Aperture priority mode allows the user to select the aperture while the camera sets an appropriate shutter speed. Aperture priority is often abbreviated as "A" or "Av" on camera mode dials.

Let’s tackle shutter speed first. Now, what is it, exactly? Shutter speed is the amount of time the shutter is open and exposes the camera's sensor to light. The longer the shutter is open, the more light that enters the camera.

The size of the aperture (the f-stop number) also determines the amount of diffraction that occurs. A small aperture (large f-stop number) will cause more diffraction, while a large aperture (small f-stop number) will cause less diffraction.

But for many applications, most notably microscopy, there was no escaping the issue. It was not until the 18th century that compound lenses – doublets, a convex and a concave lens of differing refractive indices – began to be used.

As you might expect, the larger the aperture, the more light that enters the camera. This is important because it allows you to control exposure.

Aperture in microscope

Bokeh is a technique in photography that is used to create a soft, blurred background. This effect is achieved by using a large aperture and keeping the subject in focus while the background is out of focus.

If Abbé meant this as a provocation, it worked: he was contacted by a young scientist, Otto Schott. Born into a family of glassmakers, Schott was perfect for the task. He had studied chemistry and mineralogy in Aachen, Würzburg and Leipzig before obtaining his doctorate in Jena in 1875 on the Theory and practice of glassmaking. Schott was now experimenting with glass compositions and sent his samples to Abbé, who was seriously impressed.

Reading this post won’t help you master it, though. The best bet is to grab your photo and start experimenting in the real world!

Aperture photography

If you want to isolate your subject from the background (or foreground), then you'll want to use a large aperture (small f-stop number). This is known as shallow depth of field, and it's often used in portraits and close-up shots.

When I was a kid, my grandfather, a retired executive of the great French glassmaker St Gobain, would occasionally let me use his Zeiss binoculars. ‘Best optics in the world,’ he would say, muttering ‘Schott’ – a mysterious word that meant nothing to me. Only much later, long after his death, did I realise that it was the name of his employer’s European rival, and of the man who solved a 400 year old problem.

Abbé established a theoretical limit for the resolving power of an optical device, and realised that existing instruments came nowhere near it. But the problem was not poor design: a methodical survey of every type of glass on the market revealed that the limitation was the glass itself.

Most DSLR cameras from companies like Nikon and Canon will have a lower f-stop number (or maximum aperture) of f/1.4. This a very wide aperture opening, and will let in a lot of light.

In 1882, with Abbé’s help and funded by the Prussian government, Schott moved to new workshops in Jena – fully equipped with the latest furnaces and burners. He now had the means to carefully melt mixtures of oxides under very controlled conditions, and have them tested by Abbé in labs just up the road. Schott replaced some of the silicate with borate and phosphate, the oxygen with fluoride; then the sodium with potassium and especially with lithium. With the right ratios he could suppress crystallisation and the tendency of the glass to ‘tarnish’ in moist air. Other oxides such as zinc and aluminium were also used to modify the glass. In what might seem an unbearably tedious series of experiments – by 1886 he had conducted over 1000 meltings – he systematically mapped out the composition space of glass.

Within a year of moving to Jena, Schott had a lithium-based glass that could realise Newton’s and Abbé’s dream: the separation of refractive index and dispersion. In the words of a contemporary commentator, the choice of glass was now two-dimensional. Such was the commercial promise of the enterprise that Zeiss, Schott and Abbé agreed to form an equal partnership. Abbé developed a new compound lens with the glass, the apochromat, which performed at the theoretical limit. The new partnership was now the world leader in optics.

Aperture in physics

So as you can see, changing the aperture has an impact on both the depth of field and the shutter speed. It's important to understand how these two factors work together to create the right exposure for your photograph.

In 1876, Abbé gave a lecture in London on lens materials in which he bemoaned the state of European glassmaking. Although glass was being manufactured with unparalled excellence, improvements in optical performance would only be possible if new kinds of glass were invented. And with only two significant producers, Abbé saw little hope that anyone would innovate.

Here's an example to illustrate how this works. Let's say you're taking a picture of a flower garden with a 50mm lens at f/8. The depth of field would be approximately 2 feet (0.6 meters). This means that objects within 2 feet of the camera would appear sharp, while objects beyond that would start to become blurry.

