How Does Aperture Priority Work on My Canon Rebel T6i?


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I use Aperture Priority for most of my shooting. I have my camera set to this pretty much all the time. I prefer this setting because it gives me a very simple method for controlling the light that comes through my lens, without having to concern myself too much with shutter speed or ISO. Of course, I need to take those other two factors into consideration when I'm photographing (shutter speed first and then ISO), but in general, I like to play around my aperture the most.

If you aren't aware, a lens's aperture primarily controls two things. First, as I said above, it controls how much light passes through the lens to your camera's sensor. It also controls how much depth-of-field a photograph will display. Before I go any further with this post, I think it would be wise to explain more of what I just mentioned.

The aperture size inside of a camera lens is controlled by very thin plastic or metal fins that move. When you set a larger aperture, the fins move out of the way, allowing more light to pass through into the camera. When you set a smaller aperture, those same fins move into the way of the light, obstructing it, so a smaller amount of light passes through to the camera. It's a fairly easy concept to understand. What's confusing about it is the numbers that are assigned to aperture values. Get this: the lower the number, the larger the aperture setting that allows more light to pass through. The higher the number, the smaller the aperture setting that allows less light to pass through. So, an aperture value of f/1.2 would let a heck of a lot more light through the lens than a value of f/16. The f/1.2 hole is much bigger.

There are a few different ways to think about aperture to make the whole idea more clear. I'll explain one right here and then another below. I don't want to go crazy far into anything, but I will need to explain how aperture impacts shutter speed.

If you are using a small aperture setting for your lens, you're not letting a lot of light through to your camera. Because of this, your shutter speed needs to slow down to compensate. No matter what you do, your camera needs a certain amount of light in order to properly expose a photo. So if you limit the light through the lens, the shutter will need to stay open longer to capture the light it's looking for. If you open up your aperture as far as it can go, the camera will recognize that and hasten the shutter speed.

If you pretend that you're standing next to a swimming pool that needs to be filled, you'd most likely need to make a decision as to what you're going to use to fill it. If your options are a garden hose or a fire hose, you can probably imagine how different each would be. No matter which filling method you choose, the pool will need to be filled. Consider the full pool the same as a properly exposed photograph. Both need to be completed. They're the ultimate goal. A full pool and a nice image.

Consider the filling method the aperture. A garden hose is a small aperture and a fire hose is a large aperture. If you use the garden hose, it's going to take a very long time to fill the pool. If you use the fire hose, it's going to take a shorter time. While the hose sizes are comparable to the aperture, the time it takes to fill the pool is comparable to the shutter speed. So, you can see how each has an effect on how the pool gets filled.

Of course, there's a lot more than goes into all of this, but what I just explained is the basics.

Another aspect of photography that is impacted by aperture size is depth-of-field. All this is is how much of the final photo is in focus. I'm sure you've seen photos where the object in focus is sharp, while everything behind that object is soft (or blurry). This is directly related to aperture size in the lens. A large aperture size will offer a more shallow depth-of-field (more blur behind the point of focus) and and small aperture size will offer a more deep depth-of-field (less blur behind the point of focus). You can remember this by thinking about the bigger numbered aperture setting (smaller hole) as giving you a bigger area of focus. The smaller numbered aperture (larger hole) will give you a smaller area of focus.

Okay, let's get to the meat of this post. I simply want to show you how to set your Canon Rebel T6i, or any Rebel for that matter (T2i, T3i, T4i, T5i and T7i) to Aperture Priority. It's so easy.

Take a look at the dial on the top of your camera. You should see a bunch of different settings. The ones I'm primarily concerned with here are the P (Program), Tv (time Valuation (Shutter Speed)), Av (Aperture Valuation) and M (Manual). All you need to do to set your T6i to Aperture Priority mode is to turn the dial so the Av setting is aligned with the small white tick mark on the camera itself. After that, you'll need to use the dial on the top of your camera to choose the actual setting you'd like to shoot with. Learn more about Aperture Priority here. There's tons of good information in that post.


Please let me know if you have any questions about what I shared today. I know the aperture settings are different for all makes and models of camera, but this ought to help some folks who use the very popular Canon Rebel series.