As long as I can remember, I've been a combination of artist and nerd. Ignoring, for a moment, my teenage angst years where I did the exact opposite of what my parents wanted for me, I have always loved learning, researching, creating and learning even more about myself and the world around me. (My good friend Meghan called me the 'Book of Useless Information,' which I take as a huge compliment!)
This is why photography is the perfect hobby and skill for me. It combines creativity within specific constraints (which I love), and there is always something new to learn, to experiment with and to explore.
I've never taken a technical photography class, but the more I do and learn, the more I want to do and learn.
Watching a recent video on craft photography (which is, you guessed it, photographing crafts for sale and blogs), I became annoyed by the simplistic way that the presenter was discussing aperture. She started with the very typical 'a large aperture lets in more light and a small aperture lets in less light.' That's fine and is the basic concept, but here is where it went off the tracks for me… she says,' but just to confuse you, a small f-number equals a large aperture opening. It doesn't make sense, but that is how it works."
I don't know maybe it's that 'nerd' side coming out but actually, doll-face, it does make sense if you educate yourself on what that number represents.
That sounds callus, I know, but in the Information Age it is easy to dive in a little deeper so that you understand more about what you are doing and why. Or maybe my personality drives me to want to understand the way things work beyond the surface.
In the simplest terms, f-number is actually the denominator in a fraction. Let's look at two examples:
f/4 - aka: f over 4; aka: f divided by 4, or
f/22 - aka: f over 22
Jumping in the way-back machine for a moment to basic fractions, who can tell me which is bigger, 1/4 OR 1/22?
If you answered that 1/4 is bigger, you are right! It represents one quarter of one, where as 1/22 represents one twenty-second of one.
Aperture is the same… the fraction f/4 nets a number that is larger than f/22. (And to clarify, the number we are talking about is the actual diameter of the pupil inside the camera that controls how much light hits the sensor.)
Make sense? Because that is how it works. If you understand basic fractions, it is literally that simple.
So, rewriting our video explanation: a large aperture, which is represented by a low number - because it is the denominator in a fraction, lets in more light. And the opposite is true for a small aperture.
We can stop there, but my inner nerd calls out for more, like - what does f represent in the fraction?. (It's like a 3 year old sometimes, asking why? Why? WHY??)
Adult self: A large aperture, represented by a small number, means the pupil controlling how much light hits the camera sensor is open wide. A small aperture, represented by large number, means the pupil is smaller.
3 year old self: Why?
Adult self: Because the aperture, or f-number, is actually the denominator of a fraction.
3 year old self: Why?
Adult self: Well, because the actual diameter of the pupil opening can be different depending upon the focal length of the lens, so it makes more sense to represent the aperture as a relative number than an actual number since the relationship of light to a specific focal length doesn't change.
3 year old self: Why is that?
Adult self: In this case, a relative number is actually more useful (and as it turns out consistent) than the actual size of the opening.
3 year old self: what???
Adult self: OK, let me start from the beginning.
Aperture on a camera is represented by f-number (or f-stop).
As we mention above, this is actually the denominator of the fraction "F / f-number = Pupil Diameter".
'F' = Focal Length
"Pupil Diameter' = Actual pupil diameter in mm
'f-number' is actually the Focal Length divided by Diameter.
Here is an example:
- A lens with a focal length of 100 and an f-number of 4 gives you a pupil opening of 25mm.
So, the fraction is 100/4 = 25mm. On the camera, you would just see f/4.
- A lens at a focal length of 100 and an f-number of 2 gives you and opening of 50mm.
So, the fraction is 100/2 = 50mm. On the camera, you would just see f/2.
Again, we can see that f/4 gives you a smaller opening than f/2.
- But suppose you have a focal length of 200 and an f-number of 4… then you will have a pupil opening of 50mm. (So the fraction is 200/4 = 50mm.)
Theoretically, we could have all learned how to use the actual diameter of the pupil, but the fraction is actually a more consistent way to represent the relationship of focal length to pupil size.
And, you don't technically need to know the focal length or the actual pupil diameter, you just need to know the relationship of the f-stop.
Meaning that a number like f/11 gives you a smaller opening than f/2.
3 year old self: What is focal length?