The ISO

The ISO is one of the three components of the Exposure Triangle. The ISO rating is used to measure the media sensitivity to the light whether you use film or a sensor (in a Digital camera).

Ability to change your ISO is a blessing

If there is one major feature that came from the Digital camera revolution, it has to be the ISO setting that enables you to change the sensor sensitivity at will, after every single shot. As a matter of a fact, before the 1990s all cameras used a roll of film of an unchangeable ISO rating (i.e. a 100 ISO roll). Should one needed to use 400 ISO for a particular situation, he/she would have needed to remove the roll of film located int eh camera and in that process any part of the film that was unused at that time (i.e only 14 shots taken out of the 36 available) would be unusable forever. Suffice to say that when one put a roll of film in a camera, it was critical to wonder what situation was going to be photographed. I’d rather mention this straight away: if I use the past tense for film photography, it is not to imply the days of film photography are over. On the contrary, there are many amazing photographers out there who loves shooting and develop film and should not be booed for it. It all comes down to personal preferences. Most point and shoot cameras on the market today offer you the possibility to choose an ISO value from 100 ISO to 1600 ISO. For DSLR and professional camera, you can extend the ISO to 12800 ISO or even 25600 ISO. *I know some Nikon camera offer you 200 ISO as the lower ISO available and some professional camera let you even choose 50 ISO. Here is the ISO scale: 100, 200, 400, 800, 1600, 3200, 6400, 12800, 25600. The jump from 100 ISO to 200 ISO (or from 400 to 800) is called a full stop. Some cameras let you use 1/3 stops for more flexibility with your exposure. Each time you increase the ISO value by one full stop, you increase the camera sensor sensitivity, so it captures twice more information from the light. The same logic is applied when reducing the ISO value by a full stop ( the sensor being less sensitive will capture half the information coming from the light). Samples shot with my Canon 60D. These were shot in small JPEG and not post-processed.

What ISO should one use?

Well, it all depends on of the situation that is being photographed. Here are a few rules of thumb that should not be seen as restrictive:

• Sunny, overcast day: 100 ISO.
• In the shade: 200 ISO or 400 ISO.
• In the evening or dark places: 800 ISO and above.

As I said the above should not be seen as restrictive, since in WildLife and Sports photography, a photographer may be using a high ISO even when shooting on bright day light. This will be covered in future episode and post.

High ISO drawback: The Noise

First off let’s clear any doubt. This noise has nothing to do with sound! Noise is a pixel pollution in your digital photography. When shooting film, we would talk about Grain. So where does that noise come from? When increasing the sensitivity of your sensor ( increasing the current that travels through the sensor chip in your camera), the sensor is trying to analyse the information coming from the light while expecting the light does not provide much in that particular situation. In low light situations, noise will be found in dark areas in the photograph. This is because the sensor tried to make sense of the dark areas and rather than giving you a black pixel it might give you a coloured pixel such as blue, green and red.

Some of you may notice some noise in pictures where there are no dark areas in it. Well, when you set your ISO to a high value (i.e. 800 and above) the sensor thinks there is not much light to deal with and “over analyses” the light information blind fully and the resulting image is not as sharp and clean as it would have if the sensor had been set to a more appropriate ISO setting.

Are we doomed?

No! Noise are well expectable/predictable in Digital photography and assessing the situation you want to capture would enable you to choose the most appropriate sensitivity level (ISO setting) for your sensor and subsequently reduce the appearance of the noise phenomenon. In some cases, you are bound to have noise (night photography), and you can either reduce it in post-production with software such as Adobe Lightroom, Adobe Camera Raw and we will review this process in future video and post. Interestingly, the latest camera would offer you the ability to reduce the noise “in-camera” via their High ISO Noise Reduction feature. We will review this in a separate video and post as well. If you have any question, do not hesitate to put it in the comment box below.