The logic behind the irrational f/stop numbers and the best deal on pizza

tim48v · Mar 5, 2025

Responding to questions from our Depth of Field video. We address the fundamental question: "why this sequence of numbers?" This relates to the definition of an f-stop and answers why f/16 is smaller than f/4.

hgernhardt · Mar 6, 2025

Once I understood the reciprocal nature of the f-stop, and then further understood that it dealt with powers of the square root of two because area, the number sequence made perfect sense. Now what I really find interesting is that the f-number doesn't always directly map to absolute light transmission (at least that's the explanation I got for t-stop versus f-stop usage in cinema)

loccdor · Mar 6, 2025

Thank you for the video.

The visual representation of the square root of 2 is something with a lot of explanatory power when looking out at the world and thinking about it.

Square roots were nothing but an abstract concept to me until I saw this unit triangle. The whole idea springs from this observation made by ancient people. The bottom side can be the horizon of the sea or flat land. The vertical side is a pole or a wall, or a string with a weight at the bottom. That is how we first derived this idea from our physical world. I will visit Samos, birthplace of Pythagoras, one of these years.

pentaxuser · Mar 6, 2025

Pythagoras? Didn't he invent that dangerous snake that named after him ?

pentaxuser
P.S. not a bad video

loccdor · Mar 6, 2025

Ah, that took me on a Greek etymological journey.

paul ron · Mar 6, 2025

thats the old plumbers trick for calculating the hypotenuse of an equilateral triangle....

1.414 x a side.

tim48v · Mar 14, 2025

hgernhardt said:
Once I understood the reciprocal nature of the f-stop, and then further understood that it dealt with powers of the square root of two because area, the number sequence made perfect sense. Now what I really find interesting is that the f-number doesn't always directly map to absolute light transmission (at least that's the explanation I got for t-stop versus f-stop usage in cinema)

That is true, there are other factors that affect light transmission such as number of elements, coatings etc. However, for most of us, the f/stop is close enough.

pbromaghin · Mar 14, 2025

I was taught that Pythagoras needed to easily re-mark fields after the annual Nile floods. He observed that the area of the 2 squares defined by the adjacent and opposite sides of the right triangle equaled the area of the square defined by the hypotenuse.

The logic behind the irrational f/stop numbers and the best deal on pizza

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