The Exposure Triangle
We are in mid-September and it's time to go back to school or to our work routine. The best way to roll up our sleeves is to get our favorite camera, taking advantage of Aclam’s Weekend Promotion or student discount, and start shooting. But it's always good to refresh your memory after the summer and go over the most basic concepts to keep them very fresh. And one of the most basic and necessary is the exposure triangle.
The exposure triangle is one of the most fundamental tools of photography. It’s a direct relationship between the three main actors in the exposure: the aperture, the shutter speed and the sensitivity. These control the entry of light that will reach the final image, but depend on different factors to achieve it. This means that, depending on the situation in which we find ourselves in, we will have to give preference to one or the other.
In first place, the aperture is the opening of light that the lens lets in. It’s measured in f-numbers (f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, etc.). The larger the f-number, the more closed the aperture and the less light passes through the optics. One of the most interesting main properties of working with a more open or enclosed aperture is the focused space of the image - which is called depth of field. For example, working in very open aperture like f/1.4 the image we obtain will have a very small depth of field, therefore we will have very few elements of the image focused. It is very common to rent very bright photography lenses, like the Zeiss Milvus or a 50mm lens, to get the bokeh effect or a very blurred background. On the other hand, with a very closed aperture like f/22 we will be able to have a very wide depth of field, and to be able to focus objects to much distance between them.
Bokeh and low depth of field achieved with a very open aperture.
Next, the second exposure tool is the shutter speed, which is the amount of time the camera lets light through. This means that the longer the shutter is open (the slower it is), the more light the image will have, and conversely, the faster the shutter goes, the less light will reach the final image. As a unit of time it is measured in seconds or fractions of a second (2", 1", 1/2", 1/4", 1/8", 1/15", 1/30", 1/60", 1/125", etc.), being 2" a slow speed and 1/1000" a very fast speed. The main feature provided by shutter speed is the time the object needs to be static in order to be correctly captured in the image. At very high speeds, the camera can freeze in the image objects that move very fast like people running or cars. It is very common to shoot at very high speeds for sporting events or documentary photography of nature. On the other hand, at low speeds, for example less than 1/125", moving objects can start to become blurred or, in case they are very fast, can only be seen as curtains of motion. Even the camera movement itself can blur the entire image as in the panning effect or, with a static camera; moving light objects can create the light painting effect.
Frozen object with panning effect achieved with relatively fast shutter speed while panning the camera.
Light-painting effect achieved using low shutter speed.
Finally, the last tool of the exposure triangle is the sensitivity or ISO. This determines the amount of light that the sensor is able to capture and is expressed in ISO units (50, 100, 200, 400, 800, 1600, etc.). When the ISO is very low, the amount of light the sensor captures is low and the higher it is, the more light it captures. Sensitivity is a very delicate factor to touch because, although it can be very helpful to have a very high ISO in very low light conditions, it creates one of the least desirable effects: noise. This is why it is very common to work with low sensitivities such as ISO 100 or 200 and only resort to higher ISO in extreme cases. Even so, the technological advance allows the manufacture of higher quality sensors, and it is very common to find photographic cameras with very high sensibility such as Sony a7s II and a7r II for rent.
Image where noise is appreciated because of working at high ISO.
Taking into account these values, and working the conditions we prefer in each case, we can always get a perfect exposure. For example, in situations where speed is key, we will give preference to shutter and play with aperture and/or sensitivity; in situations where we prefer a specific aperture, we will play with shutter and/or sensitivity; and in situations where noise is our weakness, we will have to play with shutter and/or aperture. Once you master these three actors of exposure, you will be able to obtain the best pictures.