The Phoblographer’s Exposure Triangle

The phoblographer website has published a great article regarding the exposure triangle. If you’re a beginner photographer, you should check it out. I have a slight problem with the phrasing regarding an aperture’s diameter (I think new users are slightly confused by the numbers) but it’s minor.

“…more you stop down your Aperture”
“(by increasing the F stop value/reducing the size of your lens’ opening)”

You don’t “stop down” a hole/aperture. A hole/aperture is bigger or smaller depending on its dimensions. A “stop” is a unit of measurement in the same way an inch is, but you don’t “inch down” a hole just as you don’t “stop down” a hole. You increase or decrease its diameter.

Aperture dimensions, e.g. f/5.6, are intuitive. The bigger the dimensions of the hole or the bigger the number = the bigger the hole (aperture).
f/2 = bigger number than f/5.6. Some will think to themselves, but “5.6 comes after 2!” and so it’s important readers understand what’s happening here too…

It is f/2 not “2” or “f2” but “f/2”. So let’s pretend “f” (your focal length) is 100mm to keep it simple:

f/2 = X (50mm)
f/5.6 = Y (17.8571428571mm)
aka 
100mm/2 = X 
100mm/5.6 = Y

You not given the apertures diameter as a simple value; you’re not given the true value of X or Y on the lens because the figures wouldn’t make any sense when switching lens types, so you’re given formulas. For example, if f = 21mm (i.e. a 21mm lens), then clearly 21mm/2 is completely different to 100mm/2.

This goes against what many educators say on the matter but aperture numbers are intuitive — X > Y.

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