I have decided to write a few articles on the most basic aspects of photography, which will become natural as you start mastering this art. However, I remember struggling with them when I first started – and I guess that most of us have a similar experience.
Today, I am going to discuss the final component of the exposure triangle: ISO. By mastering ISO, aperture and shutter speed, you will be able to photograph in any conditions, at any time of the day and in any shooting mode.
Exposure Triangle, photographylife.com
ISO represents the sensitivity of your camera’s image sensor. The lower the ISO, the less sensitive the sensor and the more light it requires in order to expose adequately. Moreover, the lower the ISO, the finer the grain in your pictures – which you might better know as noise. On the other hand, by increasing your ISO, you will be able to use a smaller aperture and a faster shutter speed. Every camera model has a native ISO, which describes the minimum and maximum ISO figures of that specific camera. Often, the lowest ISO is 100 and the maximum varies depending on the how professional and new your camera is.
What about Film Photography?
The same concept applies to film photography as well. When talking about the sensitivity of the film, we talk about ASA instead. Of course, every film will have a preset ASA, which represents the suggested ASA level to expose that roll. However, you can either increase or decrease that figure and use the film accordingly. For instance, I love purchasing ASA 400 films and if photographing at night, I can expose the roll as if it was an ASA 1,600. This allows me to use a faster shutter speed and avoid camera blur.
As a rule of thumb for film photography, I would suggest to never increase or decrease the native ASA by more than two stops. This means that if the native ASA of your film is 400, you should not expose it at more than ASA 1,600 or less than ASA 100 in order to avoid unusable grain to pop up. Moreover, it is really important to expose the whole film at the very same ASA. Otherwise, when developing it, some pictures might result exposed wrongly.
ISO in Street Photography
As I said in previous articles, the key of street photography is being as responsive as possible in order to capture the decisive moment. This means, using settings that will minimise camera blur and render a sharp photograph. These two factors are directly controlled by shutter speed and aperture. So you could start photographing using an ISO low enough to avoid grain, set aperture to the optimal figure for your lens and control the light using your shutter speed. However, when you realise that you cannot keep decreasing your shutter speed without incurring in camera blur – this happens at night for instance – you can start increasing the ISO. If this is still insufficient, you can start opening your aperture up to allow more light to hit the sensor.
Generally speaking, when making street photographs during the day, I like to start by using ISO 400 and use the shutter speed to manipulate light. At night, I do not like to boost ISO over 1,600 as I do not like too much grain in my photographs. Therefore, I rely on a wider aperture to keep photographing.
Remember that if you use a sturdy surface – or even a tripod – for your photographs you can decrease the ISO in order to get rid of the unwanted grain. Indeed, a steady enough surface will allow you to decrease the shutter speed without introducing camera blur. This is important to remember to render crisp long exposed cityscapes.