As a photographer, you must have heard about ISO. ISO, Aperture, and Shutter Speed are considered the three pillars of photography. Sometimes they’re referred to as the holy trinity of photographic exposure. Together they determine how much light is captured by the sensor.
ISO denotes the sensitivity of the sensor to light. It’s expressed as a number that reads like ISO 100, 200, 400, 800, and so on. Every number is double the previous number and is referred to as one stop. Sometimes it’s also referred to in a third of a stop, such as 100, 125, 160, 200, and so on. Every incremental number pushes the sensor’s sensitivity, allowing it to amplify the light signal and capture a decently exposed photograph.
What is the purpose of ISO?
The purpose of ISO is to ensure that you can capture a good exposure in a low light situation without having to slow down the Shutter speed or use a large aperture. ISO allows you to work even in low light and create an image that appears shot in good light.
There are three ways to control exposure. You can use a large Aperture (lens opening) to let a lot of light into the camera. Alternatively, you could use a slow Shutter Speed, increasing the time for the shutter curtain to remain open and collect light. The third option is to shoot with a high ISO number.
When is a higher ISO necessary?
A higher ISO is necessary when you cannot control the other two parameters, Aperture and Shutter speed. Let’s take a few examples. Let’s assume you’re shooting with a kit lens that opens up to an Aperture of f/5.6 at its tele-end, but you need a slightly wider Aperture to ensure proper exposure. In such a situation, you could try and compensate by slowing down the Shutter speed. But what if shooting with a slower Shutter speed isn’t feasible? For example, is the recommended Shutter Speed slower than what you could hand holding the camera? The solution, in this case, is to push the ISO.
When isn’t a higher ISO necessary?
A higher ISO isn’t necessary for the following conditions –
- When you can use a tripod to stabilize the camera and shoot with a slow Shutter Speed.
- When you’re using a combination of a fast wide aperture and a slow shutter speed that you can hand-hold.
- When you’re shooting in sufficient ambient light.
- When you’re good, you can control studio lights as per your needs.
Problems of using a higher ISO
Higher ISO leads to noise. This happens because, at higher ISO, the lack of light produces noise, and the higher the ISO, the more that noise gets amplified. This phenomenon is visual and can be seen as graininess in your images. You will see the nose’s impact more in the image’s shadow areas than in the brighter areas.
It’s pertinent to know here that ISO does not add to the amount of light captured by a sensor. It’s merely amplifying the light signal. Therefore, where the light signals are poor, such as when there is a lack of light in a scene, any amplification of the light signal will also amplify the noise.
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