The main similarity between changing your f-stop to adjust aperture and changing your ISO or shutter speed is that all three will impact the exposure of an image. However, to alleviate any possible confusion about the key differences, refer to the following chart:
We’re sorry if we’ve left you scratching your head, wondering how this all fits together. Let’s use a popular analogy on the topic to get us back on track.
Imagine your camera is a window with shutters on the outside. The aperture is the size of the window (the size of the window dictates the amount of light that’s allowed in). The shutter speed is like the shutters on the window (the longer those shutters stay open, the more light is let into the house). To complete the analogy, imagine there’s a person inside the room wearing sunglasses to represent the ISO (the sunglasses make the wearer less sensitive to incoming light).
Tweaking any of these elements is going to impact the exposure of your image. Furthermore, each time you make an adjustment of your ISO, aperture or shutter speed, you are going to not only impact the exposure, but the other elements, too. Said another way: if you change one element of the triangle, you are going to have to change the others as well to keep the same exposure.
There’s another reason you have to be careful. Making changes to these elements may impact areas other than just the exposure:
- Changing aperture results in a change of DOF.
- Changing ISO can change the noise/grain in a shot.
- Shutter speed affects how motion is captured.
As you can see, playing with each of these settings to get the proper exposure is an art form in and of itself. To master the triangle, you are going to have to experiment and practice.
Thankfully, there’s a shortcut (see the section below on Aperture Priority Mode) you can use while you brush up on your triangle techniques.
F-Stop vs T-Stop
By now, you know a lot about the f-stop, but have you heard about t-stop? It would be understandable if you haven’t because it’s often found on cinematographer’s lenses. Essentially, the t-stop, which stands for transmission stop, is more accurate at determining exposure than an f-stop. This is because each t-stop lens is tested by the manufacturer being sold. F-stops can be off by about a third of a stop (at most), which can be fixed in post-production. However, many cinematographers may prefer a t-stop lens to help save money in post-production.
Aperture Priority Mode
Aperture priority is a semi-manual mode – to use it, turn the dial on the top of your camera to ‘A,’ or ‘Av’. This allows you to select the aperture, while your camera’s computer calculates the shutter speed for proper exposure.
- Use a tripod in case your camera selects a slower shutter speed to eliminate camera shake and allow for a more stable long exposure.
- If you opt to go tripod-less, and the camera selects a shutter speed that’s too slow, you can increase the aperture to compensate. Then, your camera will select a faster speed to correspond with the new aperture you’ve selected.
To Wrap Things up…
We’ve covered a lot of ground in this guide. You should have a good grasp on how f-stops affect your aperture, how to control exposure and depth of field by stopping up/down, and have a solid understanding of the theory behind f-numbers and focal ratios.
If there’s one thing we hope you take away, is that the larger your aperture, the smaller your f-stop number will be. It’s not rocket science, but can take a little getting used to when you want to shoot fast without thinking.
Answers to Exercises:
- f/2.8 lets in way more light than f/16.
- f/10 lets in way less light than f/2.