ISO in Photography: A Comprehensive Guide
- Shawn Eastman
- Jan 24
- 8 min read
Updated: Feb 21
ISO is a fundamental concept in photography, playing a crucial role in determining the brightness of your images. It’s one of the three pillars of the exposure triangle, alongside shutter speed and aperture. Understanding ISO in photography can elevate your skills, enabling you to adapt to various lighting conditions and achieve the desired artistic effect.
This guide will delve into everything you need to know about ISO, including its history, an explanation of ISO settings, practical applications, and tips for mastering it.
Table of Contents
What is ISO?
ISO refers to the sensitivity of your camera’s sensor (or film in analogue cameras) to light.
Originally, the term ISO was derived from the International Organization for Standardization, which standardised the numbering system for light sensitivity. In digital photography, ISO values continue to follow this system, representing how sensitive the camera sensor is to incoming light.
The ISO setting impacts the brightness or darkness of your photos. A low ISO value (e.g., 100) means lower sensitivity and is ideal for bright conditions, while a high ISO value (e.g., 1600 or above) increases sensitivity, making it suitable for low-light scenarios.
However, higher ISO settings may introduce “noise” or grain, affecting image quality - so, in order to allow the sensor to become more sensitive to light and in turn brighten an image, the trade-off is an increase in noise.
ISO Settings Guide
Understanding ISO settings can help you make informed decisions when shooting in various lighting conditions. The table below outlines common ISO ranges, their ideal use cases, and the effects they produce on your images. Use this as a quick reference when adjusting ISO to achieve the best results.
ISO Settings Diagram
ISO and the Exposure Triangle
ISO is one component of the exposure triangle, which also includes aperture and shutter speed.
Together, these settings control the exposure of your photo. While aperture controls the amount of light entering through the lens and shutter speed determines how long the sensor is exposed to light, ISO adjusts the sensor’s sensitivity.
For example:
Low ISO (e.g., 100): Produces cleaner, more detailed images but requires ample light.
High ISO (e.g., 1600): Allows for brighter images in low-light conditions but may introduce noise.
Example of No Noise v Noise
How a portrait photograph could look with a low ISO setting (left) compared with how it could look with a high ISO setting (right).
Note the two example images above - you can clearly see the grainy effect that a high ISO setting has created on the second image.
Modern cameras are capable of using far higher ISO settings than cameras of the past - I remember my first few cameras back in the early 2000's used to introduce noticeable "noise" or grain into an image as soon as I set my ISO at 800 or above (they typically had a max ISO capability of 1600 - although using an ISO this high back then would render images unusable due to the amount of noise that would produce), while modern cameras can easily shoot at ISO settings in the several thousands before noise becomes noticeable.
Some photographers may choose to shoot at high ISO settings to purposefully introduce noise for a creative or nostalgic effect - or because they simply prefer that grainy film aesthetic and have made it a part of their photography style.
How ISO is Measured
ISO is typically measured in values such as 100, 200, 400, 800, 1600, and beyond. Modern digital cameras often allow adjustments in smaller increments (e.g., ISO 125 or ISO 320). The base ISO is the lowest setting available on your camera, usually ISO 100 or 200, offering the highest image quality with minimal noise.
Higher ISO values amplify the signal from the camera sensor, making it more sensitive to light. While this is beneficial in darker environments, it also leads to that often-dreaded increase in digital noise, reducing image clarity.
Vintage family photo with clear signs of noise grain due to the lesser ISO capabilities of older cameras.
Selecting the Right ISO
Choosing the right ISO depends on lighting conditions and your creative intent.
Here are general guidelines:
ISO 100: Best for bright, sunny outdoor scenes. Produces the sharpest and cleanest images.
ISO 400: Ideal for overcast days or indoor shots with good natural light.
ISO 800: Suitable for indoor photography without a flash or in moderate low light.
ISO 1600 or higher: Necessary for night-time photography, indoor events with poor lighting, or fast-moving subjects in dim conditions.
Pro Tip: It's important to recognise that this is only a general guideline because the other camera settings you select (aperture and shutter speed) and the way in which you're shooting (such as using a tripod to shoot using a longer exposure than you'd be able to use shooting handheld) can have a huge say on the ISO you may need to select to correctly expose for an image.
Practical Tips for Mastering ISO
Start with Auto ISO: If you’re new to manual settings, enable Auto ISO to let your camera adjust sensitivity based on the lighting. Review the ISO settings used to learn how they correlate with different situations.
Experiment with Manual ISO: Once you’re comfortable, switch to manual ISO and test various settings. Observe the impact of ISO on brightness and noise. To do this, you can set your aperture, then set your shutter speed, then finally set your ISO to 100 - take a photograph, then increase the ISO in small increments and take another photograph each time - you can them compare them to visually see how the ISO impacts the overall exposure and noise.
For assistance in operating the ISO settings, refer to the camera manufacturer resources - two popular manufacturer resources include Cam.Start.Canon and the Index of Nikon Online Documentation.
Use Low ISO Whenever Possible: In well-lit conditions, opt for the lowest ISO to minimise noise and maximise image quality.
Accept Noise When Necessary: In low light, prioritise capturing the moment over image perfection. A slightly noisy image is better than a blurry one due to insufficient light.
Utilise Noise Reduction Tools: Post-processing software like Adobe Lightroom or Photoshop can help significantly reduce noise in high-ISO images.
Understanding ISO and Noise
As previously mentioned, noise refers to the grainy texture that appears in high-ISO images. While modern cameras handle noise far better than older models, it’s still a factor to consider.
