Aperture, in its most basic meaning, is easy to understand. Aperture simply means an opening to let light in. This is fairly straight forward when you ask yourself “what is aperture?” However, the whole explanation of aperture gets very tricky as soon as you introduce f stop into the mix.
We can easily grasp what f stop is and how it works. It is an opening in the lens by which light comes in or is shut out, depending on what f stop you select on your camera. F stop is not only responsible for controlling how much light your image has or not, but it can have an influence on depth of field. I’ll save depth of field for a other day, but lets discover what lens aperture is.
Your lens aperture refers to the maximum amount of light that your lens can let in. Let’s take for example my trusty canon lens I used for much of everyday shooting. The technical name for this lens is: Canon EF 24-105mm f/4 L IS USM Lens. So what does that mean? It means that F4 is the most that the aperture will go to. I have also used a Canon EF 50mm f/1.2 L USM Lens. Look again at the Fstop number. It has 1.2. That means that the most light that the lens can let in is an f stop of 1.2.
So how does this relate to fstops for your single photos? Each time I place the F4 lens on the camera, it means that the maximum aperture my photos can go to is F4. If I change over lenses and place the 1.2 lens on the camera, then it means all of a sudden I can choose F1.2 for each of my images. Each time I change lenses I have a new maximum f stop I can work with.
Your lens is what controls the maximum f stop of each photo you take. You can’t take a photo at F 1.2 if you have an F4 lens. It’s not physically possible. You are limited to what the lens can offer.
There is another factor to consider in the understanding of aperture. That is each lens also has a minimum aperture too. Although in “photography world” we only go on the maximum. Why? Because we want to know how much light we can get with each shot. Lenses that are as high as F1.2 mean that they cannot offer you a minimum aperture of F22. They usually only reduce to F16 or similar. A lens that has a maximum aperture of F4 can reduce right down to F22. ( However, I do have a F3.5 lens that does reduce to F32. This however, is an old film camera. )
Why use a lens that has such a maximum aperture of 1.2? Easy. When you are shooting at night or in very low light, and you want as much light as you can get. F1.2 is really fantastic to us. You no longer struggle with the Fstop not being able to open up any more. This can be frustrating when you are shooting moving subjects in very dim light, such as concerts or street photography. This type of lens is called a “fast” lens. This means you can open up the aperture really wide to allow for faster action to take place.
With a fast lens such as F1.2, you can easily work with ISO 100 or 200 in low light conditions without having any noise or grain ruining your indoor photos. I find this kind of lens a joy to work with in low lighting conditions. It’s simply so much fun!
Before this gets really confusing, let me simplify it. Your lens aperture is the maximum aperture that the lens will open up to. Then, you will only be able change the f stop as far as the maximum aperture of the lens. In other words, each time you take a photo, you won’t be able to widen the aperture anymore than the lens will go.
This is exactly why we have different lenses for different things. For example, a studio portrait photographer will be able to work very well with F 4. The lighting is abundant and well controlled. An events photographer for rock concerts will find that F4 is just not enough. She may need a lens that widens to F2.8 or 2.0. A photographer who wants to shoot city scenes at night will find that f1.2 is a nice wide size for interesting skylines and sharp reflections.
So what is the best lens to use? A fast or slow lens? The answer is that it depends primarily on what photography you do. If you are a landscape photographer then F4 might just be suited to your needs. If you shoot parties and sports photography, you may find that you need more light and opt for a lens that is around F2.8 or 1.8.
Either way, the lens aperture tells you what maximum aperture you have to work with for each individual photograph you take. It is always advisable to choose your lens carefully before buying. And if you are unsure, then choose a lens that is the middle of the road like an F2.8.