How a camera makes a picture
The simplest camera is a pinhole camera: a dark box with a tiny hole. Light from each point of an object travels in straight lines through the hole and makes an upside-down image on the back wall.
A real camera swaps the pinhole for a lens, which gathers more light and focuses it sharply. Behind it sits a sensor (digital) or film (analogue). The shutter opens to let light in.
Analogue photography uses light-sensitive film developed with chemicals in a darkroom. Experimental methods include cyanotypes (sun prints on treated paper) and photograms (objects laid on photo paper). Digital cameras turn light into numbers (pixels) that can be stored, edited and shared.
Exposure: aperture, shutter speed and ISO
Exposure is the total light that makes the photo. Too much = overexposed (washed out). Too little = underexposed (dark).
Aperture (f-number)
f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16. Each step lets in half the light of the one before. A small f-number is a big opening. Aperture also controls depth of field: f/2 gives a blurred background (good for portraits); f/16 keeps near and far sharp (good for landscapes).
Shutter speed
1/1000 s, 1/500 s … 1/15 s. Each step doubles the time and the light. Fast speeds freeze motion; slow speeds show motion blur (silky waterfalls, light trails). Below about 1/60 s use a tripod.
ISO
ISO 100, 200, 400 … Doubling ISO doubles brightness but adds noise (grain).
One "stop" = double or half the light. Open the aperture one stop and use a shutter one stop faster: the exposure stays the same. This trade-off is the exposure triangle.
Focus and light
Focus: choose what must be sharp, usually the eyes in a portrait. Autofocus picks a point; manual focus lets you decide.
Light makes the mood:
- Direction: front light is flat; side light shows texture and shape; back light makes silhouettes and glowing edges.
- Quality: hard light (midday sun, bare bulb) gives sharp shadows; soft light (cloudy sky, window with a curtain) gives gentle shadows.
- Colour: the golden hour after sunrise and before sunset is warm; shade is bluish. White balance corrects this.
- Studio basics: key light (main), fill light (softens shadows), back light (separates subject); a reflector can be a white card.
Composition and framing
- Rule of thirds: place the subject on the lines or crossings of a 3 × 3 grid.
- Leading lines: roads, rails or rivers guide the eye into the picture.
- Framing: use a doorway, window or branches around the subject.
- Viewpoint: shoot from low (makes things look powerful) or high (makes them look small).
- Shot sizes: wide (place), medium (person and action), close-up (detail, emotion).
- Balance, symmetry, pattern, negative space and fill the frame are other tools.
Rules are guides: break them on purpose when it makes the picture stronger.
Telling stories, editing and photomontage
A photo story (still-image narrative) uses a sequence of pictures: an establishing wide shot, people and action, details, and a closing image. Captions add facts.
Editing: crop, straighten, adjust exposure, contrast and colour. Photomontage combines several photos into one new image, by hand (cut and paste) or digitally (layers).
Ethics: ask people before photographing them, respect privacy, never present a heavily changed photo as real news, and credit other people's images.
Photography is part of daily life: news, science, advertising, family memories and social media.
Reading and critiquing a photograph
Use four steps:
- Describe: what do you see? Subject, setting, colours.
- Analyse: how is it made? Light, composition, focus, shutter, viewpoint.
- Interpret: what does it mean or make you feel?
- Judge: does it work? What would you change?
Study the work of many photographers, from early portrait and documentary photographers to today's artists, and note how each uses light and framing.
Try it: a pinhole and a thirds grid
Make a pinhole viewer: a shoebox with a pin-hole on one end and tracing paper on the other. Point it at a bright window in a dark room and see the upside-down image. Then turn on the grid in your phone camera settings, and take one photo with the subject in the centre and one on a thirds crossing. Which looks more alive?
Key formulas and definitions
- Exposure = aperture (how much) + shutter (how long) + ISO (how sensitive)
- f-stops: f/2 → f/2.8 → f/4 → f/5.6 → f/8 → f/11 → f/16 (each halves the light)
- Light through aperture ∝ 1 / (f-number)²
- 1 stop = ×2 or ÷2 light
- Shutter: 1/125 s → 1/60 s doubles the light
- Rule of thirds: subject on a line or crossing of a 3 × 3 grid
Worked examples
1. You change from f/4 to f/8. How much light now?
f/4 → f/5.6 → f/8 is 2 stops. Each halves the light: ½ × ½ = ¼ as much.
2. A photo at 1/125 s is too dark by one stop. Which shutter speed fixes it (same f and ISO)?
Double the time: 1/60 s.
3. You want to freeze a cricketer's bat swing. Which setting matters most?
A fast shutter speed such as 1/1000 s.
4. You want a portrait with a soft, blurred background. Which aperture?
A wide aperture (small f-number) like f/2 for shallow depth of field.
5. Correct exposure is f/5.6, 1/125 s, ISO 100. You change to f/11 and ISO 400. What shutter speed keeps the same exposure?
f/5.6 → f/11 = 2 stops less light. ISO 100 → 400 = 2 stops more. They cancel, so keep 1/125 s.
6. At night you raise ISO from 400 to 3200. How many times brighter? What is the cost?
400 → 800 → 1600 → 3200 = 3 stops = 2³ = 8 times. The cost is more noise (grain).
Common mistakes
- Thinking f/16 is a bigger hole than f/2. A bigger f-number means a smaller opening.
- Using a slow shutter without support, causing camera shake.
- Always putting the subject in the dead centre.
- Raising ISO first in low light when a wider aperture or tripod would keep the image cleaner.