Photographic noise and grain can detract from image quality, but in some cases, it can add an artistic, vintage feel.
To minimise noise:
Use the lowest ISO possible for the lighting conditions.
Opt for noise reduction in post-processing.
Invest in a camera with better low-light performance.
Interesting Academic Study: Characterization of Digital Image Noise Properties Based on RAW Data
Photo taken using high iso setting for creative noise grain effect.
ISO and Different Photography Styles
Wedding Photography: Mastering ISO is crucial for shooting in varied lighting, from sunny outdoor ceremonies to dimly lit receptions.
Night Photography: A high ISO is essential for capturing stars, cityscapes, or other low-light scenes. Combine with wide apertures and slow shutter speeds.
Astrophotography: Requires high ISO settings to capture faint celestial objects, often paired with noise-reduction techniques.
Sports Photography: High ISO combined with fast shutter speeds ensures clear shots of fast-moving subjects in poor lighting.
My Final Thoughts
Mastering ISO is a key step toward becoming a confident and versatile photographer. By understanding how ISO affects light sensitivity, noise, and overall image quality, you can make informed decisions to adapt to any lighting condition. Practice and experimentation will help you find the perfect balance for your unique style.
Elevate your photography by exploring ISO settings, and don’t be afraid to push the limits. Whether you’re shooting a bright landscape or capturing the stars at night, ISO is your tool to unlock the potential of light.
FAQs About ISO in Photography
What is ISO in photography?
ISO in photography refers to a camera setting that controls the sensitivity of the camera's sensor to light. A lower ISO (e.g., 100) makes the sensor less sensitive, requiring more light for a properly exposed image, while a higher ISO (e.g., 3200) increases sensitivity, making it useful in low-light conditions.
How does ISO affect a photo?
ISO affects the brightness and noise in your photos. Increasing ISO brightens an image but can introduce digital noise, reducing image quality. Lower ISO settings produce cleaner images with finer details but may require longer exposure or wider apertures.
What is the "native ISO" of a camera?
Native ISO is the base ISO at which your camera sensor performs optimally, capturing the best image quality with minimal noise. This is typically ISO 100 or 200 for most cameras, but it varies depending on the model.
What ISO setting should I use for outdoor photography?
For bright outdoor conditions, use a low ISO (100-200) for the best image quality. In cloudy, dark or shaded conditions, you might need ISO 400-800+ to maintain proper exposure while avoiding motion blur - unless you can use a tripod and get away with using a longer shutter speed.
Does ISO affect shutter speed and aperture?
Yes, ISO works in conjunction with shutter speed and aperture to determine exposure. For example, increasing ISO allows you to use faster shutter speeds or smaller apertures in low light without underexposing the photo.
What happens if I use too high an ISO?
Using a very high ISO can introduce digital noise or grain, which may reduce sharpness and detail in your photos. Modern cameras handle high ISO better, but it’s still a trade-off between brightness and quality.
Is a lower ISO always better?
Not always - not in terms of being able to best expose an image, anyway. While lower ISO provides better image quality, it may not be practical in low-light scenarios or when shooting fast-moving subjects. Balance ISO with shutter speed and aperture for the best results.
How do I reduce noise at high ISO settings?
To reduce noise, use noise reduction software (like Adobe Lightroom or DxO PureRAW), ensure proper exposure, and shoot in RAW format to preserve details for post-processing.
Can I fix noisy images in post-production?
Yes, noise can be minimised in post-production using tools like Adobe Lightroom, Photoshop, or dedicated noise reduction software. However, excessive noise can still degrade image quality.
Does ISO affect video recording?
Yes, ISO affects the brightness and noise in video recordings. Higher ISO can make videos brighter in low light but may introduce graininess, especially in darker scenes.
What’s the difference between ISO and gain?
ISO is used in photography, while gain is a term often used in videography and refers to amplifying the signal from the sensor. Both affect brightness and noise similarly.
What ISO is best for night photography?
For night photography, ISO between 800 and 3200 is common, depending on your camera's capabilities. Use a tripod to stabilise the camera for longer exposures and reduce noise.
How does ISO affect dynamic range?
Higher ISO settings reduce the dynamic range of an image, meaning you lose detail in the brightest and darkest areas. Lower ISO better preserves the full dynamic range.
What ISO should I use for sports photography?
In sports photography, where fast shutter speeds are essential, try starting with something between ISO 400-1600 depending on lighting conditions. Modern cameras can handle higher ISO with less noise.
Does ISO vary between cameras?
Yes. Some cameras, especially full-frame models, handle higher ISO settings better, producing less noise. Research your camera’s performance to understand its limits.
Why do photos look grainy at night?
Photos at night often require higher ISO to capture enough light, which can introduce digital noise, making the image appear grainy.
What’s the difference between digital and analogue ISO?
Digital ISO boosts brightness electronically, while analogue ISO refers to the physical sensitivity of film or sensor. Modern cameras use a mix of both.
Should I use Auto ISO?
Auto ISO is convenient for dynamic conditions, as the camera adjusts ISO automatically to maintain proper exposure. However, for more control, use manual settings.
How can I practice using ISO effectively?
Experiment with ISO in different lighting conditions. Take the same photo with the same aperture and shutter speed settings and vary only the ISO settings to see how it affects brightness, noise, and overall quality.
What’s the difference between ISO and film speed?
ISO in digital photography is the equivalent of film speed in analogue photography. Both measure sensitivity to light, but ISO is adjustable in digital cameras, while film speed is fixed.
