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Shanghai Optics produces high precision spherical lenses in plano-convex, double convex, and plano-concave shapes. Both plano convex and double convex lenses are what we call positive lenses; they have positive focal lengths. Plano convex lenses are spherical on one surface and flat on the other. They are often selected when one is working with infinite or near-infinite conjugate, for light collimation applications and monochromatic illumination. Their special shape minimizes spherical aberration up to an approximately 5:1 conjugate ratio, and they are often the most practical choice for demanding applications. In an ideal setup the curved surface would face the infinite conjugate or largest object distance.

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Surface quality ratings are an evaluation of the smoothness of a lens, and enable our spherical lenses to be selected to meet any wavefront and low-scatter requirements. This is especially important for laser applications, as surface imperfection in lenses have the potential to initiate laser-induced damage. The MIL-PRF-13830B rating system most commonly used in spherical lens manufacturing provides both a scratch and a dig number, given in an x-y format. Scratches are assigned a number from 10 to 80, with brightness of allowable scratches increasing as the number increases, and dig numbers represent the diameter of the largest allowable dig in 1/100th of millimeters. The total number of digs may not exceed the diameter divided by 20, and the sum of all scratch lengths with the specified scratch number may not exceed ¼ of the diameter of the optic.The standard quality for most optical applications is 40-20. Precision laser requires 20-10 surface quality.

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To minimize divergence of a collimated beam two factors must be balanced: focal length of the collimating system and size of the light source. Equation 1 approximates the divergence of a collimated beam:

Half balllens

Some level of divergence will always be present when collimating light. In the illustration below, both systems produce collimated light, however, Figures 2 and 4 have more divergence compared to Figures 1 and 3 due to the sources being larger. Figures 2 and 4 can be thought of as a collection of closely spaced ideal point sources. Individually, each point creates a ray bundle of parallel rays, but as a collection the series of “point sources” create a beam with some divergence. The divergence exists because, as the size of the source increases, the source’s distance from the optical axis increases, and thus the resultant ray bundle’s angle increases with respect to the optical axis.

Double convex lenses feature two convex surfaces with equal radii and both horizontal and vertical symmetry. They are ideal to form an image at close conjugates as well as for image relay. At 1:1 magnification, when object and image distance are equal, the symmetry of this lens mean that coma, distortion and chromatic aberration are cancelled out and spherical aberration is minimized. We recommend double convex lenses for applications where conjugate ratios are between 5:1 and 1:5.

Half Balllensfocal length

To achieve ideal collimation, the size of the illumination source must be minimized or the focal length of the collimating system must be increased. Note that as you increase the focal length of the system, the system must be physically further away from the source. This means that less light will be captured by the focusing system and overall power in the resultant beam is decreased.

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Magnifying glasses typically use double convex lenses. When the object distance is close, the rays will be bent toward the focal point at the center of the lens. This causes the virtual image to appear much larger than the real image.

Plano concave lenses have negative focal lengths, and are appropriate for situations where the light rays should diverge after passing through the lens. For instance, in light projection, in beam expansion, or when one wishes to expand an optical system’ focal length. When used with other lenses, the negative spherical aberration can be used to cancel out aberrations created by convex lenses. These lenses feature one flat surface and one that is concave, and in most situations, the curved surface should face the largest object distance. The one exception is in high energy lasers, where the flat surface should be directed toward the infinite conjugate or largest object distance in order to avoid the possibility of a virtual focus.

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Spherical lenses, also known as singlets, are optical lenses with curved surfaces that cause light rays to converge or diverge. They are widely used in imaging applications. Conjugate ratio, lens shape, radius of curvature, lens material, transmission, wavefront distortion, scattered light, and types of coating are all features that must be considered when choosing a lens.

Balllensfocal length

A collimated beam of light is defined when every ray within the beam is parallel to every other ray. To produce collimated light you can either place an infinitesimally small source exactly one focal length away from an optical system with a positive focal length or you can observe the point source from infinitely far away. In the real world, neither of these scenarios are possible. In addition, diffraction theory tells us that even if one of these scenarios were met, there would still be some divergence.

Optical coatings provide fine tuning of the reflection/transmission ratios of our custom spherical lenses, and can also extend the life of optical components. Custom BBAR coatings are available upon request, in single or multi-layer applications.

We offer our lenses in a wide range of substrates, including BK7, Fused Silica, N-SF11, Zinc Selenide, Calcium Fluoride, and Silicon. The material of construction largely determines the wavelength, and custom spherical lens are available for infrared, visible, and ultraviolet applications. For infrared applications in defence and security, environmental, medical or agricultural, ZnSe, ZnS, BaF2, CaF2, MgF2 or germanium substrates are usually selected. For visible wavelengths, we recommend Schott, Ohara, CDGM, or Corning Fused Silica.