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.

Figure 6 shows the effect of two polarizing filters on originally unpolarized light. The first filter polarizes the light along its axis. When the axes of the first and second filters are aligned (parallel), then all of the polarized light passed by the first filter is also passed by the second. If the second polarizing filter is rotated, only the component of the light parallel to the second filter’s axis is passed. When the axes are perpendicular, no light is passed by the second.

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All we need to solve these problems are the indices of refraction. Air has n1 = 1.00, water has n2 = 1.333, and crown glass has n′2=1.520. The equation [latex]\tan\theta_{\text{b}}=\frac{n_2}{n_1}\\[/latex] can be directly applied to find θb in each case.

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.

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.

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'.’

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.

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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.

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.

17. (a) 2.07 × 10−2 °C/s; (b) Yes, the polarizing filters get hot because they absorb some of the lost energy from the sunlight.

201335 — Unpolarized light is just a collection of polarized photons with not the same polarization so in average, light is not polarized.

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).

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.

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When the intensity is reduced by 90.0%, it is 10.0% or 0.100 times its original value. That is, I = 0.100I0. Using this information, the equation I = I0 cos2 θ can be used to solve for the needed angle.

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Polarizing filters have a polarization axis that acts as a slit. This slit passes electromagnetic waves (often visible light) that have an electric field parallel to the axis. This is accomplished with long molecules aligned perpendicular to the axis as shown in Figure 9.

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Figure 9. Long molecules are aligned perpendicular to the axis of a polarizing filter. The component of the electric field in an EM wave perpendicular to these molecules passes through the filter, while the component parallel to the molecules is absorbed.

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.

Figure 4. The slender arrow represents a ray of unpolarized light. The bold arrows represent the direction of polarization of the individual waves composing the ray. Since the light is unpolarized, the arrows point in all directions.

Figure 3. The transverse oscillations in one rope are in a vertical plane, and those in the other rope are in a horizontal plane. The first is said to be vertically polarized, and the other is said to be horizontally polarized. Vertical slits pass vertically polarized waves and block horizontally polarized waves.

Brewster’s law: [latex]\tan\theta_{\text{b}}=\frac{{n}_{2}}{{n}_{1}}\\[/latex], where n1 is the medium in which the incident and reflected light travel and n2 is the index of refraction of the medium that forms the interface that reflects the light

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What angle is needed between the direction of polarized light and the axis of a polarizing filter to reduce its intensity by 90.0%?

In flat screen LCD televisions, there is a large light at the back of the TV. The light travels to the front screen through millions of tiny units called pixels (picture elements). One of these is shown in Figure 12 (a) and (b). Each unit has three cells, with red, blue, or green filters, each controlled independently. When the voltage across a liquid crystal is switched off, the liquid crystal passes the light through the particular filter. One can vary the picture contrast by varying the strength of the voltage applied to the liquid crystal.

Figure 13. Optical activity is the ability of some substances to rotate the plane of polarization of light passing through them. The rotation is detected with a polarizing filter or analyzer.

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.’

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.

Light is one type of electromagnetic (EM) wave. As noted earlier, EM waves are transverse waves consisting of varying electric and magnetic fields that oscillate perpendicular to the direction of propagation (see Figure 2). There are specific directions for the oscillations of the electric and magnetic fields. Polarization is the attribute that a wave’s oscillations have a definite direction relative to the direction of propagation of the wave. (This is not the same type of polarization as that discussed for the separation of charges.) Waves having such a direction are said to be polarized. For an EM wave, we define the direction of polarization to be the direction parallel to the electric field. Thus we can think of the electric field arrows as showing the direction of polarization, as in Figure 2.

