You just bought a new DSLR camera and you're really excited to use it. You want to take high quality images that really wow your friends and family, but you're not sure how so you shoot your camera in automatic mode. While taking the camera controls into your hands can be very intimidating at first, it's actually really easy with a little practice.
The exposure triangle consists of three parts (hence triangle): Aperture, Shutter Speed, & ISO. Each of this has its own unique effect on how your final image will look. To keep this short I am going to write a brief summary on each before writing longer articles on each individual item itself.
The A mode on your camera stands for 'Aperture Priority' but what does this mean? Aperture is how 'open' your lens is. The smaller the 'f' number the more open your lens is and therefore the more light that will be allowed into your lens. Usually this is how lens are represented when they are sold (f2.8 24-70mm would mean a constant maximum aperture of 2.8). Often your camera will allow you to use anywhere from your maximum aperture on your lens all the way to f22. As you make this number larger, you are limiting the amount of light that is allowed into the lens. The trade off is that the higher the f number, the more depth of field that your image will have. Images with the soft background or 'bokeh' look are often taken at apertures of f2.8 or lower. For reference most of my landscape images are taken at f8 as this is usually around where the lens is sharpest but still provides adequate depth of field. If you shoot in A mode you will have control over the aperture you want to portray in your image. Your camera will then use this to determine what other settings (ISO & Shutter Speed) are needed to properly expose the image.
The S mode on your camera stands for 'Shutter Priority' mode. This gives you full control over your camera's shutter speed. Shutter speed refers to how long the shutter of your camera stays open. Pending on your camera body the fastest shutter speed you can shoot at is 1/5000 of a second. Using a shutter speed this fast would only be used for truly freezing and instant moment in your image (let's say if you were shooting sports). However this is achievable all the way down to about 1/200 of a second. Shooting portraits is very similar as I would recommend shooting them around 1/200 but no slower with image stabilization. The other main use for this mode is for long exposures (say you want to add motion blur to a shot or shoot car trails at night time). For these sort of shots you need a tripod to ensure you camera is stable and doesn't move during the exposure. Most cameras can shoot up to 30" in a single image (most also have bulb mode which gives you complete control and let's you shoot even longer). At night when there is no light available this is how people often take landscape images (think of the famous car trails shots). Allowing the cameras shutter to maintain open for longer allows it to gather more light in order to properly expose an image. Remember an image sensor is all about how much light is able to get to it in order to properly expose for an image.
Although there is no ISO priority mode on most cameras, ISO is very important to how our images turn out. ISO is how sensitive our sensor is to light. The standard is ISO 100 which is also referred to as base ISO. Doubling this number to 200 would make our image sensor twice as sensitive to light as before. Normally you are not going to touch ISO unless shooting in manual but it is still important to understand. The lower the ISO the less sensitive your sensor is to light. Some cameras will let you shooting below base ISO which allows you to shoot longer exposure images during the day if you wanted to (for example my Sony can go down to ISO 50). However let's say you wanted to shoot a portrait image at night, you could increase the ISO to 800 to account for the lack of light and exposure a faster shutter speed. Raising ISO doesn't come without consequences though. The higher the ISO the more 'noise' you are introducing into an image. Noise is very visible at a certain extent. Noise often looks like what people would call grain.
That's all for our brief introduction on the exposure triangle. Once you have mastered understanding each individual concept you can move into shooting in manual mode (we will talk about this later). This gives you full control over all three concepts in order to portray exactly what you want in your image. If you have any questions or comments about the article or if anything is not clear please feel free to comment below.
Stay true to you.