Spherical lens for optics : a complete guide

Spherical lens refers to a type of optical lens with one or two surface shaped like a cut of sphere, meaning this surface can be defined from a center reference point and a fix radius of curvature.  Spherical lens are the more commons form of optical lens, being easier to design, easier to manufacture and easier to check the quality. Learn more about spherical lens how they are used and manufacture in below guide.

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What are spherical lenses used for?

Spherical lens are used in applications where light will be converged or diverged to form a smaller or bigger image of an object / field of view.

For example on a camera, lenses are used to focus the image of an object which is close or far from the device on a sensor (often a CMOS) of several mm wide. If you are taking a picture of a building, this building image will be shrink at exact proportions from several meters to several mm and transcribe into digital information so you would be ablet to print it.

On the opposite on a microscope the lens will enlarge a very small object to a wider image that can be seen either by raw eye on a eye piece or by a digital sensor.

What are the types of spherical lenses?

Spherical lenses are usually defined by the shape of their two surfaces, which is mix of flat, concave, and convex.

Illustration 1 : a Plano-concave lens (PCV lens), with a flat surface and a spherical concave surface (with radius of curvature of 140mm in this example.

Illustration 2 : a plano-convex lens (PCX lens), with a flat surface on the right and a spherical convex surface on the left with a radius of curvature of 36mm in this example.

Illustration 3:  meniscus lens, thin lens with with a concave spherical surface on the left and a spherical concave surface of the on the right.

Illustration 4: a biconvex lens with two surface of spherical convex surface with a radius of curvature of 80,5mm for both sides in this example.

Illustration 5 : a biconcave lens with two spherical concave surfaces and a center thickness of 1,8mm in this example.

Remarks :

• It is also commun for some lenses to have one face non spherical and an other face spherical.
• In some publications an optical elements with both faces flat is called “flat lens”, we will not use this term and refer to these elements as optical windows as they are not shaped to converge of diverge the light.

How spherical lenses are made?

Normal process for manufacturing of a spherical lens is as below :

1. Cut or mold a preform close to the shape of the lens
2. Grinding of the part to get the right shape
3. Polishing of both optical surfaces on semi-automatic polishing device
4. Centering / edging of the lens to match the lens mechanical axis and optical axis. Lens centering is very important as bad centering will conduct to degradation of optical properties in the optical system after assembly.
5. Cleaning of the lens with ultrasound cleaning machines
6. Coating of the lens, in a coating device

Which optical material can be used for spherical lens?

Most optical material can be used to manufacture a spherical lens, choice of material should be made according to below criteria :

• Refractive index (define how the light rays will react at the interface of air / lens)
• Abbe number  (define the chromatic dispersion)
• Useful wavelength (UV, visible, IR)
• Point of fusion in case the lens is to be molded
• Availability / cost of material.  Some material may be the exact match for your desing, but they may not be available or extremely expensive, therefore a close equivalent maybe considered.
• Usage conditions : for example under extreme condition extra hard material like sapphire may be chosen.

In case no specific constraint, we advise to design lens with N-BK7 ( Schott)/ HK9L (CDGM) optical glass, they are widely available and relatively cheap.

How much does a spherical lens cost?

Spherical lens can be found from a wide range from less than one USD to several thousand USD per lens. Below are the parameters that impact a lens price :

Parameter Impact on spherical lens cost Raw material Affordable materials : N-BK7/HK9L/B270/ Fused silica/Plastics, to more expensive materials : Sapphire, Germanium, Silicon, very specific optical material Size Very small (less than 5mm) and extra large lenses (more than 100mm) are more expensive to produce due to polishing difficulties related to the size. Optical specifications Polishing quality and surface quality have a very significant impact on the pricing of a spherical lens, and increase of specification can see a component price jumping to an other level Order quantities Polishing of spherical lenses can be done in parallel semi-automatic polishing machines, meaning that it wild take almost the same time and ressources to manufacture one or ten parts. Optical coatings Optical coatings is done per batch, one batch cost usually several hundreds of USD, therefore the more parts you can put in a device the cheaper the unit price will be, contact us for the optimum order quatity.

If you are looking for a specific price for your project don’t hesitate to request for a free quotation :

Spherical lens focal length

The focal point of a spherical lens is the point on the optical axis at which an incident bundle of light rays will converge to focus.

The focal length, is the distance between the center of the lens and the focal point. The focal length is a positive value in case of converging lens, and negative in term of diverging lens.

According to the shape of the surfaces, a spherical lens can be diverging or converging.

The focal length formula (Gaussian formula) is :

1/u + 1/v = 1/f

Where :

u : is the distance of the object to the center of the lens

v: is the distance of the image to the center of the lens

f: is the focal length.

For example with an objet at the infinity, we will have 1/u that tend toward 0, so 1/v=1/f so v=f, the image will form at the focal length.