Figure 6. The effect of rotating two polarizing filters, where the first polarizes the light. (a) All of the polarized light is passed by the second polarizing filter, because its axis is parallel to the first. (b) As the second is rotated, only part of the light is passed. (c) When the second is perpendicular to the first, no light is passed. (d) In this photograph, a polarizing filter is placed above two others. Its axis is perpendicular to the filter on the right (dark area) and parallel to the filter on the left (lighter area). (credit: P.P. Urone)

Figure 8 illustrates what happens when unpolarized light is reflected from a surface. Vertically polarized light is preferentially refracted at the surface, so that the reflected light is left more horizontally polarized. The reasons for this phenomenon are beyond the scope of this text, but a convenient mnemonic for remembering this is to imagine the polarization direction to be like an arrow. Vertical polarization would be like an arrow perpendicular to the surface and would be more likely to stick and not be reflected. Horizontal polarization is like an arrow bouncing on its side and would be more likely to be reflected. Sunglasses with vertical axes would then block more reflected light than unpolarized light from other sources.

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While you are undoubtedly aware of liquid crystal displays (LCDs) found in watches, calculators, computer screens, cellphones, flat screen televisions, and other myriad places, you may not be aware that they are based on polarization. Liquid crystals are so named because their molecules can be aligned even though they are in a liquid. Liquid crystals have the property that they can rotate the polarization of light passing through them by 90º. Furthermore, this property can be turned off by the application of a voltage, as illustrated in Figure 12. It is possible to manipulate this characteristic quickly and in small well-defined regions to create the contrast patterns we see in so many LCD devices.

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).

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.

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Find Polaroid sunglasses and rotate one while holding the other still and look at different surfaces and objects. Explain your observations. What is the difference in angle from when you see a maximum intensity to when you see a minimum intensity? Find a reflective glass surface and do the same. At what angle does the glass need to be oriented to give minimum glare?

Many crystals and solutions rotate the plane of polarization of light passing through them. Such substances are said to be optically active. Examples include sugar water, insulin, and collagen (see Figure 13). In addition to depending on the type of substance, the amount and direction of rotation depends on a number of factors. Among these is the concentration of the substance, the distance the light travels through it, and the wavelength of light. Optical activity is due to the asymmetric shape of molecules in the substance, such as being helical. Measurements of the rotation of polarized light passing through substances can thus be used to measure concentrations, a standard technique for sugars. It can also give information on the shapes of molecules, such as proteins, and factors that affect their shapes, such as temperature and pH.

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.

Polaroid sunglasses are familiar to most of us. They have a special ability to cut the glare of light reflected from water or glass (see Figure 1). Polaroids have this ability because of a wave characteristic of light called polarization. What is polarization? How is it produced? What are some of its uses? The answers to these questions are related to the wave character of light.

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.

Figure 5. A polarizing filter has a polarization axis that acts as a slit passing through electric fields parallel to its direction. The direction of polarization of an EM wave is defined to be the direction of its electric field.

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.

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.

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.

There is a range of optical effects used in sunglasses. Besides being Polaroid, other sunglasses have colored pigments embedded in them, while others use non-reflective or even reflective coatings. A recent development is photochromic lenses, which darken in the sunlight and become clear indoors. Photochromic lenses are embedded with organic microcrystalline molecules that change their properties when exposed to UV in sunlight, but become clear in artificial lighting with no UV.

[latex]\tan\theta_{\text{b}}=\frac{n_2}{n_1}\\[/latex] gives [latex]\tan\theta_{\text{b}}=\frac{n_2}{n_1}=\frac{1.333}{1.00}=1.333\\[/latex].

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.

Figure 8. Polarization by reflection. Unpolarized light has equal amounts of vertical and horizontal polarization. After interaction with a surface, the vertical components are preferentially absorbed or refracted, leaving the reflected light more horizontally polarized. This is akin to arrows striking on their sides bouncing off, whereas arrows striking on their tips go into the surface.

Brewster’s angle: [latex]{\theta }_{\text{b}}={\tan}^{-1}\left(\frac{{n}_{2}}{{n}_{1}}\right)\\[/latex], where n2 is the index of refraction of the medium from which the light is reflected and n1 is the index of refraction of the medium in which the reflected light travels

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.

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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.

Reflection implies the rebounding of light, sound, heat, or another object back to the source, without absorbing it.

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.

