Photography Tutorial: Mastering The “Exposure Triangle”

Aperture, shutter speed, and ISO. Ready, set, go!

Example of a wide aperture/small f-stop number (f1.8), where the subject is isolated. PHOTO Tracy Cheng

The three most important variables in photography are what is commonly known as the “exposure triangle”: aperture, shutter speed, and ISO.

An easy way to describe what an ‘aperture’ is is to think of like the pupil in your eye.  The aperture is the measure of how big or small the ‘hole’ in the camera lens is.   Just like the pupil filtering light that enters your eyes, the hole allows the photographer to control the amount of light to be filtered through to the lens. The wider the aperture, the more light the lens will allow in.

The aperture is measured by the “f-number” in a camera, where the smaller the f-number, the wider the aperture is.  A small f-stop number gives a narrow depth of field, which allows focus on one particular subject (e.g. in a portrait photo where only the subject’s face will be in focus but the background is blurred).  Higher f-stop numbers give smaller apertures, which allows for a greater depth of field.  This means that more of a scene can be in focus (e.g. in a landscape photo, everything will be in focus).

Example of a small aperture/high f-stop number (f5.6), where everything is in focus. PHOTO Tracy Cheng

Shutter speed

The shutter speed measures how long the shutter remains open; the longer the shutter remains open, the more light is let into the lens.  Shutter speeds are measured in seconds, where a typical DSLR will usually allow for cameras to have their shutters open for up to 30 seconds.  Having a shutter open for that long allows for the camera to capture night scenes clearly.  Note that the camera will capture everything while the shutter speed remains open, which means that any shake or movement is also captured.  This is why photographers require tripods, so that the cameras will remain stable while the shutter speed is open for that long.

Example of a long exposure shot with a shutter speed of 30 seconds on a tripod. PHOTO Tracy Cheng

A fast shutter speed allows minimal light into the lens, but allows for motions to be captured.  A fast shutter speed can be anywhere from 1/250th of a second to 1/6th of a second.  The faster the shutter speed (with the right amount of light let in), the sharper the image.

Example of a fast shutter speed 1/100 seconds, capturing water splashes. PHOTO Tracy Cheng


ISO measures how sensitive a camera is to light.  The lower the ISO, the less sensitive the camera is to light and vice versa.  Higher ISOs allows photos to be shot without a flash in low-light settings, but also create ‘grainy’ camera effects, so it is always best to shoot photos in the lowest ISO possible (and compensate by shutter speeds and aperture settings).

Example of a grainy image, shot at a high ISO (ISO 1600), handheld (no need for a tripod). PHOTO Tracy Cheng


Example of a non-grainy shot at a low ISO (ISO 200), on tripod. PHOTO Tracy Cheng

Check out Tracy’s website for more tutorials. 

Tracy Cheng

Contributor, JST SHOP Vendor

Tracy loves photography and documenting her travels. She has lived in Hong Kong, London, Toronto and Los Angeles, and has a piece of her heart in each city.

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