Shutter angles

[combatentropy]

I notice that film cameras have shutter angles in certain steps. Here they are, in degrees, with my guess for the reason for each. Please fill in my blanks and correct me where I'm wrong.

180 - standard shutter speed, 1/48 sec.
172.8 - at 24fps, yields 1/50 sec., for shots of TV screens in Europe
144 - at 24fps, yields 1/60 sec., for shots of TV screens in the U.S.
135 -
120 -
105 -
90 - half the standard shutter angle, so you can open 1 f-stop more
75 -
60 -
45 - one quarter the standard, so you can open 2 f-stops more
30
22.5 - one eighth the standard, so you can open 3 f-stops more
11.2 - one sixteenth the standard, so you can open 4 f-stops more

 

[Paris Remillard]

While those smaller shutter angles do allow/force you to open the iris more, they are typically used for how they render motion. ND filters are used to allow larger apertures in brighter light.

 

[combatentropy]

I see. Thank you. I was more wondering if there was any rhyme or reason to these particular numbers.

They seem to incur strange intervals. For example, a 30-degree shutter = 1/288 of a second. Are we trying to get around the flicker of a computer monitor or something?