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A fairly large angle between the direction of polarization and the filter axis is needed to reduce the intensity to 10.0% of its original value. This seems reasonable based on experimenting with polarizing films. It is interesting that, at an angle of 45º, the intensity is reduced to 50% of its original value (as you will show in this section’s Problems & Exercises). Note that 71.6º is 18.4º from reducing the intensity to zero, and that at an angle of 18.4º the intensity is reduced to 90.0% of its original value (as you will also show in Problems & Exercises), giving evidence of symmetry.

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.

To examine this further, consider the transverse waves in the ropes shown in Figure 3. The oscillations in one rope are in a vertical plane and are said to be vertically polarized. Those in the other rope are in a horizontal plane and are horizontally polarized. If a vertical slit is placed on the first rope, the waves pass through. However, a vertical slit blocks the horizontally polarized waves. For EM waves, the direction of the electric field is analogous to the disturbances on the ropes.

Figure 12. (a) Polarized light is rotated 90º by a liquid crystal and then passed by a polarizing filter that has its axis perpendicular to the original polarization direction. (b) When a voltage is applied to the liquid crystal, the polarized light is not rotated and is blocked by the filter, making the region dark in comparison with its surroundings. (c) LCDs can be made color specific, small, and fast enough to use in laptop computers and TVs. (credit: Jon Sullivan)

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.

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.

This phenomenon, known as Aberration of Light, offers a glimpse into the fundamental nature of light and the Earth's journey around the Sun.

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.

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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.

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!

Photographs of the sky can be darkened by polarizing filters, a trick used by many photographers to make clouds brighter by contrast. Scattering from other particles, such as smoke or dust, can also polarize light. Detecting polarization in scattered EM waves can be a useful analytical tool in determining the scattering source.

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.

Another interesting phenomenon associated with polarized light is the ability of some crystals to split an unpolarized beam of light into two. Such crystals are said to be birefringent (see Figure 15). Each of the separated rays has a specific polarization. One behaves normally and is called the ordinary ray, whereas the other does not obey Snell’s law and is called the extraordinary ray. Birefringent crystals can be used to produce polarized beams from unpolarized light. Some birefringent materials preferentially absorb one of the polarizations. These materials are called dichroic and can produce polarization by this preferential absorption. This is fundamentally how polarizing filters and other polarizers work. The interested reader is invited to further pursue the numerous properties of materials related to polarization.

The Sun and many other light sources produce waves that are randomly polarized (see Figure 4). Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization. Polaroid materials, invented by the founder of Polaroid Corporation, Edwin Land, act as a polarizing slit for light, allowing only polarization in one direction to pass through. Polarizing filters are composed of long molecules aligned in one direction. Thinking of the molecules as many slits, analogous to those for the oscillating ropes, we can understand why only light with a specific polarization can get through. The axis of a polarizing filter is the direction along which the filter passes the electric field of an EM wave (see Figure 5).

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.

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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.

Figure 7. A polarizing filter transmits only the component of the wave parallel to its axis, , reducing the intensity of any light not polarized parallel to its axis.

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.

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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.

Since the part of the light that is not reflected is refracted, the amount of polarization depends on the indices of refraction of the media involved. It can be shown that reflected light is completely polarized at a angle of reflection θb, given by [latex]\tan\theta_{\text{b}}=\frac{n_2}{n_1}\\[/latex], where n1 is the medium in which the incident and reflected light travel and n2 is the index of refraction of the medium that forms the interface that reflects the light. This equation is known as Brewster’s law, and θb is known as Brewster’s angle, named after the 19th-century Scottish physicist who discovered them.

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.

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Figure 14. Optical stress analysis of a plastic lens placed between crossed polarizers. (credit: Infopro, Wikimedia Commons)

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.

