Improving appearance points lenses

 

Vysokoprelomlyayuschie lenses made of organic materials can significantly improve the appearance of spectacles. Using the lenses of materials with refractive indices from 1.60 to 1.74 can substantially reduce the thickness and weight of lenses and glasses to make a superficially more attractive, even at high degrees of ametropia. Variety vysokoprelomlyayuschih range of lenses in combination with optical coatings, which offer today, many manufacturers, often puts consumers in a quandary: what lens to choose? To make the right decision, we must understand the basic characteristics and features of the lens material with high and superhigh refractive index.

 

Index of refraction

This characteristic shows the relationship between the speed of light in vacuum and the speed of its spread in this material. Obtained by dividing these two parameters, the number (eg, 1,5, 1,6, 1,67, 1,74) and is the refractive index (nd). The larger the numerical value, the greater the slowing down or rejected in the material world. This means that organic materials vysokoprelomlyayuschie reject transmitted light at large angles than the standard plastic with nd = 1,50, and hence the lenses of these materials requires less curvature of the surface to ensure the same optical power as in a standard plastic lenses. Thus, the lens of material with nd = 1,67 will be much thinner than a standard lens with organic nd = 1,50 the same refraction.

Vysokoprelomlyayuschie lenses have a flat surface than a standard plastic lens, and the combination with aspherical design has further thinning and flattening of the lenses of both positive and negative refraction. Such lenses are well suited for assembly in the popular frame of small geometric dimensions with a low angle of the bend. At the same time to build the adjacent frames with a higher surface curvature is necessary to use a special lens design that have already appeared in the range of producers. Several vysokoprelomlyayuschih materials, such as nd = 1,67, characterized by high physical and mechanical characteristics, which makes the lenses based on them suitable for assembly in eyeglasses with lens mount with screws.

Abbe Number

If you look at vysokoprelomlyayuschuyu not through the lens optical center, and through a remote area of it, it will become visible color components making up the white light radiation. These components are distributed differently, depending on the wavelength, which can lead to a deterioration in the quality image of the object as seen through the lens. This effect is called chromatic aberration, and from time to time, users complain of her points (describing the halo or colored rim around the edges of the object). The main task of the developers of lenses is to minimize chromatic aberration.

The quantitative parameter used to determine the chromatic aberration of the optical material, called the Abbe number. The lower the value of this number (see table), the more noticeable chromatic aberration, and the greater its value means that reduction.

In the optical center of lens chromatic aberration of the least visible and well-tolerated. Its effect may also be reduced by minimizing the lens decentration and the use of frames with the small size of optical apertures. During the assembly points should strive to ensure that the optical center with the best optical properties are located directly opposite the pupil, and try to reduce those areas of the lens, in which the effect of the expansion of colors more visible.

The properties of antireflection coatings

Physical methods completely eliminate the phenomenon of chromatic aberration does not exist, but according to experts, drawing anti-reflective coatings improves the portability of glass lenses with small values of the Abbe *, and is mandatory for lenses from vysokoprelomlyayuschih materials. After all, these lenses have a more compact structure and reflect more light than traditional lenses of materials with nd = 1,50. The higher the number of reflected light from both surfaces causes the formation of interfering light, even under normal lighting conditions and creates an annoying ghosting when there are multiple light sources or made sources of bright light in a relatively dark environment (candles in the darkened restaurant, the lights of the oncoming car while driving in the dark days, etc.). Application of high-quality anti-reflective coatings can dramatically reduce the amount of reflected light and provides improved optical lenses and of their appearance.

Protection from ultraviolet

Chemical structure vysokoprelomlyayuschih lenses helps cut damaging ultraviolet (UV) radiation, while the standard plastic lenses require special methods of modification, such as printing UV-absorbing coating or treatment in a solution of UV-absorbers, which can lead to a visually appreciable yellowing.

We do not recommend vysokoprelomlyayuschie lens

As sales grow lenses of materials with high refractive index, some experts in the field of optical correction of vision expressed the view that designate these lenses should not everyone. Consider the case where the choice vysokoprelomlyayuschih lenses are not recommended .**

* You ametropia less than 2.5 diopter. In this case, it is difficult to notice and appreciate such advantages vysokoprelomlyayuschih lenses, the smaller weight and thickness, especially when building a frame with small sizes of skylights. At the same time, the choice of an aspherical lens and atoricheskogo designs for small refractions can be fully justified, since these designs offer significant optical advantages by reducing the astigmatic error in the peripheral zones of lenses.
* Select Points bezobodkovoy design. Care should be taken when performing such an order at a complete set of his vysokoprelomlyayuschimi lenses. If a company - the manufacturer of lenses does not mention that vysokoprelomlyayuschy material data elements recommended for bezobodkovyh points, it is better to opt for the lens of polycarbonate or trayveksa that have high impact resistance.
* In translating look you prefer roll their eyes, not the head. These customers will be more sensitive to the appearance of chromatic aberration when you look through the peripheral zone lenses. Fortunately, people with a high degree of refractive error, and which are most suitable candidates for appointment vysokoprelomlyayuschih lenses typically refer to those when examining an object rotates more head .***
* Build in a frame of different lenses. When working with vysokoprelomlyayuschimi lens assembly in a single frame of lenses with different values of the refractive index is unacceptable, even if you follow the intentions lining thickness ordered lenses with refractive error and therefore are looking for a lens with a smaller force of the optical material with nd = 1,50, and for a lens larger refractive - with nd = 1,60. In such glasses the client will feel discomfort.
* Adjacent-frame. High curvature inherent in these frames, difficult to reconcile with the more flat surfaces vysokoprelomlyayuschih lenses, and the result will have a ready-made spectacles unaesthetic appearance.