Exposure control in a raw developer: misnomer?

Started Jan 30, 2013 | Discussions thread
OP dosdan Contributing Member • Posts: 505
Re: Exposure control in a raw developer: misnomer?

dosdan wrote:

As I understand it, the "Exposure Triangle" is composed of Scene Luminance, Shutter Speed, Aperture (or should that be "F-number"?). These 3 alone determine the number of photons captured by the sensor.

Yes, it should f-number.

Consider: a 100/F2 lens fully open has a much bigger aperture (diameter; area) than a 50/F2 lens. What determines the amount of light reaching the sensor is the f-number (the ratio of FL to effective aperture dia.) So, when fully open, a 100/F2 and 50/F2 lens both admit the same amount of light. Same with a 300/F4 and a 28/F2.8 lens, both closed down to ƒ/8. So swapping between two lenses (assuming the same transmission loss), set to the same f-number, should result in the same exposure.

("T-stop", instead of f-number, is used when the transmission loss is factored in.)

(f-number/f-ratio/f-stop is a ratio of ƒ (focal length) / entrance pupil dia. Just as ½ is bigger than ¼, so ƒ/2 is a bigger ratio, and for the same FL, a bigger area, than ƒ/4.)

So it should be:

The Exposure Triangle is: Scene Luminance, Shutter Speed, f-number (or T-stop, if you're pedantic).


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