Some of these are strictly cosmetic, but depending on your vision needs, others may “potentially improve your comfort and safety,” says Andrew Iwach, MD, clinical spokesperson for the American Academy of Ophthalmology (AAO).

Dec 20, 2021 — The technical explanation for adjusting aperture settings is fairly simple: the wider the aperture, the narrower your depth of field becomes.

The two forms of circular polarization of light (left or right) are mirror images of each other. First, let’s see what a circularly polarized light wave looks like. We consider only the electric field component of the electromagnetic wave. Suppose you superimpose (add) two linearly polarized electromagnetic waves with the same amplitude and frequency (wavelength) but where the electric field vector in the one case oscillates, say, in the xz plane and in the other case it oscillates in the yz plane. Suppose the waves propagate in the z direction. If the two waves have a phase shift of exactly one quarter of the wavelength, voila! We obtain a light wave where the resulting electric field vector at any point along the z direction turns around on a circle either clock-wise or anti-clock-wise. This is why we call this light wave circularly polarized. See the animation below on the left. In the case that the two amplitudes are not exactly equal, the electric field vector rotates clock-wise or anti-clock-wise on an ellipse instead and we obtain elliptically polarized light. See the animation below on the right. You can also download interactive versions of these animations by following the Download links. You need the Wolfram Player (free download from the Wolfram research web site)

Because the elliptic polarization results from the different absorption coefficients at that wavelength (or frequency), the amount of ellipticity is directly related to the circular dichroism. The difference is that the CD is obtained by considering the absorption of left and right circularly polarized light individually and then taking the difference. Ellipticity can be understood as being the result of doing the experiment with both light polarizations simultaneously (by starting out with linearly polarized light).

What you’ll pay: It’s usually included, especially with sunglasses. Otherwise, an upgrade to 100 percent UV protection may be available. At EyeBuyDirect, for instance, it’s included with an upgrade to thinner lenses. And note that polycarbonate lenses, which are natural UV blockers, offer 100 percent protection, as do many high-index lenses, Vitale says.

Circular polarization

This coating will make your glasses less vulnerable to scratching if you happen to drop them or clean them with an abrasive cloth. “Many glasses wouldn’t last a day without this,” Vitale says. “Polycarbonate and high-index lenses are very soft.”

Buy Tiffany & Co. Tiffany Infinity Tf 2160b Eyeglasses online, see more Tiffany Infinity Tf 2160b Eyeglasses collection with colors and sizes, ...

What to know: The AAO recommends getting 100 percent protection from UVA and UVB rays. Lenses that offer this should be labeled 100 percent UV protection or UV400.

Sep 19, 2022 — The standard magnification level of the ocular lens is 10x, but there are stronger ones available. When selecting an eyepiece, you should think ...

What you’ll pay: Tints cost an average of $74.67, according to the Vision Council’s VisionWatch market research for December 2019. Blue blocking costs $50 at Warby Parker and starts at $19 at EyeBuyDirect.

The graphics below shows an animation of a linear polarized light wave as it passes through an optically active medium (indicated by the rectangular box). The plane of polarization of the light wave rotates proportional to the path length. The box dimension, the amount of rotation, and the amplitudes are not to scale. Optical rotation is measured by polarimetry. The wavelength used in polarimetry experiments is often 589.3 nm (this is the yellow light from a sodium lamp). Optical rotation data are typically given in terms of a path length of 10 cm (1/3 foot).

Be even more cautious about anything that feels high-pressure if you’re in an eyeglass store, he says. If you feel pressured, Vitale says, “you may want to look elsewhere.”

These two forms of circularly polarized light interact slightly differently with a chiral molecule, which causes the circular dichroism. A different interaction of the two forms of circularly polarized light with an enantiomer of a chiral molecule also causes the optical rotation, which is explained further below.

R Smith · 1991 · 1 — Laser beam clipping: two aspects and a safety device. Br J Ophthalmol. 1991 Jul;75(7):385. doi: 10.1136/bjo.75.7.385. Author. R Smith. PMID: 1854688; PMCID ...

Suppose we investigate optical rotation at a wavelength where the medium absorbs some of the light’s intensity. Because a chiral medium absorbs left and right circularly polarized light differently (the CD effect), the amplitudes of the outgoing two circularly polarized components of the light beam are not equal anymore after they have passed through the absorbing chiral medium. They have a phase shift and a different amplitude. We end up with a situation similar to the one depicted in the animation above of elliptic polarization (caused by the different amplitudes of the linearly polarized components). In other words, the outgoing light beam is not linearly polarized anymore. Instead, it is elliptically polarized. See the animation below. It was created with Mathematica in the same way as the animation at the top of the page, but with one of the circular components being reduced in amplitude as it passes through the optically active medium. The ellipticity of the outgoing light is clearly visible in the electric field vector (orange) at some fixed position.

