An aspheric lens is often known as a non-spherical lens. An aspheric lens is a lens whose surface is not part of a sphere or a cylinder. The complex surface of an aspheric lens reduces or eliminates optical aberrations as compared to a simple lens. A single aspheric lens can replace a combination of simple lenses resulting in a system with a much-reduced size.

A convex lens with one side flat is called a plano-convex lens. The lens found in the human eye is a prime example of a convex lens. Another common example of a convex lens is the magnifying glass that is used to correct hypermetropia or long-sightedness. Convex lenses are used in cameras as they focus the light and produce clear images. Convex lenses are also used in compound lenses which are employed in magnifying devices such as microscopes and telescopes.

Parts of a lensdiagram

A concave lens produces a smaller image for the viewer. The focal point of a concave lens is the point from which the light rays parallel to the axis seem to diverge after passing through the lens. The distance from the optical centre of the lens to the focal point is called the focal length of the lens.

The area of the lens suitable for refraction is called aperture. The aperture of the lens is the effective diameter of its light-transmitting area.

Chromatic aberration occurs due to dispersion. When it occurs, a lens fails to focus all colours on the same point. Chromatic aberration can be observed as colourful fringes around an image. It can be fixed using an achromatic doublet (or achromat).

When an object is imaged off the optical axis of the lens, coma aberration takes place. Coma aberration can be eliminated by taking the curvature of the two lens surfaces that matches the application. Best form lenses can be used for it.

When measuring a flatness by the tactile 3-D coordinate measuring method, it is necessary that a tactile contact of the surface with a measuring head is required.

What is the focal lengthof a lens

There are other types of aberrations, and some of them include field curvature, astigmatism, and barrel and pincushion distortion.

Flatness is the difference between the highest and lowest points of a surface located between two ideal flat (planar) surfaces. The distance between the two planar surfaces defines the flatness tolerance.

In the past, we have used Quelltech solutions for flatness measurement in a wide variety of projects. Here you can find a small excerpt of these projects:

Optical chromatic confocal metrology uses the effect of different refraction of different wavelengths in glass. Measurements with white light and laser interferometry uses the scattering behavior of reflected light to determine a surface structure.

There is always potential for improvement, we will help you with that. Contact us for more information or to make an appointment for a consultation.

QuellTech uses the laser scanning measurement method. Laser profiles with up to 4096 points per profile are recorded. Accuracies of up to 1-2 µm can be achieved.

A simple lens is a single piece of magnifying material, while a compound lens consists of a number of simple lenses arranged along a common axis. Optical aberrations are sometimes found in simple lenses, while this property is eliminated in a compound lens. Another advantage of the compound lens is that the magnification of the lens can be adjusted as per the user’s requirements.

Lenticular lenses are a group of microlenses that are used in lenticular printing. These lenses produce images that have an illusion of depth.

We would like to help you evaluate your specific measurement task. By performing an initial free test measurement of your application, we can make an early assessment of feasibility.

A concave lens is a type of lens with at least one side curved inwards. A concave lens with both sides curved inward is known as a biconcave lens. Concave lenses are diverging lenses, that is, they spread out light rays that have been refracted through them. They have the ability to diverge a parallel beam of light. For a concave lens, the edges are wider than the centre, or the centre is thinner than the edges. Concave lenses are used in spectacles in order to overcome myopia or short-sightedness.

Furthermore, the laser scanning method can also be used to measure coplanarity. For example, one laser scanner scans the top surface of a target and a second laser scanner simultaneously scans the same bottom surface of the target. In this way, the parallelism of these two surfaces to each other can be calculated.

Parts of a lensPhysics

Today, there are different types of lenses available. Generally, they are categorised either as a simple lens or a compound lens.

Lenses are basically magnifying glasses with curved sides. A lens is a piece of transparent glass which concentrates or disperses light rays when passes through them by refraction. Due to the magnifying property, lenses are used in telescopes and other magnifying devices. They are employed in cameras for gathering light rays.

If you have any questions about flatness measurement or would like advice from QuellTech on this topic, we would be happy to help.

Parts of a lensnikon

The power of a lens is a measure of its ability to converge or diverge the incident beam of light. It is given by the reciprocal of focal length.

