diffraction-limitedspot size formula

Although the above diagrams help give a feel for the concept of diffraction, only real-world photography can show its visual impact. The following series of images were taken on the Canon EOS 20D, which typically exhibits softening from diffraction beyond about f/11. Move your mouse over each f-number to see how these impact fine detail:

Abbediffractionlimit derivation

For an ideal circular aperture, the 2-D diffraction pattern is called an "airy disk," after its discoverer George Airy. The width of the airy disk is used to define the theoretical maximum resolution for an optical system (defined as the diameter of the first dark circle).

Blue light filtering lens treatment is among the available eye protection technologies we offer. Many digital LED screens emit blue light, which may contribute to glare and discomfort after extended use.

In practice, the diffraction limit doesn't necessarily bring about an abrupt change; there is actually a gradual transition between when diffraction is and is not visible. Furthermore, this limit is only a best-case scenario when using an otherwise perfect lens; real-world results may vary.

Wearing blue light filtering glasses during prolonged computer or tablet use can filter some blue-violet light and may enhance your sense of visual comfort.

However, if your eyes are exposed to long-term UV radiation without proper protection, you may be at a greater risk of developing cataracts and/or macular degeneration later in life.

Light rays passing through a small aperture will begin to diverge and interfere with one another. This becomes more significant as the size of the aperture decreases relative to the wavelength of light passing through, but occurs to some extent for any aperture or concentrated light source.

Diffraction is an optical effect which limits the total resolution of your photography — no matter how many megapixels your camera may have. It happens because light begins to disperse or "diffract" when passing through a small opening (such as your camera's aperture). This effect is normally negligible, since smaller apertures often improve sharpness by minimizing lens aberrations. However, for sufficiently small apertures, this strategy becomes counterproductive — at which point your camera is said to have become diffraction limited. Knowing this limit can help maximize detail, and avoid an unnecessarily long exposure or high ISO speed.

Yes! In fact, if you opt for glasses without 100% UV protection, you may as well not wear sunglasses at all. Adding a UV coating to your Rx lenses is easy, and often comes free with the lenses you order from FramesDirect.com.

Some diffraction is often ok if you are willing to sacrifice sharpness at the focal plane in exchange for sharpness outside the depth of field. Alternatively, very small apertures may be required to achieve sufficiently long exposures, such as to induce motion blur with flowing water. In other words, diffraction is just something to be aware of when choosing your exposure settings, similar to how one would balance other trade-offs such as noise (ISO) vs shutter speed.

If they are made with polycarbonate or a similar material, safety glasses may naturally block UV radiation. If not, a UV-protective coating can likely be added during production when you order a new pair.

Note: CF = "crop factor" (commonly referred to as the focal length multiplier); assumes square pixels, 4:3 aspect ratio for compact digital and 3:2 for SLR. *Calculator assumes that your camera sensor uses the typical bayer array.

FramesDirect offers thousands of sunglasses and eyeglasses from top designers and brands. Contact us with any questions about specific frames or how to add UV coating to your glasses.

Our clear, UV-protective lens coating blocks 100% of harmful UVA and UVB rays and comes standard on all polycarbonate and high-index lenses. Without changing the color of the lens, the coating will help defend your eyes against UVA and UVB rays.

The sun poses the biggest daily threat when it comes to ultraviolet radiation. However, welding equipment, tanning beds, and lasers can also produce UV rays. They may require special eye protection beyond regular sunglasses, so make sure you have the right gear.

Choose sunglasses that offer 100% UV protection and they will likely also filter out some blue-violet light, also known as high-energy visible (HEV) light rays.

Even when a camera system is near or just past its diffraction limit, other factors such as focus accuracy, motion blur and imperfect lenses are likely to be more significant. Diffraction therefore limits total sharpness only when using a sturdy tripod, mirror lock-up and a very high quality lens.

Diffraction limitedtelescope

Adding a UV coating and blue light filtering coating to your eyeglasses will filter out much of the blue-violet light emitted from LED screens as well. Since blue-violet light is emitted from LED screens, and UV rays and blue-violet light are emitted from the sun, it may be worthwhile to opt for both coatings to ensure extra protection.

