One of the first concepts learned when diving into the world of manual photography is the relationship between the big 3 settings: aperture, shutter speed, and ISO. There are many other important settings that a camera operator should know, but these are the main 3 that will affect what kind of raw image you will be getting. Each of these settings has its own unique impact on the final image, but they all work together to affect the amount of light that reaches the sensor and, depending on the settings, can result in wildly different creative outcomes.
Shutter speed is the most obvious of the 3 as to what is being affected: how fast the shutter is clicking. It is measured in a fraction of a second, but most cameras list it as a single number for ease of reading. So if your shutter speed is showing on camera as 50 what this actually means is 1/50th of a second. This seems really fast, however, in handheld photography, the lowest shutter speed recommended is 1/60 or else new photographers won’t be able to get a clear image due to hand shake. Now that we know what shutter speed is measuring, let’s talk about how it affects the final image; the faster the shutter speed, the less movement you will see in your final shot. Think about any sports photo you’ve seen. They typically have no motion blur because they are shot with a very fast shutter speed. Have you ever seen a night sky photo where it looks like the stars are lines in the sky? This is because the photographer used an extremely long shutter speed in order to capture the star movement across the night sky as the earth rotates. Shutter speed is an important variable used to impact the creative outcome of any photograph, but in video it is significantly less flexible. Typically, video is shot in either 24 or 30 frames per second (fps). Slow-motion footage (also known as high-speed footage) is shot in 60fps or higher. This is important because the shutter speed is directly tied to the fps of a clip and should always be double the fps. So if you are shooting in 24fps then your shutter speed should be 1/50, if you are shooting in 60fps then your shutter speed should be 1/120, etc. When these two settings slip from this relationship, the final image tends to have an unpleasant stuttering effect as if the frames are sticky.
ISO stands for International Organization of Standardization. This setting, however, doesn’t actually refer to the organization itself, but the sensitivity to light. This setting is also referred to as film speed and if any of you were into film photography, you will remember that when you purchased a roll of film it had the speed listed on it. Film speed has also been called ASA and DIN in the past. These were combined together to create ISO, but they all basically had the same meaning: how sensitive is my sensor or film to the light coming in? ISO speeds are measured as whole numbers and on digital cameras can range anywhere from ISO 50 up to ISO 4,000,000! Not only does it affect the sensitivity to light, but it also affects the amount of grain that can be seen on the final image. A lower ISO will have very little or imperceptible amounts of grain, whereas a higher ISO speed will result in a grainy look to your image. Creatively, this can be an interesting effect to add to a shot depending on what you want the final image to look like. However, with the many advances in post-production software, if you don’t shoot to have film grain in your original, you can add it in while editing. On the flipside, if your photo has more grain than you wanted, it can also be smoothed in post, but it isn’t quite as quick of a fix as adding grain.
While shutter speed and ISO are settings that are camera-based, aperture is a setting that is dependent on the lens you have on the camera. The aperture size is often referred to as lens speed, and the lower the aperture a lens can achieve, the “higher speed” the lens is. Aperture is measured in f-stops: the ratio between the diameter of the lens opening and the focal length of that lens. This affects how much light ultimately comes through the lens and lands on the sensor of the camera. Aperture tends to be the setting that new photographers have the most trouble understanding because the numbers are counterintuitive. With shutter speed the larger the number, the faster the shutter click and with ISO the larger the number, the more sensitive the sensor is to light. However, with aperture, the smaller the number the larger the lens opening; an aperture of f/1.8 is much larger than that of f/22. The way aperture affects the end result of an image is through depth of field. The larger the aperture the lower the depth of field of an image. So if you are wanting an artistic image where only a small portion is in focus you will want to use an aperture of f/4 or larger. If you are shooting landscapes or commercial stock footage, typically you will use a very small aperture of f/10 or smaller to capture the details across the whole horizontal plane of the image. When shooting interviews, there is a depth of field line that needs to be walked. It is pleasing to have the background of the subject blurred out, but if you have too large of an aperture your subject might fall out of focus when they lean forward or backwards slightly while speaking.
How they work together
We’ve learned how each of these individual settings affect the light hitting the camera sensor, and the creative properties of each setting, but how do they work together? First you have to decide the look you are going for and base your settings off of that creative vision. Say you want a long depth of field and no motion blur. You start with a fast shutter speed to stop the motion of your image, then you choose a small aperture so that the depth of field is across your whole image, then based on these settings you would adjust your ISO in order to properly expose the image based on these other two settings. Once you find a combination that is exposed properly you can create a chart of exposures to quickly and easily adjust to change the look of the final image. Aperture and shutter speed can easily be adjusted together. If you increase the shutter speed by one stop you can simply decrease the aperture by one stop and the image should remain exposed perfectly. There are many combinations of these three that can result in a properly exposed image. Ultimately, you need to decide which path you are going to take to get to an exposed image that fits your creative vision.