Aperture of lens

This mode is also sometimes called "semi-manual" mode because the photographer still has some control over the exposure. For example, if the scene is very bright, the photographer can choose a small aperture to avoid overexposing the image. Conversely, if the scene is darker, a larger aperture can be used to let in more light. Aperture priority is a popular mode for many types of photography, including portrait, landscape, and still life. It is also a good choice for beginners who are not yet comfortable with manual mode.

In 1893 the firm launched a revolutionary range of borosilicate laboratory glassware, named Duran – the material that has incubated so many of our chemical careers. Then came glass to shield the millions of Auer gas lights that were sprouting on Europe’s streets; Jena glass was synonymous with quality.

That's our post! As you can see aperture is an incredibly important aspect of digital photography. Some of the jargon isn't easy to understand, and probably won't become second-nature until you've had some practice out in the world.

Aperture in biology

Your lens aperture settings will also impact the depth of field in your photograph. What’s more, changing your aperture will impact what you can achieve with your shutter speed and ISO settings.

On a DSLR camera, adjusting the aperture is as simple as turning a dial. This adjusts how wide open the lens is, and therefore how much light is allowed in. As we’ve mentioned already aperture is measured in "f-stops", with larger numbers representing a smaller aperture. For example, an aperture of f/22 would be much smaller than an aperture of f/2.8.

Aperture is one of three camera settings — along with ISO and shutter speed — that impact how well (or not) your photo is exposed. These three settings are often called the ‘exposure triangle.’

As we've explained, changing the aperture can have a big impact on your image. But how do you know which aperture to use? Well, it depends on the look you're going for.

So what is aperture? Here’s a simple definition: Aperture is the size of the opening in your camera lens (the word is literally a fancy way of saying 'opening). This determines how much light enters your camera and hits the image sensor.

Second, exposure isn't only set by your aperture. Your shutter speed and ISO settings also affect exposure, and you'll need to do some trial and error to figure out how to get the exposure you want. That’s why people call these three settings the ‘exposure triangle'.’

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Aperture pronunciation

Depth of field (DOF) is the distance between the nearest and farthest objects in a scene that have crisp details and no unintentional blurring (otherwise known as 'sharp'). It's important to note that depth of field is not an absolute value, but rather it is relative to the distance between the camera and the subject.

Aperture is measured in an f-stop number. The lower the f-stop number, the more open the aperture is and therefore more light enters your camera. The higher the f-stop number, the more closed down (or smaller) the aperture is and less light enters your camera.

The size of the aperture (the f-stop number) also determines the shutter speed that's needed to achieve a correct exposure. A small aperture (large f-stop number) will require a longer shutter speed to achieve the correct exposure, while a large aperture (small f-stop number) will require a shorter shutter speed.

It's important to understand that aperture is not a setting on your camera, but rather a characteristic of your lens. The aperture is determined by the physical size of the diaphragm, which can be changed by swapping out lenses or adjusting a zoom lens.

The f-stop number is calculated by dividing the focal length of the lens by the diameter of the aperture. For example, if a lens has a focal length of 50mm and an aperture diameter of 25mm, the f-stop would be 2 (50/25).

Aperture of mirror

The size of the aperture (the f-stop number) also determines the minimum focus distance of the lens. The minimum focus distance is the closest distance that the lens can focus on an object and still produce a sharp image.

The size of the aperture (the f-stop number) also determines the ISO that's needed to achieve a correct exposure. A small aperture (large f-stop number) will require a lower ISO setting, while a large aperture (small f-stop number) will require a higher ISO setting.

For my grandfather, the name Schott may have meant nemesis. Two generations on, to my ears, it speaks of genius and vision.

It sounds complicated, and some of the terminology ('f-stop', ‘bokeh’) doesn't help! But as with most aspects of photography, it all gets a lot simpler after you start experimenting with different apertures in the real world.

When Galileo first pointed his telescope into the night sky, he not only changed our idea of our place in the universe, but he also opened up a Pandora’s box of optical fascination. For while he famously saw the movement of the moons of Jupiter, and the jagged outlines of mountains on the Moon, everything he saw was tinged with colour. This chromatic aberration results from dispersion: each wavelength of light is refracted differently as it travels through the lens, so they are each focused differently, which distorts the image. For Isaac Newton, the problem was so pernicious that he invented the reflecting telescope as a means of side-stepping the problem altogether.

The size of the camera aperture (the f-stop number) determines the amount of depth of field in an image. A small aperture (large f-stop number) results in a large depth of field, while a large aperture (small f-stop number) results in a shallow depth of field.