For additional reading on this topic, also see the addendum: Digital Camera Diffraction, Part 2: Resolution, Color & Micro-Contrast

The form below calculates the size of the airy disk and assesses whether the camera has become diffraction limited. Click on "show advanced" to define a custom circle of confusion (CoC), or to see the influence of pixel size.

This is called photokeratitis, and it can make your eyes become red and puffy. It can also make your eyes feel gritty, like you might have sand in them. If you’re very sensitive to light, you may suffer from excessive tearing. Fortunately, these symptoms are usually temporary.

It’s possible for UV protection to decrease after years of wear, so it’s a good practice to replace your eyewear every few years. When shopping for the right style, make sure to consider the fit and temple coverage as well. These elements can provide additional protection for people regularly exposed to heavy, direct sunlight.

Since the size of the airy disk also depends on the wavelength of light, each of the three primary colors will reach its diffraction limit at a different aperture. The calculation above assumes light in the middle of the visible spectrum (~550 nm). Typical digital SLR cameras can capture light with a wavelength of anywhere from 450 to 680 nm, so at best the airy disk would have a diameter of 80% the size shown above (for pure blue light).

While most commonly seen as rectangular frames, you can find sleek wraparound styles with oval and rounded lenses. Some of our top performance brands, including Smith, Oakley, and Maui Jim, make wraparound frames with 3-, 5-, and 8-base wraps. These ensure your frames stay balanced and comfortable through high-octane activities while providing the most protection possible.

No amount of lens cleaning or exposure to heat will affect the protective qualities of sunglasses with UV protection embedded. Choose a brand known for the quality of its lenses—like Wiley X, Maui Jim, or Ray-Ban—to get sunglasses that come standard with UV protection.

Note: above airy disk will appear narrower than its specified diameter (since this is defined by where it reaches its first minimum instead of by the visible inner bright region).

Ideally, your sunglasses should be labeled as UV400 or providing 100% UVA-UVB protection against the sun’s UV rays. You should be able to verify from the sticker or product information included with a pair of sunglasses how much UV protection they provide.

Technical Note: Independence of Focal Length Since the physical size of an aperture is larger for telephoto lenses (f/4 has a 50 mm diameter at 200 mm, but only a 25 mm diameter at 100 mm), why doesn't the airy disk become smaller? This is because longer focal lengths also cause light to travel farther before hitting the camera sensor -- thus increasing the distance over which the airy disk can continue to diverge. The competing effects of larger aperture and longer focal length therefore cancel, leaving only the f-number as being important (which describes focal length relative to aperture size).

Wraparound, or sunglasses with a wrapped profile are the best sunglasses for UV protection because they offer the most coverage. This style of frame curves around your features to provide ample protection from straight-on and peripheral sunlight.

Camera Canon EOS 1Ds Canon EOS 1Ds Mk II Canon EOS 1Ds Mk III, 5D Mk II Canon EOS 1D Canon EOS 1D Mk II Canon EOS 1D Mk III Canon EOS 1D Mk IV Canon EOS 1D X Canon EOS 5D Canon EOS 5D Mk III Canon EOS 7D,60D,550D,600D,650D,1D C Canon EOS 50D, 500D Canon EOS 40D, 400D, 1000D Canon EOS 30D, 20D, 350D Canon EOS 1100D Canon PowerShot G1 X Canon PowerShot G11, G12, S95 Canon PowerShot G9, S100 Canon PowerShot G6 Nikon D3, D3S / D700 Nikon D40, D50, D70 Nikon D4 Nikon D60, D80, D3000 Nikon D3X Nikon D2X, D90, D300, D5000 Nikon D800 Nikon D5100, D7000 Sony SLT-A65, SLT-A77, NEX-7 Sony DSC-RX100

Sunglasses can reduce some of your exposure to blue light, but they may not block the entire spectrum of blue light. Certain sunglasses tints, such as dark amber, are most effective at reducing the amount of blue light exposure from a digital screen.

Since the divergent rays now travel different distances, some move out of phase and begin to interfere with each other — adding in some places and partially or completely canceling out in others. This interference produces a diffraction pattern with peak intensities where the amplitude of the light waves add, and less light where they subtract. If one were to measure the intensity of light reaching each position on a line, the measurements would appear as bands similar to those shown below.

