[6-10] "On Bokeh"

I thought about bokeh last night; an analogy is a drop of wet ink that spreads on a piece of paper.

If the camera sees a small, highly intense source of light (e.g. headlight, street lamp) and it's surrounded by darkness, this dot could exceed the threshold of dynamic range; it attains a value of (255, 255, 255) "blowing out" the sensor. Its true intensity cannot be properly display on monitors. (But whether the detail is captured faithfully in RAW is an interesting question).

If we offset the focal plane, the small dot will spread its intensity across a larger area.

Hence, a blur (==bokeh).

Intensity will decrease (a drop of ink loses its strength as the blot increases in diameter; a green sharpie stain gets larger and less intense).

The blot also acquires the shape of a circle: it does not matter if it started as a line, a letter, or an oblong shape; the mere fact it is expanding in all directions means it will become more circular. The precise of the shape will be lost.

So bokeh is loss of detail due to circulation of distinct features (detail/information/frequency).

This seems basic, more questions:

• Why does bokeh become non-circular (e.g. cat's eye bokeh)
• Why does bokeh have irregularities and textures?
• Is bokeh generally a single color?
• What is the preferred amount of bokeh? Can there be too much?
• How can we mathematically determine bokeh (given lens/sensor) and can this be used for artistic effect (see Q4, above)?