It dawned on me yesterday that I’ve written about shooting modes, and I’ve written about exposure, but I’ve never written about how and when you might use certain modes. Treat this topic as if you’ve just moved from full-auto or program mode, into aperture priority, and I’ll walk you through everything you need to know.
Full-auto mode allows you to change only the image format, and the burst fire mode. It will even use the pop-up flash if it thinks it needs to. Program mode is similar to a priority mode, in that you can change the likes of metering, white balance, etc., but you can’t change the shutter speed or aperture (you can change the ISO). OK, now we’ve seen the difference, lets have a look at what it can do.
When you switch to aperture priority, it does exactly what it says on the tin. The exposure gives priority over the aperture setting, and then shutter speed adjusts accordingly. Lets say that if you set the aperture to f/8, and the shutter speed is 1/200 of a second, and you decided to widen the aperture to f/5.6 (which allows twice the amount of light in), the camera will automatically change the shutter speed to 1/400 of a second to counteract for the extra light. This is how priority modes work.
I use aperture priority mode about a third of the time (along with shutter priority and manual for the other two thirds), and it’s good for a number of reasons, the three main of which being sharpness, depth of field and light.
- When you widen the aperture to a lower number, say f/2, then you allow much more light into the lens, which allows you to speed up the shutter speed.
- Wider apertures also mean there’s a shallower depth of field and vice versa.
- When you narrow the aperture to around f/8-11 this is typically when the lens will be at the sharpest.
As you can see, there would be plenty of situations where you might want to use aperture priority over shutter or even manual. But what about all those people who say you should only shoot in manual? Well, they’re wrong. At least that’s my opinion. There’s plenty of cases where you might want to choose manual, but that’s only about a third of the time for me. Lets have a look at some of the situations where you would want to use aperture priority.
First though, I feel it’s worth mentioning an advantage that aperture priority has over shutter priority when it comes to exposure. A longer exposure will always allow more light into the lens, but not necessarily at speeds which will allow you to hold the camera in your hand. When it comes to aperture, it’s to do with the hardware of the lens, so if you buy one with a wider aperture, you can keep the shutter speed at handheld speeds, while widening the aperture to allow more light in. It’s a good way to improve the performance of your camera.
When you should use Aperture Priority Mode
Situation 1 – Good light / Sunny day
When the light is fairly constant, you could use manual mode, but chances are that you’re just creating extra work for yourself. Why make the small changes that the camera is going to make for you? If you want to change the exposure, you can do so with exposure compensation meter provided in the camera.
When the light is good, you don’t need to worry about blurring your images because the shutter speed is always going to be fast enough to capture the movement. Particularly if the light is good. There’s an old rule ‘sunny 16′, which suggests a narrow aperture for shooting in the sun, and it really works. Just another reason to shoot in aperture priority.
In good light, you’re rich with light, so you might as well use a lot of it by narrowing your aperture to produce sharper images.
Situation 2 – Portraits
When shooting portraits, whether you’re using flashes or natural light, the lighting is usually pretty good. We tend not to make things harder for ourselves than they need to be, so comfortable lighting situations mean that we can take the photos at the aperture of out choosing.
I personally like to shoot at a range of apertures when taking portraits, but f/8 is one of my favourites. I just find that my photos come out the sharpest at this aperture, which works great for portraits.
Situation 3 – Landscapes
Landscapes typically have a foreground and a background, and often a middle ground too. To see all of this in focus, you need a wider aperture, somewhere up to about f/16 works for me. There are times where I will use a tripod, and if I am then I might use manual mode, but more often than not, I’m using my camera handheld so aperture priority works fine as I’m not playing with any longer shutter speeds. This is where depth of field becomes really important.
Situation 4 – Shallow Depth of Field
Shallow depth of field is achieved by opening up your camera’s aperture, which allows more light in at the same time. It’s not a small amount more light either, it’s a lot more light. The jump from f/2.8 to f/1.4 allows four times more light in, which can easily be counteracted by the shutter speed automatically, in aperture priority mode.
When you change the DoF, chances are you will be experimenting quite a bit, so you’re just giving yourself more work if you’re using manual mode. It’s not all about manual mode.
When you Wouldn’t Use Aperture Priority (But think you might)
Situation 1 – Poor light / Darkened room
As I mentioned before, the beauty of a wider aperture is that it allows your camera to see more light, and this is especially true in a darkened room. But that doesn’t mean you should select aperture priority mode. I find it best to use shutter speed priority. Let me explain…
When you’re in low light, the two main worries are about exposure (not getting enough light) and camera shake (blurry pictures). If you set the camera to aperture priority then you’re only really dealing with half of the problem, which is light. When you’re in shutter speed priority, you can account for the camera shake (say, 1/30 or 1/50 of a second) and the aperture will adjust around the speed to produce the exposure.
Even if there’s not enough light, the aperture will automatically go to it’s widest, and you can play with the photo in post production. At least that way you don’t have a blurred photo, which you can’t fix (yet).
Situation 2 – Night Landscapes
I know I mentioned above that I like to shoot landscapes in aperture priority mode, and this is true, but not when I’m shooting at night. Night photography is a different game, reserved for the likes of manual mode. The lighting becomes so unpredictable, you have to make calculations and estimations in your head, it’s really more a case of trial and error.
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When you’re shooting indoors, there’s a lot less available light so bouncing flash off a wall and shooting with a wide aperture, creates just the right amount of light to create an good exposure.
When your aperture is wide open, your depth of field is really shallow and it’s hard to find a good focal point. You can either really worry about this or not worry at all. In the photo below, shot at f/1.8, the lack of focus actually makes it look better in my opinion. 
Shallow DoF helps to draw the attention to a certain part of the body, and leaves the rest blurred.
When you have mutltiple subjects in a scene, a wide aperture will only focus on 1 person, making it a great tool for selective focus in photography.
The photo below was shot wide open, which kept the background blurred, even though the subject wasn’t far away from it, and that makes the photos look a little eerier in my opinion. 
To emphasise the DoF, place the subject in the scene moving away from you.
Shot in twilight, the wide aperture allowed me capture loads of natural light in the background that I wouldn’t have captured otherwise.
Be very careful where you’re focusing. Rather then focusing on her nose, I focused on the light on her cheek, underneath her sunglasses because that produced the best overall focus. 
Natural light if your best friend when shooting with a wide aperture. 
You can be more adventurous with placement of key features in a photo when you’re using a shallow depth of field, as the eyes will be drawn to whatever’s focused.
A wide open aperture is important when you’re shooting into the sun as the lens flare will be the same shape of your aperture, and anything other then wide open will cause the bokeh to be the shape of the aperture rings (usually pentagon or octagon).
Wide apertures are great if you want to viewer to only look at a single part of a photo.
Top Tip! If you focus on the eyes of a your subject, the rest of the face will appear in focus too, even at f/1.4.
Wide aperture allows you to capture loads of light, which means you can turn up your shutter speed and take photos while you’re walking, of other moving subjects.
If there’s movement in your photo, focus on the most still part of the photo, like the lips in the photo below. 
Wide apertures are particularly effective if you’re shooting through objects in your foreground as it turns them to a soft blur.
If you’re going to be shooting with a wide aperture, consider what else you can put on that same focal plane and have multiplie points of interest in the photo. Not only was the camera focused on the model’s face, but the flowers she was reaching for too.