As a result of the sensor's anti-aliasing filter (and the Rayleigh criterion above), an airy disk can have a diameter of about 2-3 pixels before diffraction limits resolution (assuming an otherwise perfect lens). However, diffraction will likely have a visual impact prior to reaching this diameter.

This calculator shows a camera as being diffraction limited when the diameter of the airy disk exceeds what is typically resolvable in an 8x10 inch print viewed from one foot. Click "show advanced" to change the criteria for reaching this limit. The "set circle of confusion based on pixels" checkbox indicates when diffraction is likely to become visible on a computer at 100% scale. For a further explanation of each input setting, also see the depth of field calculator.

Diffraction limited systemwikipedia

Diffraction limited systempdf

Gamers and computer users who spend long hours on a screen may even want to opt for lenses in a bronze, copper, or reddish-brown tint to filter out a larger spectrum of blue light and enhance their eye comfort.

Your lens material can provide some protection too. Polycarbonate lenses and other high-index plastics like Trivex inherently provide 100% UV protection. However, regular plastic lenses must have a UV coating added to make them UV-protective.

Note how most of the lines in the fabric are still resolved at f/11, but have slightly lower small-scale contrast or acutance (particularly where the fabric lines are very close). This is because the airy disks are only partially overlapping, similar to the effect on adjacent rows of alternating black and white airy disks (as shown on the right). By f/22, almost all fine lines have been smoothed out because the airy disks are larger than this detail.

Photochromic lenses — the ones that darken automatically when exposed to direct sunlight — already have UV protection embedded in them.

When the diameter of the airy disk's central peak becomes large relative to the pixel size in the camera (or maximum tolerable circle of confusion), it begins to have a visual impact on the image. Once two airy disks become any closer than half their width, they are also no longer resolvable (Rayleigh criterion).

Diffraction limited systemapplications

If you plan to step outside in your glasses without switching to shades, a UV coating is an important option to consider. Fortunately, lenses don’t need a dark tint to provide 100% UV protection. The UV coating is effective at blocking UV radiation whether you have clear lenses or tinted sunglasses.

Yes. A UV coating on eyeglasses and sunglasses protects your eyes from harmful ultraviolet radiation. Even short-term exposure to ultraviolet radiation without wearing UV-protective sunglasses or eyeglasses can cause damage in your eyes that is similar to a sunburn.

Be sure to double-check product details to ensure you’re getting full coverage. FramesDirect offers a UV coating that can be added at checkout, so no matter what frames you choose, you can be certain your eyes are shielded from 100% of the sun’s harmful rays.

Camera Type Digital SLR with CF of 1.6X Digital SLR with CF of 1.5X Digital SLR with CF of 1.3X Digital SLR with 4/3" sensor 35 mm (full frame) Digital compact with 1/3" sensor Digital compact with 1/2.3" sensor Digital compact with 1/2" sensor Digital compact with 1/1.8" sensor Digital compact with 2/3" sensor Digital compact with a 1" sensor APS 6x4.5 cm 6x6 cm 6x7 cm 5x4 inch 10x8 inch

This should not lead you to think that "larger apertures are better," even though very small apertures create a soft image; most lenses are also quite soft when used wide open (at the largest aperture available). Camera systems typically have an optimal aperture in between the largest and smallest settings; with most lenses, optimal sharpness is often close to the diffraction limit, but with some lenses this may even occur prior to the diffraction limit. These calculations only show when diffraction becomes significant, not necessarily the location of optimum sharpness (see camera lens quality: MTF, resolution & contrast for more on this).

Polarization refers to a lens’s ability to reduce glare and haze in bright sun. While the sun’s rays often hit you directly, they can also reflect off of water, sand, snow, and buildings. Polarized lenses tend to be most helpful for reducing glare around these reflective surfaces.

There are three types of ultraviolet radiation: UVA, UVB, and UVC. Both UVA and UVB rays (or simply, UV radiation) can cause short- and long-term damage to your eyes and your vision. This makes UVA and UVB rays the target for UV protection in glasses and sunglasses. UVC radiation is considered a minimal threat because it’s absorbed by the earth’s ozone layer.

