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 (Figure \(\PageIndex{5}\)).

Circularpolarization

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.

First affordable compact Nikkor zoom to utilize an aspherical element within. The AF Zoom Nikkor 28-70 f3.5/4.5 D, definitely will not be the last from Nikon.

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 berefringent (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.

Fast lenses, at times has problem maintaining its optical performance at widest opening, especially in situation where the illumination is dim. A aspherical lens can assure optimum correction of coma. Like images of scenes with small points of light - bright point sources of light near the edges of the picture appear as dots rather than comet-shaped blurs. Some newer generation of fast lens, like the world's fastest 28mm lens, the AF Nikkor 28mm f/1.4D, or the recent Canon's super fast EF 50mm f1.0 L use an aspherical element to ensure compact size and to obtain superb performance by eliminating sagittal, or arrow shaped, coma, even at its widest aperture.

Sometimes, these advertisements can make public look suspiciously at their current lenses in the camera bag and generate a uneasy feeling of owning some inferior quality lenses which are without an aspherical lens elements.

The OP-Fisheye Nikkor 10mm f5.6 is one of the earliest in Nikkor family to use an aspherical lens front element to ensure its mathematically correct illumination pattern.

where \(I_{0}\) is the intensity of the polarized wave before passing through the filter. Equation \ref{27.9.1} is known as Malus’s law.

Though early days, the concept of adoptions of aspherical design were to certain specialized lenses where its benefits can be fully realized in specific applications. But since with the wide acceptance and popularity of zoom lenses by many serious SLR users nowadays, you will be rest assured that new generation of aspherical zoom and prime lenses will be coming in with more "varieties" and economically - in a grand scale. The solid AF Nikkor 28mm f1.4D is not cheap, one of the first few new generation of AF- Nikkor from Nikon came with an aspherical lens element.

Polarisation meaning in Physics

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 (Figure \(\PageIndex{2}\)). 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 \(\PageIndex{2}\).

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.

To examine this further, consider the transverse waves in the ropes shown in Figure \(\PageIndex{3}\). 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.

When the intensity is reduced by \(90.0 \%\), it is \(10.0 \%\) or 0.100 times its original value. That is, \(I = 0.100 I_{0}\). Using this information, the equation \(I = I_{0}\cos{\theta}^{2}\) can be used to solve for the needed angle.

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 \(90^{\circ}\). Furthermore, this property can be turned off by the application of a voltage, as illustrated in Figure \(\PageIndex{12}\). 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.

This page titled 27.8: Polarization is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by OpenStax via source content that was edited to the style and standards of the LibreTexts platform.

Aspherical lenses incorporating some optical characteristics. These lenses are small, lighter and in general, better than similar lenses which only employ spherical elements. In some instances, using an aspherical element enable the lens designer to use fewer lens elements. The benefit can be a smaller, compact and lighter lens; with fewer lens surfaces, there is also less potential for internal reflection - that is why there are more and more zoom lenses incorporating a (or few) aspherical lens element within to substitute a number (Depends on optical design).

Tamron's Aspherical lens 28-200mm f3.8/5.6 LD IF is only 3.2" in length. First started the 28-200 compact zoom revolution in 1992, current version packs all modern features like low dispersion glass, internal focus and aspherical lens surface. Another 3.2" compact offer from Tamron, the SP AF20-40mm F/2.7-3.5 Aspherical (IF). Packing features like dual aspherical elements: Large diameter Hybrid Aspherical elements are used in the front focus group to substantially compensate for distortion aberrations at wide angle. Another Hybrid Aspherical element added to the rear group effectively eliminates comatic flare.

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?

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 \(\theta_{b}\), given by \[\tan{\theta_{b}} = \frac{n_{2}}{n_{1}}, \label{27.9.4}\] where \(n_{1}\) is the medium in which the incident and reflected light travel and \(n_{2}\) 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 \(\theta_{b}\) is known as Brewster's angle, named after the 19th-century Scottish physicist who discovered them.

Linearpolarization

Current manufacturing precision standard which can have a tight tolerance of asphericity to be within 0.1 micron and thus popularizing the broad usage of aspherical lens elements for optical designers. Anyway, the topic has become a selling point for many optical lens producers, those marketing guys might do whatever it takes to sell you the idea of substituting your current lenses in your camera bag now. And there is a strong possibility that most new higher grade zooms will have a element or few within in time to come (because once the floodgate is opened, the rest without a aspherical element won't be selling well). And we will benefit from it.

Among the top five camera manufacturers in Japan, Canon is the most aggressive among the few to push the technology into their EF-L series lenses. Although many may not realize, the world's first SLR lens to have an aspherical element incorporated within was a FD 55mm f1.2 AL SSC.

Polaroid sunglasses are familiar to most of us. They have a special ability to cut the glare of light reflected from water or glass (Figure \(\PageIndex{1}\)). 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.

Lately, I am disturbed by some marketing kit which carries a lot of advertisement that talk about lenses with Aspherical lens elements. These manufacturers are pushing hard and aggressively promoting a new breed of lenses that carries with a tag called Aspherical Lens..

