The most significant advantage brought by the aspheric lens is that it can correct spherical aberration. Spherical aberration is produced by using a spherical surface to focus or align light. Therefore, in other words, all spherical surfaces, regardless of whether there are any measurement errors and manufacturing errors, will have spherical aberration. Therefore, they will need a non-spherical or aspherical surface to correct it.
By adjusting the conic constant and aspheric coefficient, any aspheric lens can be optimized to Minimize aberrations. For example, it shows a spherical lens with significant spherical aberration, and an aspheric lens with almost no spherical aberration. The spherical aberration in the spherical lens will cause the light incident on the optical lens to focus on many different fixed points, resulting in a blurred image; and in an aspheric lens, all different light rays will be focused on the same fixed point, so compared with The language produces less blurry and better quality images.
In order to better understand the difference in focusing performance between aspheric lens and spherical lens, please refer to a quantitative example, in which we will observe two diameters of 25mm and focal length of 25mm The equal lens (f/1 lens). The following table compares the spot or blur size produced by parallel, monochromatic light (wavelength 587.6nm) on-axis (0° object angle) and off-axis (0.5° and 1.0° object angle). The spot size of an aspheric lens is several orders of magnitude smaller than that of a spherical lens.
The performance benefits of additional optical lenses
Although there are many on the market There are many different technologies to correct the aberrations caused by the spherical surface, but these other technologies are far less than what an aspheric lens can provide in terms of imaging performance and flexibility. Another widely used technique involves increasing f/# by 'shrinking' the lens. Although doing so can improve the quality of the image, it will also reduce the luminous flux in the system. Therefore, there is a trade-off between the two.
On the other hand, when an aspheric lens is used, its additional aberration correction supports users in achieving high luminous flux (low f/#, high numerical aperture) At the same time, the system design still maintains good image quality. The image degradation caused by the higher luminous flux design of the focusing lens is sustainable, because the performance provided by a slightly reduced image quality is still higher than that of a spherical system.
place the lens in a publicity material with gravel (regulation The grain size and hardness of the gravel) are rubbed back and forth under certain control. After the end, use a haze meter to test the amount of diffuse reflection of the lens before and after friction, and compare it with the standard lens.
The relationship between anti-reflection coating and anti-wear coating
The anti-reflection coating on the surface of the lens is a very thin Inorganic metal oxide materials (thickness less than 1 micron), hard and brittle.
When it is plated on a glass lens, since the base is relatively hard and the grit is scratched on it, the film layer is relatively less prone to scratches on the aspheric mirror; but the anti-reflection film When it is plated on an organic lens, since the base is relatively soft, the grit is scratched on the film, and the film is easily scratched.
Steel wool test
Use a specified steel wool, under a certain pressure and speed, on the surface of the lens Measure the number of times of rubbing one Hun, and then use a haze meter to test the amount of diffuse reflection of the lens before and after rubbing, and compare it with the standard lens.
Of course, we can also do it manually, rub the two lenses with the same pressure the same number of times, and then observe and compare with the naked eye.
The results of the above two test methods are relatively close to the clinical results of long-term wearers. Therefore, the organic lens must be coated with an anti-wear film before the anti-reflection film is coated, and the hardness of the two film layers must match.