The Recent F/stop Controversy

Started 1 month ago | Discussions thread
Re: Really?

Michael Fryd wrote:

Aaron801 wrote:

...

I think that I get what you're saying, that the amount of light that a sensor receives is totally different depending on what size it is and therefore the size of the opening of the lens in front of it. Of course f-stop is not the size of the opening but is a ratio... You need to do some math to figure out what the "equivalent aperture" is between different formats... but I'm OK with that.

Actually, at the same angle of view the "equivalent aperture" is the one with the same diameter. In other words it really is the same aperture; no math needed.

Actually, it's not. Not only because I am picky, but because lenses are not required to have circular apertures at all.

What is the diameter of the square?

What is the diameter of a triangle?

What is the diameter of a pentagon?

What is the diameter of a circle?

For of these questions have no answer. Did you know there are other more exotic apertures, some for example with dots? What about mirror lenses (usually fixed aperture). They don't even have a center.

You only need to do the math if you normalize everything to light per unit area (which is a great idea when shooting film).

Actually, no. I don't use film and would still have trouble normalizing a triangle and its newfound diameter. Or have to thing in terms of the amount of light as something related to each individual sensor size.

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