Each post in this series builds on information discussed in previous posts. See the Photography for Beginners page on the menu for links to all the posts.
In this post I’m going to discuss shooting in Aperture Priority Mode, usually designated by an A on your camera’s mode dial (if it has one).
What is Aperture Priority Mode?
In Aperture Priority Mode you make lens aperture your priority in how you choose to expose an image. You select which aperture you want to use and the camera will automatically choose the appropriate shutter speed to go with it.
You can also choose to select which ISO to use, or you can set ISO to auto and let the camera decide that for you along with the shutter speed. (For more discussion about setting ISO vs. auto ISO see Part 3 in this series.)
When should you use Aperture Priority Mode?
When the effects of aperture size will have the most impact on your image.
Shutter speed is straight forward and almost entirely related to motion blur, either avoiding it or using it. By comparison aperture is quite complex. It will often have the greatest influence on the overall look and impact of your photos.
This is why Aperture Priority is the camera mode typically used most often by most photographers, from beginners to experts.
F-Stop Scale
I don’t want to bog this post down going into details of what f-stop numbers represent physically and mathematically, so I’ll point you to this Wikipedia article if you want to dive deeper.
As a basic starting point, lens aperture sizes are represented by an f-stop number, like f5.6. Which f-stops you have available to you depends entirely on your lens. Lenses vary greatly by model.
The most commonly used full f-stops in general still photography are: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32.
Most digital camera lenses not only include the full f-stops, but break each stop into thirds. So you can use in-between f-stop numbers like f7.1 or f3.5 in order to fine-tune exposure.
A budget point and shoot camera lens might only go from f4 to f8. An advanced bridge camera with a fixed lens might go from f2.8 to f8, or even to f16. Usually you need an interchangeable lens camera (ILC) to get access to lenses with the largest and smallest apertures.
You have to work with what you’ve got. The only time you should spend energy thinking about what you could do with apertures unavailable to you is when you decide it’s time for a new camera or lens.
The thing to remember for exposure is that each full stop on the scale halves or doubles the amount of light. So if you go from f8 to f11 you are reducing the amount of light coming in through the aperture by half. If you go from f8 to f5.6 you are doubling the amount of light.
Variable Aperture
If you have a zoom lens there’s a good chance it has what is called a variable aperture. A variable aperture means that the largest aperture you can actually use depends on your focal length. At the lens’s widest angle (zoomed all the way out) the largest aperture can be used. But the more you zoom in the smaller the largest available aperture becomes.
The f-stop range listed for a zoom lens shows the range for the largest aperture. A budget lens might have a f3.5 – 5.6 variable aperture.
The lenses on my previous and current cameras are f2.8 – f4, which is very good for a variable aperture zoom lens. When shooting with no zoom I can use f2.8. When zoomed in all the way I can only use f4. (There’s a sliding scale, so zoom amounts in between will use f-stops in between.)
Some zoom lenses have a constant aperture. So an f2 constant aperture zoom lens has the f2 aperture available no matter how much zoom you use. Such lenses are quite a bit more expensive, and are also usually larger and heavier.
Quantity of Light
The most obvious purpose of choosing aperture size is to control how much light enters the camera to expose the sensor.
In bright light you often need to “stop down” to prevent overexposure. This means setting your aperture to a smaller size (larger f-stop number).
In dim or dark conditions you need a large aperture to gather as much light as possible when shooting hand-held. If you use the largest aperture on your lens it’s called shooting “wide open.”
Note: Don’t forget that the f-stop scale feels backwards. Small f-stop numbers = large apertures. Large f-stop numbers = small apertures.
Image Quality
Aperture size can affect image quality (IQ).
With most lenses there is a tendency towards soft corners in a photo when using the largest aperture. With many budget and even some mid-range lenses this softness can be seen in a greater portion of the image. To get a fully sharp photo you usually need to stop down one full f-stop, sometimes more.
Using very large apertures can cause noticeable vignetting (slight darkness in the corners of a photo), especially with wide-angle lenses.
At very small apertures light diffraction becomes an issue. I don’t want to go into what light diffraction is here, but you can find photography related articles about it online if interested. In practical terms what you need to know is that the smaller your aperture the more diffraction can affect your photo.
Diffraction can make details look less distinct. With most lenses it’s not much of an issue through f16. Going smaller than that makes it less likely you will get a tack sharp photo.
If you mostly post images on the web or don’t make large prints, diffraction will be barely noticeable even when using very small apertures. For professional work or when wanting to make large prints it’s something to be more concerned with.
Camera lenses have a “sweet spot.” This is the aperture at which you get the sharpest photos because you avoid the negative effects of the largest and smallest apertures. It varies by lens design and model but is usually somewhere between f5.6 to f11.
I discovered the existence of my lens sweet spot by accident. I didn’t know it was an actual thing for all lenses until reading about it later on. I kept wondering why some of my photos had so much better detail retention than others, so spent time comparing the metadata (recorded ISO, shutter speed, f-stop, etc.) of my image files, and realized my sharpest photos were taken at f8.
This is an example of how you can learn as much about photography by closely studying your own photos, both the good and the bad, as you can by reading and watching videos.