Figure 11. Polarization by scattering. Unpolarized light scattering from air molecules shakes their electrons perpendicular to the direction of the original ray. The scattered light therefore has a polarization perpendicular to the original direction and none parallel to the original direction.

polarization: the attribute that wave oscillations have a definite direction relative to the direction of propagation of the wave

If you hold your Polaroid sunglasses in front of you and rotate them while looking at blue sky, you will see the sky get bright and dim. This is a clear indication that light scattered by air is partially polarized. Figure 11 helps illustrate how this happens. Since light is a transverse EM wave, it vibrates the electrons of air molecules perpendicular to the direction it is traveling. The electrons then radiate like small antennae. Since they are oscillating perpendicular to the direction of the light ray, they produce EM radiation that is polarized perpendicular to the direction of the ray. When viewing the light along a line perpendicular to the original ray, as in Figure 11, there can be no polarization in the scattered light parallel to the original ray, because that would require the original ray to be a longitudinal wave. Along other directions, a component of the other polarization can be projected along the line of sight, and the scattered light will only be partially polarized. Furthermore, multiple scattering can bring light to your eyes from other directions and can contain different polarizations.

Only the component of the EM wave parallel to the axis of a filter is passed. Let us call the angle between the direction of polarization and the axis of a filter θ. If the electric field has an amplitude E, then the transmitted part of the wave has an amplitude E cos θ (see Figure 7). Since the intensity of a wave is proportional to its amplitude squared, the intensity I of the transmitted wave is related to the incident wave by I = I0 cos2 θ, where I0 is the intensity of the polarized wave before passing through the filter. (The above equation is known as Malus’s law.)

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.

Figure 15. Birefringent materials, such as the common mineral calcite, split unpolarized beams of light into two. The ordinary ray behaves as expected, but the extraordinary ray does not obey Snell’s law.

By now you can probably guess that Polaroid sunglasses cut the glare in reflected light because that light is polarized. You can check this for yourself by holding Polaroid sunglasses in front of you and rotating them while looking at light reflected from water or glass. As you rotate the sunglasses, you will notice the light gets bright and dim, but not completely black. This implies the reflected light is partially polarized and cannot be completely blocked by a polarizing filter.

Figure 2. An EM wave, such as light, is a transverse wave. The electric and magnetic fields are perpendicular to the direction of propagation.

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.

Light reflected at these angles could be completely blocked by a good polarizing filter held with its axis vertical. Brewster’s angle for water and air are similar to those for glass and air, so that sunglasses are equally effective for light reflected from either water or glass under similar circumstances. Light not reflected is refracted into these media. So at an incident angle equal to Brewster’s angle, the refracted light will be slightly polarized vertically. It will not be completely polarized vertically, because only a small fraction of the incident light is reflected, and so a significant amount of horizontally polarized light is refracted.

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.

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.

Figure 1. These two photographs of a river show the effect of a polarizing filter in reducing glare in light reflected from the surface of water. Part (b) of this Figure was taken with a polarizing filter and part (a) was not. As a result, the reflection of clouds and sky observed in part (a) is not observed in part (b). Polarizing sunglasses are particularly useful on snow and water. (credit: Amithshs, Wikimedia Commons)

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.

Figure 10. Artist’s conception of an electron in a long molecule oscillating parallel to the molecule. The oscillation of the electron absorbs energy and reduces the intensity of the component of the EM wave that is parallel to the molecule.

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.

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.

Figure 10 illustrates how the component of the electric field parallel to the long molecules is absorbed. An electromagnetic wave is composed of oscillating electric and magnetic fields. The electric field is strong compared with the magnetic field and is more effective in exerting force on charges in the molecules. The most affected charged particles are the electrons in the molecules, since electron masses are small. If the electron is forced to oscillate, it can absorb energy from the EM wave. This reduces the fields in the wave and, hence, reduces its intensity. In long molecules, electrons can more easily oscillate parallel to the molecule than in the perpendicular direction. The electrons are bound to the molecule and are more restricted in their movement perpendicular to the molecule. Thus, the electrons can absorb EM waves that have a component of their electric field parallel to the molecule. The electrons are much less responsive to electric fields perpendicular to the molecule and will allow those fields to pass. Thus the axis of the polarizing filter is perpendicular to the length of the molecule.

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.

Glass and plastic become optically active when stressed; the greater the stress, the greater the effect. Optical stress analysis on complicated shapes can be performed by making plastic models of them and observing them through crossed filters, as seen in Figure 14. It is apparent that the effect depends on wavelength as well as stress. The wavelength dependence is sometimes also used for artistic purposes.