The Exposure Triangle: Aperture, Shutter Speed, ISO Explained

The exposure triangle refers to the balance between three camera settings that affect the brightness of an image. When shooting photos with your Galaxy’s Pro mode, you only have to worry about striking a balance between two of them (since your phone’s aperture is set in stone).

What are the three parts of the exposure triangle?

On the exposure triangle, each of the triangle’s three vertices, ISO, aperture and shutter speed, affects the image differently, with different side effects:

• Aperture refers to the size of the hole that light passes through on its way to the sensor. The bigger the hole, the more light comes through and the blurrier the background is.
• Shutter speed refers to the amount of time the sensor is exposed to light, and controls motion blur (longer exposures result in motion blur, while short exposures freeze action).
• ISO refers to the level at which the sensor’s output is amplified; the higher the ISO, the brighter the image but the noisier it gets.

All three are measured in stops; increasing or decreasing a value by one stop doubles or halves the amount of light, respectively. This means that one can compensate for changes in exposure by modifying more than one variable (for example, increasing the ISO by one stop and decreasing the exposure time by one stop would result in no net change in exposure).

Unfortunately, on the Galaxy you can only control two of the three; aperture is determined by the lens, so Pro mode only allows you to control shutter speed and ISO (although there is an exposure compensation option as well).

Can you change the aperture on a Samsung Galaxy?

No. On current Galaxy phones the aperture is fixed for each lens, so there's no aperture setting in Pro mode.

The size of the lens opening is referred to as the aperture and is expressed as an f-number. A lower f-number (such as f/1.4) represents a wider lens opening; a higher f-number (such as f/16) represents a narrower opening. A wider aperture gathers more light and produces images with less of the frame in focus; a narrower aperture gathers less light and produces images with more of the frame in focus. Aperture is one of the key tools for creative control when shooting on a dedicated camera.

On current Galaxy phones, the aperture size is fixed for each lens, so you won’t find an aperture option in Pro mode. On the S25 Ultra, the aperture sizes are f/1.7 (wide), f/2.4 (3x) and f/3.4 (5x). On the S26 Ultra, they’re f/1.4 (wide), f/2.4 (3x) and f/2.9 (5x). The S26 Ultra’s main camera can therefore capture images with more light. And with Portrait mode, most of the background blur effect will be added digitally.

Shutter speed and the handheld limit

How long does the Galaxy phone’s camera sensor gather light for when taking a picture? That’s controlled by the shutter speed. Fast shutter speeds (think 1/1000s or 1/2000s) can freeze fast-moving action; slower shutter speeds (1/30s, 1 second, 30 seconds) will blur motion or create light trails. As a rough guide for shooting handheld, use a shutter speed faster than the reciprocal of the focal length (expressed in 35mm-equivalent terms). So, say, for the main camera on a Galaxy phone (35mm-equivalent focal length of about 24mm), use a shutter speed faster than about 1/30s to minimise the chances of camera shake being noticeable; for a 5x telephoto camera (35mm-equivalent focal length of about 111mm), use a shutter speed faster than about 1/120s. (Optical stabilisation lets you go a little slower.) This rule of thumb doesn’t apply if your subject’s moving (use a fast shutter speed to freeze their motion) or you’re using a tripod (in which case you can take advantage of the Galaxy phone’s maximum exposure time in Pro mode – 30 seconds on flagships). At either extreme, the shutter speed guide gives an example.

ISO and noise

ISO is the level at which the camera’s sensor amplifies its signal. Higher ISOs result in brighter images at the same shutter speed, but with more noise (graininess) in the image. Noise on the Galaxy starts to become visible at higher ISO settings (about ISO 3200 and up), and at lower ISO settings (up to about ISO 800) the Galaxy’s noise reduction does a decent job of removing noise without overly smoothing images (removing detail such as in trees or hair, which can sometimes look worse than noise). If your Galaxy offers ISO 50, this will result in the cleanest images.

Choose your ISO setting last and keep it as low as possible given your desired shutter speed (or lower it and lengthen your shutter speed if shooting on a tripod). It’s better to have a noisy image than a blurry one, so don’t be afraid to crank up the ISO when shooting handheld in low light to maintain a fast enough shutter speed. Shooting in RAW can give you additional noise reduction options when processing your images.

How do aperture, shutter speed and ISO trade off?

Stops refer to doubling/halving the amount of light reaching the sensor. So, if you want to keep the same exposure, but change the exposure time from 1/125s to 1/60s (twice as much light), you need to either close the aperture by one stop (e.g. from f/2.8 to f/4) or change the ISO from e.g. 400 to 200.

It works the same the other way around: if you increase the ISO from 200 to 400 (+1 stop), you either have to reduce the exposure time from 1/60s to 1/125s or close the aperture by one stop (e.g. from f/2.0 to f/2.8).

On a Galaxy you don’t have a choice of aperture, so it’s all shutter speed vs. ISO. Exposure compensation just tells the camera that you want an exposure brighter/darker than what the camera’s light meter thinks is correct.

Galaxy Pro mode starting points

The following starting points show you how the triangle works on a Galaxy phone. The aperture is whatever your camera lens will allow, so each row is a compromise between shutter speed and ISO. The Pro mode guide adds white balance and focus for each scene.

Should I set shutter speed or ISO first on a Galaxy?

Start with shutter speed and ask yourself what you want frozen or smeared by motion. Then set ISO as low as you can get away with for a bright enough image. Aperture would come next, except on a Galaxy it’s already been chosen for you by the lens.

A similar process happens in Photo mode on Auto, with the camera choosing a fast enough shutter speed to avoid camera shake and compensating with ISO as needed to maintain a certain level of brightness. In fact, in One UI 8.5, Samsung’s Camera Assistant can tell the camera to use a minimum shutter speed and maximum ISO in Photo mode, so you get to see two corners of the triangle at work.

The difference with Pro mode is that you’re making the compromise. Maybe you don’t mind a long exposure because you’ve got the phone on a tripod and you’d prefer to keep ISO low, or maybe you need a fast shutter speed to photograph some action in poor light and can put up with a noisier image.

Exposure compensation, the fourth control

You may also see EV for exposure compensation (it's not part of the triangle). It lets you tell the camera to take brighter (+EV) or darker (-EV) pictures than it thinks they should be. In the latest versions of One UI you can also change exposure compensation in Photo mode. After tapping to focus, drag the slider up or down next to the focus circle. Pro mode also has an exposure compensation setting. EV stands for exposure value, and changing the EV by 1.0 changes the exposure by one stop (i.e. +1.0EV will make the picture twice as bright, -1.0EV half as bright). Raise EV for backlit subjects. Use exposure compensation of around +0.7EV when shooting snow (otherwise it often comes out grey rather than white) and around -1.0EV when you want to silhouette something against a bright sky. Exposure compensation only works when the camera still has some control over exposure. For example, according to Samsung's guide to Pro mode, if you change the shutter speed, ISO sensitivity can't be set to Auto (according to an older Samsung guide, exposure compensation can't be changed either). At that point you'd control exposure using ISO sensitivity and shutter speed.

Balancing act! In week 2 of the 30-day photography challenge (our free course) we’ll look at Pro mode for shutter speed and ISO, one setting at a time! The 90-day challenge builds manual control into a longer plan.