Module 1 · Know Your Camera
How a camera works
Lesson 1 of 12
MODULE 1 ROADMAP
The short version
Every camera, from a phone to a big studio camera, does the same simple job: it lets light in through a lens, for a moment you control, onto a sensor that records it. Once you can picture that path, every button on your camera starts to make sense.
New to this?
Think of a camera as a dark box with a window at the front. The lens is the window, the sensor at the back is the "film", and you decide how wide the window opens and for how long. That is genuinely the whole idea. Everything else is detail, and you will learn it one friendly piece at a time.
Follow the light
Picture pouring water into a bucket through a funnel. How much ends up in the bucket depends on how wide the funnel is and how long you pour. A camera works the same way with light.
The lens (the glass at the front) bends the light so the scene lands sharply on the sensor. Inside the lens is the aperture, an opening that can be made wider or narrower: that is your funnel width. The shutter opens and closes to decide how long the light pours in. The sensor, a chip covered in millions of tiny light-catchers, records the light. Finally the processor (the camera’s small computer) turns that recording into a picture file and saves it to the memory card, or to built-in storage on a phone.
Can you spot the odd thing in Figure 1? The picture lands on the sensor upside down. Every camera does this, and the processor quietly flips it back for you. There is one more control you will meet soon: ISO, which sets how much the sensor’s signal is boosted, a bit like turning up the volume (Module 5).
The main kinds of camera
- Phones have small sensors and clever processors that blend several frames into one picture.
- Compacts and bridge cameras have a lens that is built in and never comes off.
- DSLRs and mirrorless cameras take lenses that you can swap.
- Medium- and large-format cameras use even bigger sensors or sheets of film, mostly for landscapes, studios and fine detail.
Lesson 3 lines them all up side by side.
DSLR or mirrorless: the one real difference
A DSLR (digital single-lens reflex) has a mirror in front of the sensor. The mirror bounces the light up to the viewfinder, so you see the real scene through the lens. When you press the button, the mirror flips up for a moment and the light reaches the sensor.
A mirrorless camera has no mirror. Light goes straight to the sensor all the time, and the viewfinder or screen shows you the sensor’s live picture, so you can see how bright the photo will be before you take it.
Bigger and smaller sensors
Sensors come in different sizes. The usual yardstick is full frame, the size of a frame of classic 35mm film. APS-C and Micro Four Thirds are smaller, many compacts use a 1-inch type sensor, and most phone sensors are smaller again. Medium format is bigger than full frame.
A smaller sensor records a smaller middle part of the picture the lens makes, so the same lens looks more "zoomed in". Bigger sensors catch more light overall, which usually means cleaner pictures in dim light; smaller ones mean lighter, cheaper kit. Neither is better. Lesson 4 shows you exactly how it works with a real photo.
Go deeper
Equivalence. For the same framing and print size, depth of field and total light gathered both scale with the f-number multiplied by the crop factor. A 25mm f/1.4 lens on Micro Four Thirds (crop factor 2) frames like 50mm on full frame and gives roughly the depth of field of 50mm at f/2.8. Exposure is different: f/1.4 is f/1.4 on any sensor, so the meter reading is identical. The smaller sensor collects about two stops less total light, which is why its noise at a given ISO looks roughly like full frame two stops higher.
Why the image is upside down. Rays from the top of the scene cross through the lens and land at the bottom of the sensor, and left swaps with right. Optical viewfinders use a mirror and prism to turn the view upright again; electronic displays simply redraw it.
Finn tip: Keep a PDF of your camera’s manual on your phone. When a button puzzles you in the field, search the PDF instead of guessing. Every photographer does this, including the pros.
Easy traps (we have all fallen in)
- Thinking the camera body makes the picture. The light, the lens and your choices matter far more.
- Believing a smaller sensor changes a lens. It changes how much of the picture gets recorded, not the lens.
- Judging brightness through a DSLR’s optical viewfinder. It shows the scene, not the photo, so check the screen afterwards.
Key takeaways
- Lens focuses, aperture sets how much light, shutter sets how long, sensor records, processor saves.
- DSLRs show you the real scene; mirrorless cameras and phones show you the sensor’s live picture.
- Smaller sensors record a smaller part of the lens’s picture, so the same lens looks more zoomed in.
Try it now · 10 minutes
Find your camera’s sensor size: search your camera’s model name plus “sensor size”. Write it on a sticky note and put it in your camera bag. You now know something about your camera that plenty of owners never look up. Nice work.