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.

Understanding the purpose of an MTF chart and how to read and MTF chart is an essential skill for anyone involved in the development of products that use optics.

Usually MTF chart includes two plots for selected off axis points of field of view. There is a very small difference because of different apture value from Meridional and sagittal apertures., this come from tilt and other geometrical issues.

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.”

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.

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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.

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.

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.

LensMTFdatabase

MTF stands for modulation transfer function, this means the transferring of differing optical spatial frequencies through an optical systems.

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.

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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.

When optical system posses big residual aberrations then calculation of MTF is loosing accuracy. Reasonable limit is wavefront deviation in 1 lambda.

With over 15 years of experience and 500+ unique optical systems designed, Optics for Hire specializes in advanced optical engineering. If it uses light, we've worked on it.

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.

Modulation transfer function

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.

mtf: image quality

Residual aberration deviates wave fronts going from the object when compared with ideal system. However there is criteria when real optical system can be regarded as ideal. It is similar to tolerance which provides that. This criteria names as Rayleigh λ/4. It means that absolute value of wavefront deviation in optical system has to be not exceed quarter (fourth) of wavelength value. In this example ideal MTF in black, real in blue.

In image below, the upper half is a sinusoidal test object and the lower half is an object imaged by a real optical systems. The upper half has perfect contrast the lower half is contract is reduced because of diffraction.

FujifilmMTFcharts

An ‘Ideal’ optical system is one which transfers optical wave fronts from an object without any deviations. But in any real optical system there is a limit to apeture and and apeture creates diffraction which reduces MTF. As the diffraction spacial frequency grows, the MTF of a system is reduces. An analog in electronics is where devices filter temporary frequencies. MTF of ideal system has formula.

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.

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.

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.

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.”

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.

In this post we will review the definitions, show example charts, impact of sensor, abberrations, Meridional and sagittal plots and diffraction limited optical systems.

But it has slightly lower resolution because of residual aberration which depends on optical performances, number of lens elements and types of glasses.

In real system the difference can be bigger because of residual aberrations. One of the biggest influences is astigmatism.

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.)

The formula for MTF in an ideal optical system where MTF is defined by the diffraction limit. It is show below as a formula and plotted on an MTF chart in the second image

MTFlens

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.

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.

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.”

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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.

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.

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.”

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.

Mtf graphexplained

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

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.

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).

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.

Below are examples of MTF plot from Zemax, on the left image the x axis is spatial in units of line pair per mm and the Y axis is amplitude which also can be called contrast. The different color lines are different fields of view. The black line is plot for ideal system.

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.

With over 20 years of experience and 800+ unique optical systems designed, Optics for Hire specializes in advanced optical engineering. If it uses light, we've worked on it.