The lens maker equation calculator is a tool that aids in the selection of optimal parameters for obtaining a given focal length. Both the geometric parameters and the material’s refractive index may be altered. Continue reading to learn about lens design and uses, as well as how to calculate the focal length using our lens calculator.

Lenses Definitions and formulas

A lens is a refractory optical device that uses refraction to focus or disperse a light beam. A simple lens is made up of a single transparent component, whereas a compound lens is made up of numerous simple lenses (elements) that are generally aligned along a common axis. Ground and polished or molded to the required shape, lenses are produced from materials such as glass or plastic. Unlike a prism, which refracts light without concentrating, a lens can concentrate light to produce an image. Devices that concentrate or disperse waves and radiation other than visible light, in the same way, include microwave, electron, acoustic, and explosive lenses.

Various image equipment, such as telescopes, binoculars, and cameras, require lenses. We can also use them in spectacles as visual aids to address vision problems, including myopia and hypermetropia.

Focal Length

The focal length of a camera lens is one of its most essential properties. But, unfortunately, it’s commonly expressed in millimetres by manufacturers (mm).

The distance between the primary back point and the sensor is referred to as focal length, and it refers to the space between the lens’s centre and the point where the light rays converge in the focal point (to form a sharp picture on a surface of a digital sensor, or 35mm film).

Refractive index

The refractive index of a substance (also known as refraction index or index of refraction) is a dimensionless quantity that specifies how quickly light passes through it in optics. We can write it as:


The speed of light in a vacuum is c, while the phase velocity of light in the medium is v. Water, for example, has a refractive index of 1.333, which means light travels 1.333 times slower in water than in air. When a substance’s refractive index is high, the speed of light in the material drops.

To determine how much light is bent or refractive when it enters a material we use the refractive index. Snell’s law of refraction, n1 sinθ1 = n2 sinθ2, describes the angle of incidence and refraction of a ray crossing the interface between two media with refractive indices of n1 and n2, where θ1 and θ2 are the angles of incidence and refraction, respectively, of a ray crossing the interface between two media with refractive indices of n1 and n2.

The refractive indices also govern how much light is reflective at the interface, as well as the critical angle for total internal reflection, intensity (Fresnel’s equations), and Brewster’s angle.

Lens thickness

To grasp this, you need to be aware that lens thickness is divided into four groups, or “indexes,” which are 1.56, 1.61, 1.67, and 1.74, respectively. The lens will be narrower if the index is greater. As the frame size grows higher, the lens thickness increases exponentially, thus it will be on the side of the lens, which is also the thicker area. As a result, the larger the frame, the thicker the lens will be for the same prescription and lens index.

Lens maker equation

To compute the focal length of a lens in the air we can use the lensmaker’s:



  • for indicating the focal length of a lens we are using the letter f,
  • the Refractive index of the lens material is n,
  • R1 represents the radius of curvature of the lens surface closest to the light source (with the sign, see below),
  • R2 is the radius of curvature of the lens surface distant from the light source, and R1 is the radius of curvature of the lens surface closest to the light source,
  • the letter d stands for the thickness of a lens (the distance along the lens axis between the two surface vertices).

Why do we need lenses?

The topic of why humans require lenses may be answered in a variety of ways. We will list some of them, and they are:

  • The human eye is a natural lens whose focus length is controlled by muscles (they can change the shape of the lens). Some people, however, have eyes with lenses that do not focus light adequately, necessitating the use of spectacles – artificial lenses.
  • We can build microscopes that magnify small things and telescopes that magnify objects that are far away with the right lens configuration. If you want to understand more about the magnification of a basic lens, use our Thin Lens Equation Calculator.
  • A camera is another use of optics. A set of lenses may adjust its focal length (by sliding lenses along with the camera) to focus the picture on the camera film, just as the eye muscles.

Focal length calculator

For estimating the focal length of lens in the air we use the mathematical formula below:

\frac{1}{f}=({n}-{1})\cdot\frac{1}{R1}-\frac{1}{R2}+({n}-{1})\cdot \frac{d}{({n}\cdot{R1}\cdot{R2})}


  • The focal length is f, and the lens material’s refractive index is n.
  • R1 is the curvature radius of the lens surface that is closest to the light source.
  • R2 is the curvature radius of the lens surface that is furthest from the light source.
  • The lens thickness is denoted by the letter d.

If we suppose that the lens is exceedingly narrow (d = 0), we may simplify the equation as follows:


The simpler formula can be used in most circumstances since the lenses are thin enough. Switch to the advanced mode of our calculator if you also wish to adjust the lens thickness. We recommend that you compare the numerical differences between the two equations.

Radii of curvature

For the radius of curvature, we can use a positive or negative value. In a nutshell, a spherical lens is made up of two surfaces: left and right, both of which can be convex or concave. We utilized the Cartesian sign convention in our calculator:

  • Left surface R1 > 0, right surface R2 0 for convex lenses;
  • left surface R1 > 0, right surface R2 > 0 for concave lenses.

Radius of Curvature

In differential geometry, the curvature radius, R, is equal to the reciprocal of the curvature. For a curve, it is the radius of the circular arc that best approximates the curve at that point. A surface’s radius of curvature is the diameter of a circle that best matches a normal section or a group of normal sections.

Lens Curvature

We use the curvature of two optical surfaces to classify lenses. If both surfaces of a lens are convex, then it is biconvex (or double convex, or simply convex). The lens is equiconvex if both surfaces have the same radius of curvature. Biconcave refers to a lens having two concave sides (or just concave). To learn more about radius, check this Radius of a Sphere Calculator.


How do you calculate lens maker?

The lens maker’s formula is as follows:

What is the formula of the lens formula?

The Lens formula is:
according to the Convex Lens equation. It links a lens’ Focal Length to the distance between an object in front of it and the picture created by that item. The ratio of image length to object length is known as lens magnification.

How do you use the lens maker equation?

To manufacture a lens with the desired focal length, the lens maker formula is employed. Two curved surfaces exist in a lens, but they are not identical. If we know the refractive index and radius of curvature of both surfaces, we can calculate the focal length of the lens.

What are n1 and n2 in the lens maker formula?

In the lens maker formula (n1) rarer medium of refractive index and, (n2) a denser medium of refractive index.