The size of the airy disk is primarily useful in the context of pixel size. The following interactive tool shows a single airy disk compared to pixel size for several camera models:

Diffractionlimit formula

No. Polarization and UV protection are different, so it’s important to make sure that UV protection is included when shopping for polarized sunglasses. It’s common for companies to advertise them together because polarization is typically only offered with sunglasses. But remember: Polarization alone does not protect your eyes from UV radiation.

UV protection is accomplished by adding a coating to sunglasses and eyeglasses lenses during the manufacturing process. This UV coating blocks the sun’s harmful ultraviolet radiation, keeping it from your eyes and the delicate skin around them. UV protection on your glasses and sunglasses lenses helps protect your eyes from the damage UV radiation can cause.

Even if sunglasses are dark enough to block visible light, that does not automatically mean they provide protection from UV radiation. It can actually be more harmful to wear dark shades without UV protection than to not wear any sunglasses at all. This is because the dark tint may allow your pupils to remain larger in the sun, which can expose your eyes to more damage from UV radiation.

Another complication is that sensors utilizing a Bayer array allocate twice the fraction of pixels to green as red or blue light, and then interpolate these colors to produce the final full color image. This means that as the diffraction limit is approached, the first signs will be a loss of resolution in green and pixel-level luminosity. Blue light requires the smallest apertures (highest f-stop) in order to reduce its resolution due to diffraction.

Airy Diameter: 21.3 µm Camera Canon EOS 1Ds Canon EOS 1Ds Mk II Canon EOS 1Ds Mk III, 5D Mk II Canon EOS 1D Canon EOS 1D Mk II Canon EOS 1D Mk III Canon EOS 1D Mk IV Canon EOS 1D X Canon EOS 5D Canon EOS 5D Mk III Canon EOS 7D,60D,550D,600D,650D,1D C Canon EOS 50D, 500D Canon EOS 40D, 400D, 1000D Canon EOS 30D, 20D, 350D Canon EOS 1100D Canon PowerShot G1 X Canon PowerShot G11, G12, S95 Canon PowerShot G9, S100 Canon PowerShot G6 Nikon D3, D3S / D700 Nikon D40, D50, D70 Nikon D4 Nikon D60, D80, D3000 Nikon D3X Nikon D2X, D90, D300, D5000 Nikon D800 Nikon D5100, D7000 Sony SLT-A65, SLT-A77, NEX-7 Sony DSC-RX100 Pixel Diameter: 6.9 µm

UV-protective sunglasses and glasses feature a thin coating of UVA- and UVB-blocking material to protect your eyes outdoors. This UV coating can be applied to any plastic or glass lens for maximum protection. UV protection is so important that FramesDirect provides this UV-protective coating on all of our lenses at no additional cost.

As two examples, the Canon EOS 20D begins to show diffraction at around f/11, whereas the Canon PowerShot G6 begins to show its effects at only about f/5.6. On the other hand, the Canon G6 does not require apertures as small as the 20D in order to achieve the same depth of field (due to its much smaller sensor size).

Diffraction limited systemformula

Are smaller pixels somehow worse? Not necessarily. Just because the diffraction limit has been reached (with large pixels) does not necessarily mean an image is any worse than if smaller pixels had been used (and the limit was surpassed); both scenarios still have the same total resolution (even though the smaller pixels produce a larger file). However, the camera with the smaller pixels will render the photo with fewer artifacts (such as color moiré and aliasing). Smaller pixels also give more creative flexibility, since these can yield a higher resolution if using a larger aperture is possible (such as when the depth of field can be shallow). On the other hand, when other factors such as noise and dynamic range are considered, the "small vs. large" pixels debate becomes more complicated...

Blue-violet light is between 400 nm and 455 nm as stated by ISO TR20772-2018. (ISO: International Standards Organization – “Ophthalmic optics – Spectacles lenses – Short Wavelength visible solar radiation and the eye, FD ISO/TR 20772”)

Diffraction thus sets a fundamental resolution limit that is independent of the number of megapixels, or the size of the film format. It depends only on the f-number of your lens, and on the wavelength of light being imaged. One can think of it as the smallest theoretical "pixel" of detail in photography. Furthermore, the onset of diffraction is gradual; prior to limiting resolution, it can still reduce small-scale contrast by causing airy disks to partially overlap.