Why does squinting sharpen vision?

Point that a pin hole blocks surrounding light rays, but what 'high pass capacitor resistor roll off filter' does is block surrounding surrounding frequencies outside a band of frequency as too does a coil transfer magnetic energy at close proximity out of phase across winds of the wire called a low pass filter to remove the annoying unwanted electrical charge that would interfere.
Filtering is called "refining" , and such a process also occurs inside computers much alike a persons brain nervous system, so when a persons other eye sensors are shutdown or idled, much the same can be said of a computers' difficult memory and processor high load throughput , the computer does not need to multi task for threading if only one program is in operation and has more free memory to use as first in first serve until wait is called for another program.
Much the same for resource management and refinement would be similar in the brain because the eye has less spurious signals to collide with and can only use a limited number of sensors for perception.
Of Cameras, "Vignette blur" is a problem either long range or low quality lenses acquire because at long distance the light is generally a much lower power level into the lens, lenses themselves have light gathering specifications and often in long range camera lenses do not go down to 1.4 to 2.8 but often start at 5.8 to 8 in their aperture.
If you open the aperture (lower the number) there is more light coming in but the direct light is extremely low power and gets mixed with spurious light from non focus angles. It requires refining with more elements to block that much alike polarizing filters in specs or lenses.
It works more like a computer and propagation to look through a pinhole.