Film ISO is not the same as digital ISO. In film, ISO is a chemical property of the film itself. Every roll of film has a particular ISO rating which determines how sensitive it is to light. . In digital cameras, ISO determines the amount of light absorbed by the sensor to build an image.

In this article, I have covered basic topics such as ISO in film, ISO in a digital camera, why is ISO important, how it affects the photo quality, and an overview of the exposure triangle.

What is ISO in film?

ISO in a film camera is not set at a push of a button. Instead, each film has a separate ISO rating which relates to the light-sensitive emulsion layer on the film. This rating can also be called film speed.

What is ISO in a digital camera?

In digital cameras, ISO speed is a number that indicates light sensitivity of the CCD or CMOS sensor. CCD or CMOS is a sensor technology, or the digital equivalent of film.

Why do digital cameras have ISO anyway?

The ISO setting in a digital camera is what makes it versatile. The lowest setting of ISO on a digital camera is usually 50, 100 or 200, while the highest setting is around 3200 or 6400, or even greater in some camera models.

When the ISO setting is low, the sensor is least sensitive to light. The sensor is more sensitive to light when the ISO setting is high. The ISO settings in a digital camera can be changed after every click if necessary. It gives an advantage to the digital cameras to be able to click correct exposed pictures even in low light.

When your ISO is at a higher level, you risk getting a lot of noise in your photo, but through digital cameras, you can keep the ISO a little lower and adjust the shutter speed and aperture to avoid the grain or noise. The manual settings on your digital camera allow you to choose the correct ISO as per your requirements.

How does ISO affect photo quality?

ISO will either brighten your photo or darken it. If your ISO number is high, the picture will be brighter and if your ISO number is low, your photos will be darker. Choosing the correct ISO can help you capture images in darker environments and lets you better adjust the aperture and shutter speed. However, selecting a high ISO could show a lot of grain in your photo, also known as noise.

Hence, you should increase your ISO only when you cannot brighten the picture with shutter speed, exposure, and aperture.

If you use a low ISO setting such as 300, your photo would be of a higher quality. For example, shooting outdoors under direct sunlight benefits from low ISO settings. Landscape photographers usually choose a lower ISO setting to make sure that the photos do not look over-exposed or grainy.

ISO comparison between 100 and 6400

The exposure triangle: ISO, shutter speed and aperture

Photography consists of 3 main elements – ISO, Shutter Speed and Aperture. Aperture is the depth of the field and the amount of light let on to the sensor or film, shutter speed is related to motion, and ISO is related to light sensitivity.

Whichever type of photography you do, these three elements are at the centre of every correct exposed photograph. There are many combinations of aperture, shutter speed and ISO that can be used to get the correct exposure. The combination you choose will reflect your artistic vision for a picture.


Aperture or F/stop controls how much light will go into your camera lens, which in turn will determine what your exposure will look like. It determines how wide your camera lens will open.

Shutter Speed

Shutter speed determines how long will the lens stay open to let a specific amount of light into the sensor. It is measured in fractions of seconds to multiple seconds for longer exposures.

A faster shutter speed will have the effect of freezing motion and a slower shutter speed will have the effect of blurring motion in a picture.


ISO determines how sensitive a photographic film emulsion or digital sensor is to light. An increase in ISO allows you to work even in low light and a lower ISO would be appropriate for brighter surroundings.

If you double the ISO it will result in a one-stop increase in exposure and halving the ISO means reducing the exposure by one stop.


In conclusion, ISO is an important setting in the exposure triangle and it vastly affects the photo quality.

Setting the ISO to a lower setting will give you better quality pictures than higher ISO settings. ISO in film and ISO in digital cameras differ, but both have the same outcome – a perfectly exposed image.