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.

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.

To a manufacturer, it means it can be cheaper to produce a lens, besides, while along the way, optical performance can be improved as well (Theoretically). Basically, they are thinking of ways to be more competitive on the market place and after the investment in the manufacturing processes of producing aspherical lens elements, naturally, this becomes a marketing tool to boost the sales and get the fastest return on investment. Simplest way to illustrate what a aspherical lens element is all about. Technically, an aspherical lens is a lens whose curved surface does not conform to the shape of a sphere; lenses are usually ground or molded with spherical surfaces; because a spherical surface lens has difficulty in correcting distortion in ultra-wideangle lenses or coma in large-aperture lenses brought about by spherical aberration, an aspherical lens is used. Where in the case of zoom lenses, a lens element or two can substitute a bigger number of lens elements to achieve similar or better optical results and to reduce the overall cost of production and more compact of the size of a lens - especially in the case of zoom lenses, where lens elements of more than 10 are not too unusual.

Sometimes, the light passing through the central area of a lens cannot be focused at precisely the same plane as the light passing through the peripheral areas. This is a spherical aberration that makes sharpness inconsistent. While this phenomenon is not always a problem, some lens designs can be significantly improved to higher levels of overall sharpness through the use of aspherical elements.

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.

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 (Figure \(\PageIndex{13}\)). 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.

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 \(\PageIndex{12a}\) and \(\PageIndex{12b}\). 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.

Generally, for the vast majority of even the most demanding applications, conventional lenses are much more than adequate. Where previously, due to the high cost and tedious production process of producing aspherical lens elements, most manufacturers who has the technology to produce these elements only restrict the use of aspherical surfaces to lenses where they are essential.

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.

Direction of polarization ofelectromagnetic waves

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.

Direction of polarizationformula

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 \(\theta\). If the electric field has an amplitude \(E\), then the transmitted part of the wave has an amplitude \(E \cos{\theta}\) (Figure \(\PageIndex{7}\)). 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

Planeof polarization

All we need to solve these problems are the indices of refraction. Air has \(n_{1} = 100\), water has \(n_{2} = 1.333\), and crown glass has \(n'_{2} = 1.520\). The equation \(\tan{\theta_{b}} = \frac{n_{2}}{n_{1}}\) can be directly applied to find \(\theta_{b}\) in each case.

Direction of polarizationpdf

Recent development of seeing more and more exciting lenses made possible after individual manufacturer found various solutions in manufacturing process to produce aspherical lens elements. Tamron developed a method of apply and treating an optical resin to normal spherical surface of a lens to made it aspherical; Nikon overcame its problem in grinding etc..all these accounted for the sudden emergence of lenses of all types with a or a few aspherical lens elements within.

Solving the equation \(I = I_{0} \cos{\theta}^{2}\) for \(\cos{\theta}\) and substituting with the relationship between \(I\) and \(I_{0}\) gives

Think of rushing out to get one or replacing your current lenses ? No necessity We have forgotten those older SLR lenses that were out there since the late '50 have produced millions of faithful, good and stunning images that has impressed all of us and there is absolutely no hurry to change unless you have lost, spoilt or damaged yours and looking for a fresh replacement. Well, it is just a fruitful product along with the natural course in the lens development and technology.

The Sun and many other light sources produce waves that are randomly polarized (Figure \(\PageIndex{4}\)). Such light is said to be unpolarized because it is composed of many waves with all possible directions of polarization.

Similarly, for crown glass and air, \[\tan{\theta_{b}'} = \frac{n'_{2}}{n_{1}} = \frac{1.520}{1.00} = 1.52.\] Thus, \[\theta_{b}' = \tan{1.52}^{-1} = 56.7^{\circ}.\]

Anyway, the existence of aspherical lens has been quite a while on the market. Like the time honored Noct-Nikkor 58mm f1.2 and the discontinued OP-Fisheye Nikkor 10mm f5.6 from Nikon has been around for almost two decades are just two classical examples. Each representing lenses for some specific applications, like general or scientific/Industrial use.

Simplest way to illustrate what a aspherical lens element is all Spherical aberration of a spherical lens and convergence of parallel light rays with the use of a aspherical lens element.about.

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.

Direction of polarizationin physics

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 \(\PageIndex{11}\) 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.

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Figure \(\PageIndex{6}\) 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.

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

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 \(45^{\circ}\), the intensity is reduced to \(50\%\) of its original value (as you will show in this section’s Problems & Exercises). Note that \(71.6^{\circ}\) is \(18.4^{\circ}\) from reducing the intensity to zero, and that at an angle of \(18.4^{\circ}\) the intensity is reduced to \(90.0\%\) of its original value (as you will also show in Problems & Exercises), giving evidence of symmetry.

Some bought the idea and disposed off theirs and rushed for an upgrade even that came at similar focal length and lens type. This prompt me to find out some basic resources relates to this and compiled here for everybody to consume and see if it benefits and calm you down a little.