What is Aspheric Lens? (A Guide to Optical Aspheric Lens)
9 important parameters you must know before you choose aspheric lenses
The aspheric lens has a better radius of curvature and can maintain good aberration correction to achieve the desired performance. It is necessary to know some important parameters before choosing a suitable aspheric lens.
- Design Wavelength: The wavelength at which the lens works best. Lenses can also be used at other wavelengths. Contact DG optoelectronics to find out how the aspheric lens works at other wavelength.
- Numerical Aperture (NA) : a measure of the maximum angle of light acceptable to aspheric lens NA = sin (Φ).
- Clear Aperture(CA): By design, light can pass through the maximum diameter of the surface. Smaller than the actual spherical diameter, which is the physical aperture (PA) .
- Effective focal length (EFL) : the distance from the main surface to the focal point. The normal tolerance is 1% .
- Magnification: The ratio of image size to object size. The calibration lens is unrestricted.
- RMS WFE: the measurement of the chromatic aberration (error) in a lens. The diffraction limit means that, because of diffraction, the lens is guaranteed to conform to the theoretical limit (the maximum operating level that can be achieved in accordance with the laws of physics) .
- Outside diameter(OD): The diameter of the outer cylinder of the aspheic lens, with a standard tolerance of 0.015 mm.
- Working Distance (WD) : also known as rear focal length (BFL), represents the distance from the back of the lens to the focal point.
- Center thickness(CT): Thickness in the axial direction of the lens.
In order to understand these parameters, it is necessary to know the disadvantages and advantages of aspheric lens, compared with spherical lens. In a word, aspheric lens has unique advantages over spherical lens, so it has been widely used in optical instrument, image and optoelectronics industry, such as digital camera, CD player, high-end microscope.
What is the advantages and disadvantages of aspheric lenses VS spheric lenses?
Generally speaking, the spherical lens is thicker, the imaging through the spherical lens will deform. Aspheric lens, on the other hand, is thinner and lighter, and make a more natural and realistic image. If you are interest to know more details, please check here to get information of disadvantages and advantages of aspheric lens.
how aspheric lenses are fabricated?
The aspherical lens manufacture in the following four forming processes:
- Precision glass molding: The process heats the glass in the high temperature, which makes it malleable, then forms it in an aspheric mold and gradually cools it to room temperature. At present, the precision glass molding is not suitable for producing aspheric lens with diameter larger than 10mm. But new tools, optical glass and the metrology process, are driving the technology. The cost of precision glass molding is high in the early stage of design, and the main cost is used in the development of high precision mould. But in the case of mass production, a large number of high quality products can be amortized over the initial development costs.Precision glass moulding aspheric lens, with mass production and high thermal stability, is suitable for being manufactured with large batch, high quality and high thermal stability.
- Precision polishing: Grinding and polishing is generally applicable to the production of a single aspheric lens, with the improvement of technology, its accuracy is better and better. Precision polishing is controlled by a computer and automatically adjusted to achieve parameter optimization. If better quality polishing is required, magneto-rheologic finishing will be used. Compared with standard polishing, magnetorheological finishing has better performance and shorter time. Precision polishing molding, requiring professional equipment, is currently the first choice of sample production and small batch sample.The precision polishing aspheric lens has the characteristics of short sample preparation period and no need of mould. It is suitable for sample making and small batch sample.
- Mixed molding: Mixed molding aspheric lens is using spherical lens as the base, die-casting on the surface of spherical lens by an aspherical mold and UV curing on a layer of polymer aspherical. The achromatic spherical lens is usually used as the base and a layer of aspherical surface which is die-cast on the surface to eliminate the chromatic aberration and spherical aberration.Mixed molding aspherical lens is suitable for mass production where additional characteristics (elimination of chromatic aberration and spherical aberration) are required.
Mixed molding aspherical lens has the characteristics of spherical aberration and chromatic aberration calibration. It is suitable for manufacturing of wide spectrum, large batch and high quality.
- Injection molding: In addition to glass aspherical lens, there are also plastic aspherical lens. Plastic molding is the injection of molten plastic into an aspherical mold. Compared with glass, plastic has poor thermal stability and compression resistance, and requires special treatment to obtain similar aspherical lenses. However, plastic aspherical lens is characterized by low cost, light weight and easy to be shaped. It is widely used in moderate optical quality, insensitive thermal stability and low pressure resistance.
Plastic shaped aspherical lens, with low cost and light weight, is suitable for manufacturing lens of large batch, moderate quality and low thermal stability.