How to: Understand Photo Exposure Triangle
There are 3 parts to the exposure triangle. Do you know them off the top of your head? Let's dive in and talk about the exposure triangle and how to use it creatively.
What is blowout?
An image is composed of data. If your exposure is too high, your camera is not capable of capturing the data and will represent the missing data as a blowout, a "hotspot" in your image. The same is also true for the opposite end of the light spectrum. Too dark, and your image will have just a black spot. Consider the image below and how little information the image provides our brains. To make this illustration, I adjusted the light curve to show what a highlight vs a low light is. The image below is what we, as photographers, are trying to avoid.
ISO or ASA
ISO, or ASA on older film cameras, refers to how sensitive your film or sensor is to light. The higher the number, the more sensitive the film is to light. Keep in mind that the higher the ISO, the more noise will be introduced to your image. Notice the "static" in the image below? This is the side effect of a high ISO. There are ways to adjust the image to reduce the static, but it's not always possible. Sometimes, you'll need to push your ISO higher if you don't have a tripod to accommodate a longer shutter speed or when you need to capture a moving object at night. Try to keep your ISO under 400. The image below has an ISO of 800. The Sony A7RIV has a native ISO range between 100 to 32,000 and has an extended digital range of 50 to 102,400. With cameras like this, you really need to keep an eye on that ISO value.
F-stop refers to the aperture or pupil of your lens. In an interchangeable lens, you have what are called aperture blades. The aperture of the lens acts like the pupil in your eye. The wider the pupil, the more light is introduced. Ready to be confused? Great. An example of a high f-stop would be F/2, while a low f-stop would be F/8. Notice how I have these values written as a fraction? F over 2 or F over 8. That's because f-stop is a fraction. It tells you how open your aperture is. So, an F/2 means your lens is 1/2 open while F/8 means it's only open 1/8th open. The "f" in f-stop stands for focal length. A lens that's F/2 means it has a very shallow focal length or depth of field while also having a large opening for light to pass through to your sensor. Generally speaking, you are always looking for a high f-stop lens, F/2 or better. The drawback of this part of the triangle is limited depth of field may not always be desired and high f-stop lenses can cost a thousand plus dollars, like my 24-70 mm lens. Referencing the image below, notice how the letters on the wine bottle PRIMA are tack sharp, but the rest of the image is blurry? We want this effect to draw your viewer's eye to your subject, but if your subject is a landscape, you don't want a shallow depth of field.
Shutter speed is how long your shutter is open. The longer your shutter is open, the longer your film or sensor is exposed to light, which creates a brighter image. The plus side of increasing your shutter speed means you can capture more light without introducing the noise that ISO produces. The drawback here is if you don't have a tripod or trying to capture a moving object, you'll have a ghosting effect. This is great for capturing silky waterfalls or light painting, like the pumpkin picture in the introduction, but can be difficult to capture if you are in a bright environment. If you find yourself trying to capture a waterfall at high noon, but still want a silky smooth waterfall, drop your ISO as low as possible, bump up your F-Stop, and you may need a neutral density filter to help the image along.
Practice makes perfect to get the desired effect for the photo you want to capture. If you want to capture motion trails, let that shutter open, step up your f-stop, and drop that ISO. Image too dark and background too blurry? Pick up your ISO and stop down your f-stop. The great thing about digital photography is being able to practice and immediately see what you shot. If you are shooting analog film, you'll need to put more thought behind your exposure triangle, which makes film so much more fun and engaging than digital photography. Get out there and play!
I hope you enjoyed the good (and bad) photos from my collection in this blog. I also hope it provides some clarity behind how to properly expose your photo to get the most out of your camera. If you have a topic you'd like me to cover, drop a message in the comments below.