Prime lenses are often used for portrait photography, who want to capture clean, sharp images with minimal distortion. Prime lenses are also often used by landscape photographers. While they generally require the use of a tripod or other stabilising device due to their narrow field of view, prime lenses offer a number of advantages that make them a popular choice among professional photographers.

Aperture in camera

For example, let's say you're taking a picture of a person in low light with a 50mm lens at f/2. The lowest ISO setting you could use to get a correct exposure would be 3200. If you wanted to use a lower ISO setting, you would need to use a larger aperture (smaller f-stop number). Conversely, if you wanted to use a higher ISO setting, you would need to use a smaller aperture (larger f-stop number).

That’s right: you can change the amount of light (aperture) and the sensitivity to light (ISO). As you can imagine, changing one of these settings is likely to impact how the other works.

These so-called achromatic lenses were a remarkable improvement. But for microscopists like Carl Zeiss, who traded on optical perfection, they just weren’t good enough. Zeiss turned to Ernst Abbé, an ambitious young physicist who was developing a rigorous theory of optics.

Our advice: read this guide, take your camera off auto mode, and then start taking some photos of your own (maybe for your next photo essay). It might be worth bookmarking this page, taking some photos, and then coming back for another read.

But Schott’s friendship with Abbé had another result. Abbé had progressive ideas about the relationship between a firm and its employees. Both Schott and his son Erich transferred their shares in the company to the Zeiss Foundation that Abbé had founded after Carl Zeiss’s death – a charitable enterprise devoted to furthering teaching and research, and to supporting both workers and the local community. Today Schott and Carl Zeiss are almost unique: huge multinational firms run entirely on a fiduciary basis for the benefit of Zeiss’ ideals.

For example, let's say you're taking a picture of a person with a 50mm lens at f/2. The amount of diffraction would be minimal. If you wanted to use a smaller aperture (larger f-stop number), the amount of diffraction would increase.

Generally speaking, a higher f-stop number will result in a photo with a small area in focus and a large area out of focus. On the flip side, a small f-stop number will result in a photo with a large area in focus and a small area out of focus.

Many professional photographers use a prime lens for this reason. A prime lens is a camera lens with a fixed focal length. In other words, it can't zoom in or out like a zoom lens can.

First, aperture controls the depth of field in your photograph. What is depth of field? It’s the distance between the nearest and furthest objects in a scene that appear ‘sharp’ in an image. The larger the aperture, the shallower the depth of field and the smaller this distance will be. This can be useful for isolating a subject from its background.

If you want everything in your image to be sharp and in focus, then you'll want to use a small aperture (large f-stop number). This is often desirable for landscape shots, group photos, and other situations where you want everything to be sharp.

What about the third part of the exposure triangle, ISO? ISO is a measure of the camera's sensitivity to light. The higher the ISO number, the more sensitive the camera is to light. This means that less light is needed to achieve a correct exposure.

Bokeh can be used to create a dreamy or romantic look, or to make the subject stand out against a busy background. It is also often used in portraiture to help the subject stand out from the background. Bokeh can be created with any type of camera, but it is most commonly associated with DSLRs and mirrorless cameras.

Remember, when adjusting aperture, it's important to keep in mind the shutter speed and ISO settings as well. If you need to increase the shutter speed to prevent blur, you'll need to decrease the aperture to compensate. And if you need to increase the ISO to get a good exposure, you'll need to decrease the aperture as well.

As a result, prime lenses typically have a wider maximum aperture than zoom lenses, making them well-suited for low-light photography and achieving shallow depth of field effects. The wider aperture also allows for greater control over the placement of focus within the frame.

Diffraction is an optical effect that occurs when light waves pass through a small opening. The result is a loss of sharpness in the image.

Aperture is one of the most important concepts in digital photography, yet it is often misunderstood. Here’s the simple definition: Aperture is the size of the opening in the lens through which light passes.

So, we’ve talked about aperture and f-stop. But as we mentioned above, changing your aperture settings will likely require you to make some adjustments to the other settings in the exposure triangle.

Now let's say you take the same picture with the same lens, but at f/2. The depth of field would be reduced to about 0.6 feet (0.2 meters). This means that only objects within 0.6 feet of the camera would appear sharp; anything beyond that would be significantly blurred.

But Schott’s work was not just about optics. In March 1883, he increased the boron content of a batch of glass and found that its tiny thermal expansion made it perfect for thermometers. His borosilicate could also withstand thermal shock as well, if not better, than existing tempered glass without the need for heat treatment. And it seemed almost immune to chemical attack except under the most vicious conditions.