How Your Camera Works – Photography Basics

Yesterday’s topic was:  The Exposure Triangle

Before we dive too deep into other subjects, I thought it best to explaining how your camera works. While not all the mechanics are the same for DSLR, smartphones, mirrorless, drones, etc… the principles are the same.

We’ll use this DSLR image for reference:

How Your Camera Works

How Your Camera Works

First, there is light. Let’s say it is coming from the sun and it hits our demonstration bunny here. Next, the light bounces off that bunny (she’s a tough bunny) and scatters in every direction.

Next, some of that scattering light comes in through our lens. The lens will have a number of elements, some made of glass and sometimes some made of acrylic or other materials. All these elements (think of them as type of lenses, like a contact lens) help to focus the light. A focus ring on a lens, as well as the auto-focus capabilities of the camera, will move one or more elements front to back ever so slightly in order to achieve focus. Think here of using a magnifying glass to get something into focus.

As light comes into the camera it is flipped vertically because of the convex shape used to concentrate the light into the sensor area (think of looking at your reflection on the inside part of a spoon). You’re now taking a foot tall bunny and shrinking it down to the size of the sensor. Poor bunny.


How Your Camera Works

Detour For DSLRs

Before the light passes out of the lens and into the camera body, it goes through the Aperture (explained next week) which, as you read yesterday, reduces the amount of light passing through to increase Depth Of Field. It then hits the reflex mirror (DSLR stands for Digital Single Lens Reflex, meaning it only has one lens and a reflex mirror that pops out of the way) and bounces up.

How Your Camera Works

Next, it passes through the focus screen. To put it mildly, different cameras are different. On average, the focus screen is a transparent screen often with an overlay showing actual focus points and other stuff overlayed in your viewfinder. This screen is the same distance away from the mirror as the sensor and this is the main reason the SLR became so useful. There was not a need to keep film out of the way, focus, put film in, expose, remove film as in the days of large format cameras (those ones with the big bellows and Ansel Adams come to mind).

Let Me See The Light

After passing through the focus screen, the light will bounce around the pentaprism (crudely drawn in this diagram; here’s a better version on Wikipedia) which will flip the image the correct way for presentation at the eyepiece. Tada! Some cameras will have a light meter above the eyepiece, reflected with a transparent mirror. Other cameras will have the light meter behind the main mirror, which is also semi-transparent. Don’t get too hung up on where yours is.

Now For Some Action

When you press the shutter release (or ‘button’ as a lot of people call it) your camera locks in the focus and light metering settings before flipping up the mirror. As later explained in the Shutter Speed post, it then activates the shutter (and closes down the Aperture to the appropriate size) to let light hit the sensor, which has had its sensitivity set by the chosen ISO. The shutter closes, the mirror drops back down. Below we have the shutter in action.

How Your Camera Works

What About My Smartphone, Mirrorless, Drone Or Action Camera?

The biggest difference between all the cameras listed above and a DSLR is the lack of all the stuff to bounce the light. They look, more or less, like this.

Most of the cameras listed above have a fixed aperture. Other than that, the light still comes in and gets flipped but now the sensor is hooked to the screen on the back (except for drones and some action cameras) and the software flips it back around so you can see it.

In smartphones, action cameras, drones and some mirrorless cameras, there is no physical shutter to block light. Instead the camera scans the sensor very quickly to simulate a shutter. Sometimes it doesn’t scan fast enough if something is moving very fast, which is why you get images like this iPhone shot:

Pretty funky, huh? That doesn’t happen with DSLRs.

More On The Actions

How Your Camera Works
Blue Morpho Butterfly (Morpho peleides), Costa Rica

Most cameras come to life when you press the shutter release half way down. At that point auto-focus (if engaged) and light metering become active. These two functions control most of the camera when in Auto and Program mode. Shutter and Aperture modes follow suit and we’ll cover these modes next week as well. If a lens has vibration reduction or image stabilization, it will turn on as well.

After light hits the sensor and the image is captured, the information drops into a buffer. A buffer is a holding pen for information. Inside the camera are one, two or more processors, just like in your computer and, eventually, toaster. The processors need a bit of time to crunch the raw information from all those millions of pixel sensors. The buffer allows a space for incoming images to hold up until the processors can work. then it will dump the images onto your memory card. Light goes:

Subject->Lens->Sensor->Processor->Buffer->Memory Card

Think of your buffer as those long, long, swerving holding pens….errr….lines at Disneyland. If more people come into the line than the ride can load at one time, eventually the line gets full. Pretend no one else is let in when the line is full. That’s what happens with the buffer.

Shooting at eight frames a second will fill a buffer and the shooting speed of the camera will slow to the point where a new picture can only be taken when another has been written to the memory card and removed from the buffer. Don’t worry though, they keep coming up with faster and faster processors (although they also keep coming up with bigger and bigger sensors which fill more space!).

NOTE: Camera memory (both internal and memory cads) has gotten to the speed that there isn’t much buffering with smartphones, action cams and drones these days. Even DSLRs can shoot almost continuously in certain modes.

Process All The Things

How Your Camera Works - Hippos
Running Hippo (Hippopotamus amphibius), Ngorongoro Conservation Area, Tanzania.

Information processes before it hits the buffer, making JPEG files, with their smaller size, take up less space in the buffer. Again, different cameras are different. If you are shooting in RAW mode, the information will essentially be written to the memory card untouched while a companion file is saved along with it. This companion file has all the information about the image when it was shot, including what the white balance was, which shooting mode was used, the metering mode at the time, how sweaty your palms were as the crazed hippo was charging your truck….

In JPEG mode, the RAW information compresses to save space. Some cameras have another processor that just compresses files, creating the JPEG files. I discuss RAW vs. JPEG later this month. For now it will suffice to say that RAW files can be 3-5x larger than JPEG and that’s why they take longer to handle.

Lastly, the information writes to a memory card and your image is saved!

I know this information might be basic to some of you and thank you for bearing with me, as I want to make sure the basics are covered.  We’ll begin to pick up speed from here and and get into the meat of Photography Basics.

Experiments For You To Try

Now that you know how your camera works, try these experiments at home:

Tomorrow we will cover Understanding Shutter Speed.

Questions?  Pop ’em like Pez in the comments section below. or email me at

Photography Basics – A 43 Day Adventure, and its companion 40 Photography Experiments, are series written by professional photographer Peter West Carey. The series are designed to unravel the mysteries of photography, helping you can take better pictures. Subscribe here to receive all the updates and bonus material. Your comments are always welcome.

Photo ToursIf you enjoy the series, consider learning photography first-hand on a professionally led international photo tour in Nepal or Bhutan. More information can be found at Far Horizon Photo Tours

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