In this photography tutorial we are going to explain the basics of one of the most important elements of photography: aperture.
What Is Aperture?
The basic function of any camera is to gather light and the aperture is the diameter of the lens that determines how much light eventually falls on the image sensor or film. The whole process works just like the human iris, as the size of the opening is set by adjustable blades that control the amount of light that goes in the camera. Hence, the aperture affects exposure and depth of field (DOF) as further detailed in this photography tutorial.
Calibrated as f-numbers or f-stops, the commonly known ‘relative apertures’ are displayed on the lens barrels in a couple of different ways: f/22 f/16 f/11 f/8 f/5.6 f/4 /f2.8 f/2 f/1.8 or F22, F16, or 1:22, 1:16, etc.
How did we end up using these notations? Well, absolute apertures depend on the focal length. For example, a 50mm aperture diameter on a 200mm lens has the same effect as a 25mm aperture diameter on a 100mm lens.
Every next aperture diameter is 1.4 smaller or bigger than the last one, hence the use of fractions to express them.
What you have to remember is that large numbers (f stops) stand for small apertures and the other way around. Yes, yes – this is where digital photography usually becomes very confusing for beginners.
In reality, things are simple - because f stops are fractions of the focal length, higher numbers represent smaller apertures. Regardless of the focal length, every next f-stop halves the amount of incoming light, as underlined in the graphic below.
Photo source: Google images
• Larger Aperture Number (1.4) = Wider Aperture = More Light
• Smaller Aperture Number (16) = Narrower Aperture = Less Light
Maximum Apertures
While lens apertures can be narrowed without restrictions, the upper limit to how wide a lens can be opened is limited. This limit is called maximum aperture and it’s very important because it pretty much restricts/increases the quality of moments you capture:
a, Under natural light
Both a film and a digital sensor need light to create images. This can be done in two ways, either by opening the aperture as much as possible or by keeping the shutter open for a longer period of time. Flash on is another possibility, but it washes out most of the images, so you should avoid this setting as often as possible.
In the digital photography world, shooting fast moving objects (cars, animals) and persons (kids running, friends riding a bike) require wide open lenses. For these cases a f2.8 lens is more useful than a f4 one. Allowing double amount of light to enter your camera decreases the amount of time needed to shoot subjects in motion under natural light, indoors or outdoors.
b,With fast shutter speeds
It is said that shooting under rain or through windy days makes the difference between a
great and an average photographer. Wide maximum apertures and fast shutter speeds don’t go one without the other and dreadful weather is a great way to test these out.
Beside noticing the spectacular scenes around you, all you need is a shutter speed of at least 1/500. Wide maximum apertures (as f 2.8) grant you the light needed for fast shutter speeds and lets you capture interesting moments like a clear glance of a baby lizard in motion.
c, With reduced depth of field
Wide maximum apertures have shallow depths of field (DOF), allowing you to focus on something special, while leaving blurry backgrounds for a stronger emphasis of your central subject.
Having a lens with maximum aperture of 5.6 for example doesn’t let you reduce the DOF as much as you’d like for perfect portraits or simply stunning nature photography.
When you wade through all the numbers while shopping for lenses you can stumble upon either something like : 50mm f1/8 or something like 18-55mm f/3.5-6.3.
The first set of numbers – 50 mm and 18-55mm represent the focal length (a topic to be detailed in another photography tutorial). The second set interests us the most as they indicate the maximum aperture of a lens.
If the first case is pretty much self explanatory, the second one is a standard example for zoom lenses that have a variable maximum aperture in our case:
• At 18mm the maximum aperture is f/3.5
• At 55mm the maximum aperture is f/5.6
For different lighting conditions you need different maximum apertures. You can use the following as reference:
Words & Pictures Adela Trofin
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