nearby to
infinity,
because your iris has stopped down to f/64 or something like that.
Then do the same in dim light, and look at something about 3 metres ( 9 - 10
feet) distant and you should be able to detect that the DOF is quite shallow..
Because the iris of your eyes is wide open at F/1.4 or whatever it might be.
Cheers, Brian
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