As an example, consider the molecule ‘hexahelicene’. Its chemical formula is shown below on the left (‘hexa’ because of the 6 aromatic rings). The molecule adopts a helical shape as shown in the middle, otherwise the atoms at the ends of the molecule would get too close. There are two possible forms: a left-handed helical form as shown below (M for the ‘Minus’ sense of hecility), and its the mirror image which has a right-handed helical shape (not shown. This molecule is named (P)-hexahelicene, ‘Plus’). Because of its helical shape, the molecule is chiral. It has a very intense CD spectrum shown below on the right. In green is the experiment. The red spectrum is the result of a computation that we performed in 2002 (Ref. [9]) which agrees quite well with the experiment except at the shortest wavelengths where we cut off the computation of additional excitations. (P)-Hexahelicene would have a CD spectrum of the opposite sign.

The plane of polarization of the resulting linearly polarized wave thus prepared can be changed (rotated) by applying a phase shift between its two circularly polarized components. With the help of this concept we can explain the phenomenon of optical rotation: We have seen that chiral molecules interact slightly differently with the two circularly polarized components of a linearly polarized light beam. This is true both for absorption and refraction. Left and right circularly polarized light beams also have slightly different refractive indices in a chiral medium. This means that left and right circularly polarized light travel waves at slightly different speeds through the medium. Therefore, this causes a phase shift between the two circularly polarized components, which increases proportionally to the path length that the light travels through the chiral medium. This phase shift manifests itself as a rotation of the plane of polarization of the resultant linearly polarized light beam—optical rotation. In fact this is exactly how the animation of optical rotation at the top of the page was created with the Mathematica software.

What to know: “Everything on the market now except your most basic standard plastic CR-39 lens [which still made up about 36 percent of the prescription lenses sold in the U.S. in 2019, according to the Vision Council] is probably going to come with scratch-resistant coating already on it,” Vitale says. “And that’s because CR-39 is already pretty scratch-resistant.” To further help keep lenses scratch-free, store your glasses in a case when you’re not wearing them and use a microfiber nonscratch cloth to clean them.

What to know: Tinted lenses are often touted as “curing” color blindness, Brodie says. The truth: A tint may make some color contrasts more visible to people with partial color impairment but may make other contrasts harder to see, so it’s a trade-off.

Circularly polarized light

Any helical object like this one has a mirror image that is also helical but with the opposite sense of rotation. The mirror image and the original are not identical. In a sense, every chiral molecule also has such a helicity built into it.

Interestingly, a monochromatic linearly polarized light beam can be considered as a superposition of two circularly polarized electromagnetic waves that are propagating in the same direction with the same frequency but the opposite sense of rotation. Consider the animation of circularly polarized light above. If we superimpose this wave with a circularly polarized wave of the opposite ‘handedness’ where the blue component is 1/4 wavelength behind (instead of ahead), the two blue components will completely cancel because they are 180 degrees (half a wavelength) out of phase. Thus, we would be left with just a linearly polarized wave.

No matter what your warranty says, if a coating starts to degrade within a year, Vitale recommends taking the glasses back to see whether you can get the problem fixed or the glasses replaced.

Iris Diaphragm controls the amount of light reaching the specimen. It is located above the condenser and below the stage. Most high quality microscopes include ...

In both animations the electric field vector (orange) at a fixed position z in space (here at 12 π) is shown in addition to the wave itself as it propagates. The circular and elliptic polarizations are clearly visible. In blue and red we have the two individual linearly polarized light beams and in green their superposition. Because the ‘green wave’ has the shape of a helix it can be considered chiral in some sense, because there is a left-handed and a right-handed helix which are mirror images of each other. In the animations above, the blue wave is one quarter of a wavelength ahead of the red one. If it were behind instead, we would obtain circularly or elliptically polarized light with the opposite helicity.

As for blue blockers, “there’s probably no harm, though anything that limits the light reaching you can lessen your vision,” Iwach says. “But the benefits have not been proven.” He has also recently seen an increase in interest in yellow-tinted lenses for night driving but cautions that these “can actually complicate things, since in low-light conditions, you want to get the most light in that you can.”

