The Purpose of Photography

There are as many reasons to take photographs are there are humans, and it's important to respect that.

There is photography for art, and there's photography for documentary purposes.

Finally, there's photography for nostalgia. (This is the marketing trope right here. That's how cameras are marketed!)

But it's not all bad. One of the most memorable parties that was ever thrown by me was in 2009. It all started with someone putting on a 20's and 30's playlist and it ended with everyone swing-dancing and jitterbugging the night away.

What makes it documentary is that someone grabbed my camera which was mounted with the 50mm prime and shot pictures almost continuously.

Every single one is out of focus (he was clearly drunk!) but it captures correctly the wild complex emotions of the evening (take that! your sharpness freaks!!) You can play it like a film (the man was seriously trigger-happy!)

It's "The Great Gatsby" as done for 2009 in film. Thank you, anonymous photographer!

A Quick Detour into Signal Amplification

Last time we talked about going to higher and higher ISO's. How does that work exactly?

Roughly put, the sensor at it's most basic level is a device that records whether or not a photon hit it, and if so, how many did? (We'll talk about color a little later.)

Basically when a bunch of photons hit the sensor element, it converts it into a buncha electrons. This charge is then amplified, and converted into a voltage. Measuring the voltage tells you how many photons must've hit the device in the first place.

The sensor is nothing more than a vast array of sensor elements, and the way it records colors is just by packing a tight array of red-green-blue sensors very close together, and then reverse-figuring out what the color must've been. Quite primitive in a certain way.

The key word in the last mumbo-jumbo is "amplification". A small trickle of electrons has to be converted into a flood of electrons, and then measured. This is where all the problems begin.

Firstly these sensors are all sitting on the same substrate of silicon (typically.) So a stray photon (or electron) could easily make its way onto the sensor even if it were not present originally. There are other quantum-mechanical effects that would make this happen even if things were "ideal".

So when you "amplify" the number of photons, you not only amplify the "real" photons that you wanted to but you also amplify the "noise" photons that you had no intention to.

Electrical engineers have a succint expression for this — When you amplify the signal, you also amplify the noise.

If you amplify enough, you will no longer be able to distinguish between the signal and the noise, or in plain words, your picture will be filled with garbage photons. It will look spotty like someone sprinkled random colors all over it.

There are ways to address this, of course, and that's what engineers are hired for but just "cranking the ISO" is not really a solution to your photography problems.

And that's why, muchachos y muchachas, you need to read this blog!

ISO, You Saw, We All Saw!

The last piece in the number of photons puzzle is the actual "photograph" itself.

A photograph is nothing more than a recording of photons. In the bad old days, you had film. These days you have a digital sensor.

The term ISO dates back to film. It has been co-opted in the modern digital world.

Effectively, it tells you the film's sensitivity to light. (In the modern world, digital sensor's sensitivity to light.)

The designers were well aware of the fact that light strikes the eye logarithmically so twice the ISO meant twice the speed.

Now digital sensors are basically the same but they allow going up to far higher ISO speeds than bad old film ever could.

Theoretically, going to higher and higher ISO's means that you are effectively increasing the "number of photons". However, practically it doesn't work that way.

That's for a future post though.

Stop, Just Stop!

Our eyes and ears have logarithmic responses. That is to say that we respond naturally to twice the light intensity, or twice the pitch of a sound, or twice the volume.

This explains the octave in music. The same goes for the eye.

A stop in photography represents a doubling of the light.

Memorize this.

Now recall the basic equation:

Luminous Energy ∝ L × r² × t

As a general rule, L is what it is. Whether you have a brightly lit garden, or a candlelit dinner, you have no control over it. What you can control however are r and t. So what would it take to double the light?

Well, you can either double the time, or increase the radius by √2.

If you understand this, you will understand the f-stop system which goes as 1.0, 1.4, 2, 2.8, 4, 5.6, etc. They are each increasing by exactly √2. (If you don't understand this statement, we will go into the f-stop stuff in gory detail later.)

Many many photographers do not grasp this. How a stop represents both increasing time, or dialing "down" the aperture. Is it time, or is it aperture?

The answer is both! You increase total light energy by letting more in.

Let there be light!

In the beginning, there was light.

Imagine a very bright source of light which is perfectly monochromatic (just one wavelength.)

Imagine you are in the room next door with a pinhole looking at it. (like the movie Psycho.)

The number of photons streaming past you is proportional to the intensity of the light (how "bright" it is), the size of the pinhole, and the length of time that you look.

Let's assume the pinhole is circular. (This will not really matter, as you will see later.)

In physics, instead of measuring the number of photons of a monochromatic source, it's simpler to measure their total energy because they are proportional. (E = h × ν.)

Illuminance is basically the amount of energy that is pumped out per unit area of the source.

(Aside: it's a little more complicated for light that is not all of the same color but let's ignore this point just for the time-being. We will return to this point later.)

Let L be the illuminance. If the pinhole is perfectly round and has radius r, and you look for time t.

Luminous Energy ∝ L × r² × t


That symbol (∝) which stands for "proportional" refers to the fact that the two quantities are related with a hidden constant — in this case, π, if you want to get all technical.

This should be very very intuitive. Double the illuminance (energy) pumped out, and well, you get double the energy (DUH!)

Double the time, and twice as many photons stream past.

Increase the radius, and the area increases as the radius-squared. This is the only tricky part.

Memorize this stuff. Everything that follows will be a direct consequence of this formula.

That pesky little "square" of the radius will play a disproportinate role in what follows. Take a careful note of that little bastard!

Is that all there is to it?

Photography is not an "art". It's half-science and half-art.

Photography is the great bitch of physics. Specifically, the physics of light at the visible spectrum.

More horseshit has been spewed on the subject of photography by people that don't understand basic physics than by all the horses in the world.

We are going to "inaugurate" this blog by walking through the basics. If you are a science-y type, you will enjoy it like a pig in (horse) shit. The rest will be mystified. No apologies will be tendered.

Photography is about capturing photons, and having the human mind make intelligible sense of the photons.

There. I've said it. That's all there is to it.

There are exactly two things here:

[1] recording the photons, and
[2] what the human mind does with the recorded photons.

Capturing the photons would be the science part. What the human mind interprets them to be (are they interesting? emotionally engaging? pleasing? annoying?, etc.) would be the art part.

These are solidly separate concerns, and since the blogger is the analytic type, we are going to engage both sides analytically (DUH!)

If you're not the science-y type, buckle your seatbelts. It's gonna be a (very) rough ride.

Welcome

Welcome to this blog!

The title is a pun. It's about my obsession with prime lenses, and as a mathematician, a joke about primes.

It's all about photography though. However, math will be involved.

The plan is to post anything and everything that interests me. Cheers!