Depth of Field
Depth of field (DOF) is one of the most important aspects of photography, and aperture size directly affects DOF. This is the main reason Aperture Priority Mode is the most commonly used camera mode.
Because DOF is a complex topic of its own I’m just glossing over it here. My next post in this series will be entirely about depth of field.
DOF refers to the portion of the photo in front of and behind your subject that is acceptably in focus.
How much depth of field you have to work with depends on several variables. One of them is aperture. In general, large apertures provide a shallow (short, small, narrow) DOF. Small apertures provide a deep (large, long) depth of field.
So as a starting point for a beginner, if you’re taking a landscape photo you generally want to use an f-stop between f8 and f16 to get as much in focus as possible. If you want to isolate a subject by having it in focus and the surroundings slightly to very out of focus use an f-stop of f5.6 or larger.
There are exceptions and variables to what I just said that I will cover in the DOF post.
Bokeh
Bokeh is related to DOF but I want to cover the term here.
Bokeh is an English alteration of the Japanese word boke, which means blur or haze. You will find it’s pronounced at least two different ways. One is the same as bouquet (like a bouquet of flowers). The other is more like it looks, starting with boe and the ending being an eh or uh sound.
Bokeh refers to very out of focus portions of an image, usually behind the subject. How the out of focus areas are rendered in an image varies by distance from subject, lens focal length, and the qualities of a lens.
There is good bokeh and bad bokeh. Really good bokeh is often referred to as creamy because the out of focus portion is blurry in a smooth and appealing way. Bad bokeh looks junky with poorly blended shapes and double lines.
Good bokeh can dramatically enhance the artistic quality of a photo. In addition to being visually pleasing it is used to isolate your subject so it immediately attracts a viewer’s eyes. It prevents background clutter from being a distraction.
Using a wide aperture helps with getting good bokeh.
A trick for getting okay to good bokeh even if you don’t have a quality lens is to stand back from your subject and then zoom in to frame your composition. The longer the focal length (amount of zoom) you use, the easier it is to get good background blur. The more distance there is between your subject and the background also helps
Sun Stars
You’ve seen photos that are shot towards the sun where you can see distinct rays radiating from the sun in a star shape.
You can get some of this effect naturally by composing your image so the sun is partially blocked by the edge of something like a leaf or rock. But the rays won’t be very distinct.
In order to get a distinct and dramatic sun star you need a lens with very small apertures. Usually using an f-stop of f16 or smaller will give you a good sun star.
Shooting into the Sun
Speaking of shooting directly into the sun, you need to be careful. It is possible to damage your camera’s sensor. If you allow too much direct sunlight into the camera it can get fried.
So when shooting into the sun don’t use a wide aperture. Use as small as you can get away with for the image you’re making.
In early morning and late afternoon the sun isn’t as intense, so it’s much safer to shoot into the sun at those times.
As an added tip, never leave your camera in the car outside of a bag without its lens cap on. Even with the camera turned off, if direct sunlight is entering through the lens for an extended period of time it can damage the sensor. A lot of photographers have discovered this the hard way.
Take Multiple Photos
It’s easy to forget to change your aperture when you switch to shooting a different subject. It’s also easy to misjudge which aperture will produce the best results, especially with close-ups.
The trick to coming home with more keeper photos is to take more than one photo of what’s most important to you. Take several photos of your subject from different angles, set your focus point in different spots in the composition, and use two or three different f-stops. There’s a good chance at least one of the photos will stand out from the rest.
This is most important if you are on a once in a lifetime trip or somewhere distant from where you live that you won’t get back to often. It’s so disappointing to be excited about a photo you took, only to get home and realize it didn’t turn out the way you expected. If it happens at a nearby park you can go back and try again. If it happens in another state or country you’re sunk.
It’s better to deal with the tedium of sorting through and deleting a bunch of photos than it is to have only one and discover it didn’t turn out right.
Aperture Priority Mode Exercise
Set your camera to Aperture Priority Mode.
Shoot the same exact composition over and over, changing aperture before each shot from the largest to smallest, until you’ve used the full range of f-stops available on your lens.
You only need to use the full stops for this, not the third stops in between.
Make sure your focus point (usually the middle point in your viewfinder) is on the same exact spot each time you shoot.
Do this with different types of scenes and subjects. Try a couple landscapes and try a couple close-ups. For landscapes include objects at near, middle, and far distances in the frame.
Load your photos onto your computer and using the details or info option on the menu of your image viewing program look to see which aperture was used in each image. Compare the images to see how aperture size affected the end results. Zoom in some to get a good look when needed.
Things you are looking for:
* How does aperture size affect sharpness of details?
* How does aperture size affect how much of the image is in focus?
* Can you detect your lens sweet spot?
This is the kind of exercise you can repeat periodically as you learn more about photography. Things that may not sink in the first time due to information overload might finally click later on.
Many of the effects of aperture choice are subtle. It takes practice and experience to learn the full extent of how choosing aperture can enhance the artistic quality of your images. I still have a lot to learn myself!
Examples
If you’d like to see a post with several examples of how playing around with aperture can affect the look of your photos see this post at the pamphotography blog.
While you’re there you might want to subscribe to their blog. It’s a husband and wife photography team who venture out together to all sorts of places. They post beautiful photos and usually add a couple comments about technique, composition choices, etc.
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