A lens has two spherical surfaces; these two spherical surfaces form a part of a sphere. The centre of these spheres is known as the centre of curvature.

Parts of a lensand their functions

The QuellTech Q5 laser scanner series combines advantages of small form factors with high resolution and fast scan rate. The Q5 is suitable for measurement applications with limited space and rugged environmental requirements.

A Fresnel lens is a lens whose optical surface is divided into narrow rings. This allows the lens to be much thinner and lighter than conventional lenses.

Parts of a lensexplained

Measuring the flatness of surfaces is of great importance in various applications. Some examples are the testing of sealing surfaces between two bodies, such as the cylinder head gasket in automobiles. Measuring flatness is also an important factor in the production of preliminary products in the metal industry, such as the production of axis guides for measuring systems, or in the production of wafers in the semiconductor industry.

In laser scanning, the optical measurement method used by QuellTech, a surface is continuously scanned with a laser line. The diffuse reflections of the laser line are recorded by a sensor. From the profile data recorded in this way, a computer can record a 3D point cloud of a scanned surface. Laser scanning as an optical measuring method is therefore particularly well suited for checking the surface flatness of starting material, profiles, rails and strip material.

Optical aberration is a property of the lens that causes distortion or blurriness during image formation. When it occurs, the light is dispersed or spread out rather than being focused on a certain fixed point. Optical aberration is an undesirable property of lenses and can be eliminated by using a combination of lenses rather than using a single piece of lens.

The QuellTech Q6 Laser Scanner product series has a proven track record in demanding industrial applications that require high levels of precision, process stability and high travel speeds.

LensHood

Parts of a lenseye

In the real world, flatnesses of a few nanometers can be achieved, e.g. for highly polished flat glass surfaces. For metallic measuring objects, which are manufactured in large quantities using the usual production methods, flatness tolerances of a few µm to a few tenths of a mm are common.

A concave lens always generates a virtual image. It can never form a real image. The image is always formed on the same side of the lens as the object, and thus can be seen in the lens only. It cannot be formed in a screen, and as the distance of the object from the optical centre increases, the size of the image decreases.

One of the primary reasons for the occurrence of spherical aberration is that the spherical surfaces of the lens are not the ideal shape, and as a result, the beams are parallel to but distant from the lens axis. This causes the blurring of the image. Spherical aberration can be corrected using a normal lens having the right surface curvatures for a particular application.

In cameras, not one but a group of lenses are used for the gathering of light. Magnification of a lens is the relation between the size of the image formed and the size of the object. Lenses can also be used in groups in order to avoid the blurriness or distortion caused to the image formed by the lens.

The centre of the spherical refracting surface of the lens is called the pole. It is the point where the principal axis meets the surface of the lens.

When a linear object is placed perpendicular to the principal axis of the lens, a linear image is formed perpendicular to the principal axis due to the refraction of the lens. The position, size and nature of the image formed depend on the position of the object with respect to the lens.

Lenses that have a curvature along only one axis are classified as cylindrical lenses. Their main purpose is to convert laser diode elliptical light into a round beam or to focus light into a line. Motion picture anamorphic lenses are an example of such lenses.

There are several types of aberrations, such as spherical aberration, chromatic aberration and coma aberration, that can all affect image formation and quality.

A surface is flat if it has no structures in its surface over its entire length and width. These structures can look as follows:

The tactile scanning step method, on the other hand, performs the flatness measurement with the aid of a contacting measuring head. This measurement is very well suited for very small measuring distances where maximum precision is required. Since the probe head usually has a spherical shape with a certain diameter, it cannot plunge into any small valley of a few µm.

A convex lens is a lens with an outward curve. Unlike the concave lens, the thickness at the centre of a convex lens is more than the thickness at the edges of the lens. Convex lenses are converging lenses. They have the ability to converge a parallel beam of light into a point. This point is called the focal point of the convex lens, and the distance from the optical centre to the focal point is called the focal length. The focal point is on the opposite side of the lens from which the light rays originate.

In contrast to tactile measuring methods, it is possible to record several million measuring points in a few seconds on an area of e.g. 50 x 100 mm: Flatness measurement in highest precision. This high number of measuring points enables a precise and complete recording of the flatness in a short time. The advantage over tactile measurement is that a laser light can penetrate the smallest surface structures.