S-polarization vs p-polarization

Prior's motorized linear XY stages, or translation stages, ensure high-precision positioning. We offer a choice of robust and reliable stepper motors and ...

Chiral molecules are molecules that do not have a plane of symmetry, an inversion center, or so-called improper rotation symmetry axes. For example, the water molecule has a plane of symmetry but sugar molecules don’t. See this page for an illustration of various types of molecular chirality. As a consequence, chiral molecules such as sugars, amino acids, and most other bio-molecules, come in two forms (enantiomers) that are mirror images of each other and that are not the same. The concept of chirality is not restricted to molecules; one can also speak of chiral objects in general terms. The term ‘chiral’ means ‘handedness’ and refers to the fact that our hands are mirror images of each other [when you press a hand flat against a mirror it looks the same as if you press your hands flat together] but a hand and its mirror image are not identical and you cannot superimpose them. Chiral objects always come in pairs, conceptually. Back to molecules: Two enantiomers have the same chemical reactivity, the same mass, volume, and so on. One can distinguish them most easily in two ways: First, enantiomers react differently with other chiral molecules. Second, chiral molecules are said to be optically active.

We don’t recognize that sign in. Your username maybe be your email address. Passwords are 6-20 characters with at least one number and letter.

Linearlypolarized electromagnetic wave

Lenses tinted yellow are sometimes marketed as “blue blockers” for their supposed ability to reduce exposure to the light emitted by electronics such as smartphones. The theory is that this may ease both eyestrain and any sleep problems associated with using the devices too close to bedtime.

Typically applied on both sides of an eyeglass lens, this coating, also known as AR or anti-glare, “reduces the amount of light reflected off the surfaces of spectacle lenses, and may enhance the contrast of certain scenes,” says Scott E. Brodie, MD, PhD, professor of ophthalmology at NYU Langone Health in New York City. This means you’re getting the maximum light from the environment you’re in, but without any visual interference that can occur from that light bouncing off your lenses. (The term “anti-glare” is a misnomer, however, says Brodie, and glare—think oncoming headlights—is better addressed with polarized lenses than with AR.)

Linearly polarisedlight

What you’ll pay: Usually included in the price of glasses, but more robust scratch resistance may be built in to some upgraded lens packages.

Feb 28, 2024 — Well-known member ... CA is caused by glass not having a constant refraction index as a function of wavelength, which means different colors are ...

Scan the warranty. Many glasses will be backed up by some kind of warranty, but it might not cover coatings. Or warranties may vary in terms of which ones are covered and for how long. What can you expect? “Virtually all coatings today are designed to last the life of the prescription,” says Vitale, which, on average, is about 28 to 30 months.

Put price in perspective. Some types of coating, like those that are anti-reflective (sometimes called glare-reducing), come in a range of prices. But experts say the most expensive option offered isn’t necessarily of significantly higher quality. “I know some ‘house brands’ out there that are pretty similar to the premium versions,” says master optician Michael Vitale, vice president of membership and technical affairs at The Vision Council.

Linearly polarisedmeaning

The types of lenses you choose can make a big difference in the quality of your eyeglasses. Depending on what your eye doctor advises, some people can get along just fine with basic plastic CR-39 lenses, while some may want to consider thinner and pricier polycarbonate or high-index types, which may be more appropriate for stronger prescriptions.

The Blackfly® S leverages the industry's most advanced sensors in an ice-cube form factor. It is packed with powerful features enabling you to easily produce ...

Over time, exposure to the sun’s ultraviolet rays can lead to vision problems such as cataracts and retinal damage. But many eyeglass lenses have a substantial amount of UV protection built in. You can also sometimes buy an additional treatment to safeguard your eyes fully or opt for lenses with 100 percent protection.

The fact that the absorption spectra of a chiral substance measured with left and right circularly polarized light differ somewhat can be rationalized by the fact that circularly polarized light is ‘chiral’ in itself. Why is that? Helical objects are chiral. Look at the pictures below (in case you are curious, this is a bike stand; I forgot where I took the photo):

Think about how you use eyeglasses. Indoors and outdoors? For sports or only for reading or desk work? Driving day and night? Your lifestyle and habits should inform your coating decisions.

How do you know what’s right for you? Your eye doctor may have some suggestions. “These are, by and large, personal decisions,” Iwach says. “One size doesn’t fit all.”

