After writing on several aspects of exposure the past few weeks,  we will end this beginners-course with a post on ISO. As mentioned before ISO is not a part of exposure because it influences the brightness of your photo AFTER the light is recorded by the camera sensor as opposed to exposure settings which influence the amount of light that reaches your camera-sensor. However, it is good to know about ISO, because it gives you a bit more freedom to adjust other settings (like aperture and shutter-speed) to your liking given a certain amount of time.

What does ISO mean?

In analog photography ISO (/ ASA) was the mark of how sensitive a film was to light. This light sensitivity was indicated by a number; the lower the number the lower the sensitivity of the film. The main governing body that, amongst other things, standardizes sensitivity ratings for camera sensors is the International Organization for Standardization. Many photographers think ISO is an acronym of this organisations name.However, because  the name would have different acronyms in different languages (IOS in English, OIN in French for Organisation internationale de normalisation), they decided to simply name the sensitivity ISO. And ISO is derived from the Greek isos, meaning equal.

Is ISO about sensor-sensitivity to light?

Well, actually: no. As stated before ISO stated the sensitivity of film to light in analog photography. At higher ISO-numbers, the resulting photos will be darker at a given exposure-value (EV). Conversely, at lower ISO-numbers, the resulting photos will brighter at a given EV.

In digital photography the brightness of your photos will still change when changing the ISO-setting on your camera. However, strictly speaking the light sensitivity of a camera does not change when adjusting ISO-settings. ISO is simply a post-sensor gain applied to the signal from the camera sensor.

What do the ISO-numbers mean?

Digital cameras (DSLRs) typically have ISO-settings that range between 100 (low sensitivity) to 204,800 or even higher (high sensitivity). Compact cameras and camera phones will have lower maximum ISO-settings than DSLRs.

Effects of changing ISO

Changing ISO-setting influences the brightness of your images and it changes the signal to noise ratio. It also has (some) effect on color and dynamic range (the ability of the camera to capture detail in both highlights and shadows)

Effects of changing ISO: brightness

The effects are:

  • The lower the ISO-setting, the less gain applied to the signal from the camera-sensor and the darker the resulting photo will be at a given EV.
  • The higher the ISO-setting, the more gain applied to the signal from the camera-sensor and the brighter the resulting photo will be at a given EV.

The gain applied to the signal will double between each ISO-setting. This means that doubling the ISO-setting will double the brightness of your photo and increase the EV by one stop. Conversely, halving ISO-setting will halve the gain applied to the signal, decreasing the EV by one stop.

These stops are, again, the same as the ones when adjusting aperture or shutter-speed. This means that when you increase or decrease the shutter-speed and or aperture by a number of stops, you can adjust the ISO in the opposite direction by the same amount of stops. The brightness of your image should remain the same, however motion-blur might, depth-of-field (DOF) will and the amount of noise might change between settings. Remember the exposure triangle! Figure 1 gives you examples of how the brightness changes resulting from changing the ISO-settings.

example iso brightness lego photography ultimate guide

Lastly, brightness can also be changed in post-processing. Yet, the quality of the photo will usually be better if the ISO is set correctly in the camera as opposed that adjusting the brightness in post-processing.

Effects of changing ISO: signal to noise ratio

Image quality will change when adjusting ISO. The higher the ISO is set, the higher the amount of noise (/ grain) in your photo will be. The lower the ISO, the lower the amount of noise in your photo.

The signal to noise ratio depends on the sensor in your camera. In general the smaller the sensor; the more noise a sensor will produce.

Besides, as said before ISO is about the amount of gain applied to the signal that is produced by the sensor after exposure to light. And the higher the ISO, the higher the gain applied to the signal. However, the gain is applied to both the noise and the signal. So, at higher ISO-values the noise becomes visible. Figure 2 shows you the noise in pictures at differing ISO-settings. The EV is equal because I adjusted shutter speeds.

example iso noise levels lego photography

Okay, to be honest, I never tested my camera (like I recommend later on in this post) until I decided to create figure 2 today. As it turns out, my camera is pretty good with noise levels, I need to go to very high ISO-levels to get an amount of noise that is not acceptable anymore. In the end, figure 2 loses some value because of this. Just compare the level of noise at ISO 100 with the level of noise at ISO to get an idea of what is possible. Also recognise the difference in color and dynamic range between the two most extreme settings.

Setting your ISO

Most cameras only have aperture- or shutter-speed priority mode. In these modes you usually can set a range of ISO-values from which the camera can choose. As far as I know only Pentax camera’s have an ISO-priority mode. And of course you can use Manual (M-)mode.

Test the ISO noise-effects of your camera

Each camera sensor differs with respect to ISO. It is best practice to test your camera at differing ISO settings, deciding for yourself which amount of noise is acceptable. Be sure you judge the amount of noise on your computer (!) and not on a small telephone of camera-screen. Also remember that noise is usually higher in darker photos at a given ISO-setting.

Choosing your ISO-settings

All in all it is recommended to shoot your photos at the lowest ISO-number possible. This will produce the best quality photos. Also keep in mind that quality of color and dynamic range increases at lower ISO-settings.

However, sometimes that may not be possible. The worst circumstances being if you want a relative small aperture whilst freezing motion (high shutter-speed) in a photo at low light shot from the hand. That photo will not be possible without increasing ISO-values.

Anyway, I almost exclusively use ISO 100 when shooting Lego. The fact that Lego scenes are usually pretty static makes it so that I can usually shoot from a tri-pod at low shutter-speeds without needing to increase ISO. Yet, sometimes I still need to increase ISO, this is almost exclusively due to the need of a certain shutter-speed. For example, to freeze the motion of an object in the scene but mostly because I need a higher shutter-speed because I can’t use my tripod and need to take a picture from the hand. A higher ISO means I can use faster shutter-speeds with a lower chance of camera-motion due to my hands shaking.

Conclusion

This post concludes the course on the basics of camera-settings. Reading about exposure, aperture, shutter-speed and ISO, understanding how these values relate to each other and practice will surely increase the quality of your (Lego) photography. Besides, it will give more freedom to photograph a scene exactly as you like.

If there are any more questions, let me know in the comments!


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