Photography, explained

The aperture is the adjustable opening in your lens, formed by blades that open and close like an iris. It's written as an f-number: a low f-number (e.g. f/2.8) is a large opening that lets in lots of light, a high f-number (e.g. f/11) a small opening that lets in little. That feels backwards, but the f-number is a fraction: at f/2.8 the opening is the focal length divided by 2.8. Besides the amount of light, the aperture also controls your depth of field — the wider the opening, the blurrier the background.

Shutter speed is how long the sensor collects light, usually in fractions of a second: 1/1000 is a thousandth of a second, 1/30 a thirtieth. The longer the shutter stays open, the more light comes in — but also the more movement you record. A fast shutter speed freezes action, like a bird in flight (often 1/2000 or faster). A slow one makes movement visible instead: flowing water turns silky at half a second or longer, with the camera on a tripod.

ISO determines how sensitive your sensor is to light. A low ISO (e.g. 100) gives the cleanest, sharpest image, but needs plenty of light. A high ISO (e.g. 3200) lets you shoot in the dark without flash or a tripod, but adds grain (noise). It's usually the setting you adjust last, after aperture and shutter speed are already set.

A stop is the unit photographers use to count light: one stop more means twice as much light, one stop less means half. It works for all three exposure settings: going from 1/250 to 1/125 shutter speed, from ISO 100 to 200, or from f/5.6 to f/4 each makes your photo one stop brighter. The f-numbers in the full-stop series (1.4, 2, 2.8, 4, 5.6, 8, 11, 16) are each one stop apart. That lets you trade settings against each other: one stop faster shutter plus one stop higher ISO gives the same brightness. Exposure compensation (+1, −1) is expressed in stops too.

Your camera measures how much light comes from the scene and picks an exposure based on that. Matrix metering (also called evaluative or multi-segment) looks at the whole frame, center-weighted metering mostly at the middle, and spot metering at just a tiny point — handy for a bird against a bright sky. A light meter assumes that whatever it measures is, on average, middle gray. That's why snow comes out too dark (gray) and a black subject too light. You fix that with exposure compensation: +1 to +2 stops for snow, −1 for a dark subject.

A histogram is a graph of every tone in your photo, from black (left) to white (right) — height shows how many pixels have that tone. A spike pressed against the left edge means lost shadow detail (underexposed); a spike against the right edge means blown-out highlights (overexposed). A histogram that mostly sits in the middle, with room on both sides, is usually a safe exposure.

Depth of field is the portion of a photo that's in focus, from foreground to background. A wide aperture (low f-number) makes that zone narrow — great for a blurred background behind a portrait. A narrow aperture (high f-number) makes it wide, so everything from front to back stays sharp — handy for landscapes. Try it with the depth of field calculator.

Handheld, your camera always moves a little, and a long lens shows it sooner. A handy rule of thumb: use a shutter speed of at least 1 divided by (focal length × crop factor). With 300mm on a camera with a 1.5x crop factor that's 1/450, so 1/500 in practice. Image stabilization gives you a few stops of leeway, but only against your own movement — it won't freeze a moving animal. For that you still need a fast shutter speed.

With AF-S (One Shot on Canon) the camera focuses once as soon as you half-press the shutter button, then locks that distance — ideal for still subjects like a landscape or a flower. With AF-C (Servo or AI Servo on Canon) the camera keeps adjusting for as long as you hold the button half-pressed, so a moving subject stays sharp. For birds and other animals AF-C is almost always the better choice, ideally with subject tracking or animal eye detection switched on, if your camera has it.

A lens's focal length (in mm) determines how wide or narrow its angle of view is. A short focal length (e.g. 16mm) captures a wide slice of the scene — a wide angle. A long focal length (e.g. 400mm) pulls a small, distant slice up close — a telephoto. Try it with the calculator's slider.

Not every camera sensor is the same size as a traditional 35mm ("full frame") sensor. A smaller sensor effectively crops a slice out of the image — which makes the same lens appear more zoomed in. Crop factor tells you by how much: a 50mm lens on a sensor with a 1.5x crop factor looks roughly like a 75mm lens on full frame.

A JPEG is already processed in the camera (contrast, color, sharpening) and compressed: small and ready to share, but with 256 tones per color channel. A RAW file keeps all the raw sensor data, usually 4,096 to 16,384 tones per channel (12 or 14 bit). That lets you rescue far more afterwards: choose a completely new white balance, lift shadows or pull back highlights without the image falling apart. The downside: bigger files, and you have to develop them yourself in, say, Lightroom or your camera brand's free software.

Every light source has its own color cast — candlelight is orange, an overcast sky is bluish. Your eyes correct for that automatically; a camera doesn't on its own. White balance (expressed in Kelvin) tells the camera what "white" actually looks like in that situation, so the rest of the colors fall into place. Set too cold, a photo turns orange; set too warm, it turns blue.

The golden hour is roughly the first hour after sunrise and the last hour before sunset. The sun is low, so the light is soft and warm and casts long shadows that bring out shape and texture — exactly what makes landscapes and animals look their best. In the middle of the day the light is harsh and comes from above. The blue hour falls just before sunrise and right after sunset: no direct sun, but a deep blue sky and very even light. Despite the name, it often lasts only about half an hour.

Mentally divide your frame into nine equal boxes with two horizontal and two vertical lines. Place your subject on one of those lines or, better yet, on one of the four intersections instead of dead center — it looks more dynamic and natural. Put the horizon on the top or bottom line, depending on what's more interesting: the sky or the land. Give an animal room in the direction it's looking or moving. Most cameras and phones can show this grid on screen. It's a guideline, not a law: a reflection in water can happily sit symmetrically in the middle.