But once you’ve picked frames and lenses, there’s a wide variety of lens coatings to consider, each with its own properties—from light reduction to scratch resistance.

Linearlypolarized wave

Who might consider: Most people, but AR coating may be especially useful for those who often drive at night (it can reduce reflections from headlights at night) and read on computers. It’s strongly recommended with polycarbonate or high-index lenses, which reflect more light than basic plastic CR-39 or glass lenses.

What to know: AR may get a bad rap from consumers who remember it being prone to degrading and developing cracks called “crazing” or “spiderwebbing” in its earlier days. But, according to Vitale, such problems were mostly resolved at the beginning of the 2000s. In the past, AR coatings also tended to attract dust and grime, but they now generally include an anti-static treatment that helps repel water and oil and keeps the coating cleaner. “Most of the AR coatings on the market today perform extremely well,” Vitale says.

Two phenomena play an important role in the context of natural optical activity, that is to say, optical activity that occurs without applying magnetic fields and such. One of them is optical rotation. Optical rotation means the the plane of polarization of a linearly polarized light beam rotates as it passes through an optically active medium such as a solution of chiral molecules. The rotation angle is proportional to the path length through the medium, and in case of a solution it is also proportional to the concentration of the chiral substance.

Elliptical polarization

And while some coatings may be included in your eyeglass package price, others may add as much as $100-plus to your bill.

Identically prepared solutions of the two enantiomers of a chiral molecule rotate the polarization plane in equal but opposite directions. A mixture of equal amounts of the two enantiomers (racemate) or a nonchiral substance does not exhibit this effect. However, the sign of the rotation is not in a simple way related to the chiral structure in the sense that, say, a D configuration would always have a positive or negative optical rotation. Therefore, without additional structural information it is not possible to deduce an unknown absolute configuration of a molecule simply from the sign of the optical rotation. Quantum theoretical calculations are very useful in this case.

© 2005 – 2024 J. Autschbach. The material shown on this web page is in parts based on the results of research funded by grants from the National Science Foundation (NSF, CHE 0447321, 0952253) and educational projects supported by these grants. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.

To help you sort through the common choices, we’ve gathered advice and cost information from vision experts and major eyeglass retailers, and December 2019 VisionWatch market research from the Vision Council, a nonprofit trade association for the optical industry.

Ask for an itemized description. In many cases, eyeglass lenses come bundled with certain coatings, commonly those that reduce reflections or bolster scratch resistance. Be sure you don’t pay extra for a coating that’s already supposed to be part of your package.

by B Herman · 1993 · Cited by 9 — multilevel Fresnei tO the Fresnel values are compared, we find the ratios to be 0.95 at all the wavelengths, showing that using only three binary masks ...

Avoid the hard sell. Even if you’re buying the glasses from your ophthalmologist, “by the time you get to the eyeglass purchase point in the eye exam cycle, you’re in a retail environment and may be working with the staff, rather than the doctor,” Vitale says.

Here, dyes are applied to lenses to cut down on the visible light (but not necessarily UV rays) entering the eye. Hues range from light tints like a pastel blue or pink to deeper shades used for sunglasses.

CCTV & Machine Vision Lenses ; Computar C-Mount 12.5-75mm Varifocal Lens. B&H # COM6Z12123S MFR # M6Z1212-3S · $309 ; Computar A4Z2812CS-MPIR CS-Mount 2.8-10mm ...

Another important phenomenon that is only observed for chiral substances is called circular dichroism (CD). In a nutshell, if we record the electronic absorption spectrum (typically in the UV-Vis range) of a chiral substance with circularly polarized light (see explanations below) instead of linearly polarized light, the spectra for one of the enantiomers recorded with left or right circularly polarized light differ slightly. Compare the red and green curves in the image below. (See the next paragraph for some animations of circularly and elliptically polarized waves and further explanations). If we plot the difference between the two absorption spectra we have what is called the CD spectrum shown in the graphics below in blue (here: ‘red minus green’). The CD spectrum (the Δ𝜀 curve) for the other enantiomer would have the opposite sign, i.e. we would obtain the blue curve mirrored at the horizontal axis. Nonchiral substances do not exhibit CD except in the presence of a static magnetic field (Faraday effect).

Who might consider: People who just like the look, of course. But tints may also help improve contrast for those with degenerative retinal disorders or light sensitivity. “Tinted lenses may reduce discomfort in bright light,” Brodie says. In some cases, even light tints may increase contrast, which can be helpful to pilots and marksmen working in outside light, he says.