ISO in Photography: Simple Rules of ISO Settings

Varvara January 01 2022

You have probably already discovered the ISO setting on your camera, but you never really knew what it was for. In addition to aperture and shutter speed, the ISO value also has a great influence on the exposure of the image. It controls the light sensitivity of the sensor in the camera. Let’s learn more about ISO settings on your camera and how to use ISO to enhance your photography.

ISO meaning on the camera

To illustrate ISO, let's imagine the camera's sensor as our eyes. Everyone knows that when you turn off the light in the evening, it takes a while for your eyes to get used to the darkness. 

If you turn the light on again, a sometimes harmless table lamp appears extremely bright for a short time and you have to squint your eyes until you get used to it again. The reason for this is that our optic nerves adjust their sensitivity to light according to the brightness. 

And that's exactly how it behaves with the camera's sensor, except that we can adjust its sensitivity there as we wish via the ISO setting.

ISO meanings for different light conditions

The sensitivity of the ISO sensor is expressed and set in concrete numbers. ISO values ​​of 200, 100, or less indicate a low sensitivity to light. Such values ​​are ideal for taking photos in situations with sufficient light, for example on a cloudless, sunny day outdoors. 

But imagine that large, dark clouds are pulling in front of the sun. In order to be able to expose the picture correctly with ISO 100, you would either have to open the aperture further or set the exposure time so long that you need a tripod to get blur-free pictures. 

If neither is an option, you can increase the ISO value to counteract this. This is because it provides more leeway for setting different time/aperture combinations. The higher you set the ISO value, the more sensitive the sensor reacts to incident light. 

Values ​​from 400 to 800 are usually used for cloudy days or indoors where there is not much light. 

Values ​​from 1600 can be used in poor lighting conditions, where no flash can or may not be used (e.g. in event photography at concerts, in theaters, etc.)

Photography with only on-site light has even been given its own area in photography - available light photography - here you often need cameras that still produce usable images even at high ISO values.

ISO values ​​and image noise

The rule of thumb is simple. Is the shutter speed too slow? ISO value goes up. Taking photos with the aperture closed in dim light? ISO value should be even higher. 

Unfortunately, as is so often the case, there is a catch. Depending on the respective camera model, the image quality deteriorates considerably with increasing ISO value. So-called image noise and the loss of details in the recording can occur. Many compact cameras and older bridge cameras have a clearly visible noise from ISO 800.

If you want to take photos without flash in poor light conditions, you should use a reflex camera (DSLR) or a mirrorless system camera (DSLM). Their significantly larger sensors (mostly MFT or APS-C) can still take reasonably usable images even at higher values, with ISO 1600 and more). 

The larger the sensor of the camera, the better the noise behavior is usually. If you have the highest demands on image quality in low light, you have to use cameras with full-format sensors. These are significantly larger, i.e. MFT or APS-C sensors. However, depending on the manufacturer and model, these cameras can be very expensive.  

The most important rule of ISO

But even with these and even better models, the rule applies: less is more! It is always advisable to start taking photos with low ISO values and only increase the value when the required combination of time and aperture is no longer feasible with the best will in the world. Therefore, be careful with the ISO value. Your photos will thank you.

Use of the ISO value - what to do when it gets dark?

It is not always possible to avoid using a high ISO value. An example: You take photos with the aperture open at ISO 800 without a tripod and without a flash at a party. You, therefore, need the shortest possible shutter speed, which should not be less than about 1/40. 

If the shutter speed has to be set so long that your pictures blur, the slightest picture noise will not do you any good. Now you can raise the ISO value to 1600 or even 3200 and, in contrast, reduce the shutter speed again. Noisy pictures are better than totally blurred! 

Of course, depending on the lighting situation, you have to try to find the best compromise. And sometimes even the best camera won't do you any good. Because where there is no light, there can be no picture. 

Do you remember the comparison between ISO and the eye optic nerve? Where there is no light, we cannot see anything. In that case, you have no choice but to put your camera away or use a flash.

Using ISO for RAW format

Some bridge cameras and almost all SLR cameras offer you the option of reading out your photos in raw data format, the so-called RAW format. In other words, these RAW data are the “digital negatives” of your images. 

Unlike the JPEGs created by your camera, RAW files remain completely unprocessed. When you convert your images into JPEGs, the software in the camera processes the images - brightness, contrast, and saturation are added and image noise is removed with various filters. 

Unfortunately, the latter often work very hard and image information is irrevocably destroyed. Not so with the RAW format. 

On the one hand, you have the option of later editing images on the computer with special noise filter software to remove significantly more image noise and, on the other hand, to preserve more details and sharpness in the photos. The RAW format offers other advantages but is labor-intensive and very memory-hungry (up to 40MB per image).