A spherical lens is defined by it’s optical power which is inverse equivalent to the focal length, meaning that the closer to the lens the focal point is the higher the power of the length.

P=1/f

Where P is the power of the lens and f the focal length.

The simulation of a spherical lens focal length can be done based on the refractive index of the material (Snell law), thickness of the lens and radius of curvature. As the calculus is little complicated we advise spherical lens users to use simulation software (like Zemax) to get a reliable value.

Spherical lens concentricity, a key specification

An optical lens usually have 2 types of tolerancing :

For more information, please visit Optical Spherical Lenses For Imaging.

1. optical tolerancing
2. mechanical tolerancing

Concentricity is a direct link between both. Lens concentricity will define how close the optical center will be to the mechanical center,  this is particularly important in an optical system involving several lenses assembled in the same mechanical barrel as concentricity error of each lens may adds up.

Aspheric lenses are a new optical technology that is improving images from cameras, telescopes, and other optical devices. These lenses are also being applied to personal visual devices, most often glasses.

This type of lens can be made from any material, including polycarbonate and Trivex. Because they have a different, non-spherical design, they can improve how light refracts onto your retina while allowing you to wear a lighter material with less curvature. This means they are less likely to create the “coke bottle glasses” effect.

People who have higher order refractive errors, usually +4.00 diopters or more, benefit the most from aspherical lenses. Reading glasses and contact lenses are also being manufactured with this type of lens, so more people can benefit from clearer vision. Aspherical intraocular lenses (IOLs), which are implanted during cataract removal surgery, are also being recommended to manage refractive errors.

There are a few downsides to aspherical lenses. The main issue is their cost since they take more effort to manufacture. These lenses may also require reflective coatings that traditional lenses do not, and they require accurate measurements of your pupillary distance.

Aspheric Lenses: Better Vision & Better Appearance

Aspheric lenses are a thinner, flatter type of lens for glasses. In the past, people who have higher prescriptions have needed thicker lenses to see clearly. Thanks to changes in the materials and technology of glasses, even people who are very nearsighted or farsighted can wear lightweight glasses and thin frames.

This is much more convenient for people who wear glasses. These thinner lenses are more attractive, and they feel better resting on the face.

These lenses are like those used for cameras. Originally, both concave and convex lenses for cameras were designed to represent part of a perfect sphere. However, these lenses cannot project an image that is uniformly focused across a flat surface, even in various combinations. This is because the depth of focus is too narrow. When applied to cameras, aspherical lenses correct these focus aberrations.

Like aspheric camera lenses, aspheric glasses lenses improve the evenness of your focus. Thanks to adaptations in computer models of these lenses and improved manufacturing techniques, aspheric lenses are more common across dozens of applications, including for vision improvement. Many people who need glasses are switching to aspheric lenses for the vision benefits, comfort, and improved appearance.

What Are Aspheric Lenses? How Are They Different From Traditional Lenses?

The term aspheric means “not spherical,” which shows the main difference between these lenses and traditional lenses for glasses. Traditional lenses made from glass or plastic tend to have a slightly bulged shape, mimicking a sphere. These older designs follow a curve like that of your eye’s cornea and lens, to adjust how light is refracted onto your retina.

Traditional lenses can be large and heavy if you have a significant refractive error, like astigmatism, myopia, or hyperopia. Traditionally, lens shapes are:

• Convex, or thicker at the center and thinner at the edges, to improve farsightedness (hyperopia and presbyopia).
• Concave, or thinner at the center and thicker around the edges, to improve nearsightedness (myopia).

When lenses treat higher order vision problems, traditional lenses are thicker in some areas, which creates the “coke bottle lens” effect. Many people find this unattractive and avoid wearing their glasses as a result. They may choose an alternative like contact lenses or LASIK, or they may simply avoid wearing their glasses, which can increase eye strain.

Traditional lenses for glasses are also prone to spherical errors. These imaging errors or aberrations can create slightly blurry images since the light rays do not converge at one single point on the optical axis, which should be your retina. Light rays are refracted at slightly different degrees from different angles, depending on where they enter the eye through the lens. They collect in the general area of your retina, but the light could still be distributed so it does not create a clear image in your brain.

Other problems with spherical lenses can include:

• Marginal astigmatism. This occurs when narrow beams of parallel rays hit your lens at an angle, creating two focus points. This can create an astigmatism effect even if you do not have an astigmatism.
• Distortion. This is when light rays move from the center of the lens to the edges, increasing magnification. This can cause a distortion in your visual field known as the pincushion effect.

• Chromatic aberration. This is when light moving through the lens is dispersed or broken up into component colors. Each wavelength travels at a different speed, causing some objects to appear a slightly different color.

In contrast, aspheric lenses are rotationally symmetric, with one or more nonspherical surfaces that differ from a sphere’s shape. This improves how aberrations are corrected, so light rays are refracted on a more accurate point on your retina.

Who Should Wear Aspheric Lenses?

Many people now opt for aspheric lenses because of their stylistic build and wide range when pairing with frames. However, these lenses offer more than just style and aesthetic value

Anyone with a higher order refractive error can benefit from aspheric lenses. This is typically around +4.00 diopters or higher. Traditional glasses become bulky and heavy because they must be thick enough to correct curvature problems in your cornea or lens. Aspheric lenses can correct these refractive issues more effectively.

Benefits of aspheric lenses include:

• They correct spherical aberration and make images less blurry
• They improve image quality
• They offer improved peripheral vision
• They are light and comfortable to wear
• More frame options for people with strong prescriptions
• They come in a thinner and slimmer profile

While people who wear glasses benefit the most from aspheric lenses, contact lens manufacturers are also creating aspheric contacts, offering a similar, lower distortion effect. These are great for people with more active lifestyles who want or need a full range of view, including peripheral vision, which glasses may not correct.

More reading glasses are being made with aspheric lenses too. Although aspheric lenses are recommended for people who need vision correction all the time, reading glasses at lower diopters can also benefit from being aspheric, especially if they are progressive lenses rather than bifocals.

Aspheric Intraocular Lenses (IOLs)

If you have cataracts that obscure your vision, you are likely to be recommended for cataract surgery. This process removes the natural lens of your eye and replaces it with an artificial lens, called an intraocular lens (IOL).

For some people, these lenses can lead to refractive errors even when one did not exist before. This is because they do not refract light as well as a healthy natural lens. It can be difficult to predict how serious the refractive error will be because cataract surgery does not involve mapping the cornea, which refracts light too. If there is a shape change on the cornea, a refractive error can also develop.

Some surgeons offer aspherical IOLs to offset potential refractive errors. A study measured preoperative corneal topography. Then, doctors chose an aspherical IOL based on the existing corneal aberrations, so that the sum of the two values was as close to zero as possible. While some surgeons are skeptical about the precision of aspheric IOL manufacturing measurements, approaching cataract surgery in this way can improve visual acuity outcomes for many people.

Are There Downsides to Aspheric Lenses?

While aspheric lenses are a great option for many people who wear glasses, it is important to make sure the center of the lens lines up with your pupil. Particularly with this type of lens, your vision can become distorted if the pupillary distance is off-center.

Aspheric lenses are also more likely to have reflections, so it is important to get an anti-reflective coating on the lenses. This means that your lenses may cost more than traditional lenses made from plastic. Since aspheric lenses are a specific design or shape and not a type of material, you can get high-quality polycarbonate or even Trivex lenses that are aspheric. These can offer improved visual acuity.

The biggest pitfall with aspheric lenses is their cost. Since there is more precision involved in the manufacturing process, they are harder to manufacture. As they become more common, this cost will likely decrease over time. Right now, spherical lenses are still simpler to make, and they typically cost less.

How to Find Aspheric Lenses

Aspherical lenses are available in many places. Your best best is to buy your lenses through your eye doctor’s office to ensure safety and quality. If you purchase them at a store separately, you can find these options online or at a brick-and-mortar retailer.

Some online retailers, for example, will ask during the glasses ordering process whether you want to upgrade to thinner, aspheric lenses for an additional charge. However, online retailers may not be able to get your pupil distance lined up properly, so purchasing these lenses in person may work better. You can ask a retailer in person about this option.

If you do opt to order these lenses online, confirm the retailer’s return policy if the pupillary distance isn’t correct. You don’t want to be stuck with lenses that don’t work for you.

Best Aspheric Lens Brands in

While still relatively new, aspheric glasses are widely accepted and recognized by eyewear professionals and eyeglass wearers. Some of the standout brands that provide quality aspheric lenses include:

1. LaCroix Precision Optics: Established in , this manufacturer is regarded as one of the leading aspheric lens service providers. Based in Batesville, Ark., it can customize your aspheric lenses based on your unique eye shape and preferences.
2. Fresnel technologies Inc.: Founded in , the company deals in IR transmitting materials and optics and molded plastic optics. Located in Fort Worth, Texas, the firm is one of the pioneer manufacturers of aspheric lenses.
3. Hitachi Hicg-Tech America Inc.: Founded in , this organization has a solid track record of providing quality eyewear solutions. It is based in Schaumburg, Ill., and deal in aspheric lenses, prisms, and mirrors.
4. Shanghai Optics Inc.: Located in Clark, N.J., this group deals in manufacturing various advanced optical assemblies and components.

Before choosing your preferred aspheric lenses provider, you should consult an optometrist to determine which brands work best for your eye condition.

Contact us to discuss your requirements of Coating Witness Samples Wholesaler. Our experienced sales team can help you identify the options that best suit your needs.