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Basic principles of lens design and the role of filters
Lens design is a very creative work. It must be based on experience and keen insight to understand the characteristics of various optical aberrations.
First, let’s look at some basic principles of lens design
Any lens, whether new or old, The term 'lens description' can be used to distinguish the number of lenses, the type of glass, the radius of curvature of the lens, the thickness of the lens, the distance between the lens and the lens, and the diameter of each lens, and so on.
These are the parameters used to comprehensively describe a lens. When the light from an object passes through the glass surface, the light will be refracted, as described in the physics knowledge we learned in the middle school physics textbook.
The amount of light refraction depends on the refractive index of the glass. If the lens designer can know the exact position and angle of incidence when light enters the optical lens of the lens front lens, he can accurately trace the optical path through the ray theory system.
The angle and distance can be calculated by the sine and cosine of the trigonometric function. Therefore, through simple plane geometry, the route of the light can be traced. We know that the energy emitted by any point light source is scattered, and there is no direction to behave.
Only part of the energy passes through the lens, and the designer also assumes that the energy passing through the lens (those regarded as a series of independent rays) can be traced through simple mathematics The path of those rays.
The lens designer first starts to trace a small amount of light from a certain point on the optical axis. The assumption here is that each object image point will be formed at its corresponding point on the film plane, so the light from the object will be transformed into a phase point such as an optical lens and have the same relative position.
This is Gaussian Fiction. Corresponding to those points close to the optical axis, the designer can have reason to believe that Gaussian imaging is quite accurate, which is the parallel optical axis optics (Paraxial Optics). Although the calculation formula is quite simple (at least for experienced designers), the calculation of these numbers is required to be accurate to 5 to 8 decimal places.
Filter (protective lens) In photography, the filter (protective lens) is used to protect the lens and filter the light. The lens in the camera is the most precious. It is necessary to strengthen the protection. It is necessary to install the filter lens to prevent some dust from corroding. Of course, it is also very convenient to wipe it. Don't worry about damaging the lens. The focus lens accepts the light when the lens is shooting, just like people see the object. If you look at things under strong light, you will be uncomfortable and your eyes will be tired. So I wear filter glasses and feel that my eyes are more comfortable. That's because of the lens. Blocks a part of the strong ultraviolet rays, allowing the eyes to accept external things in a relieved situation.
The filter lens on this lens is also the same. It can effectively prevent the intrusion of strong ultraviolet rays and cause the sharpness of the image. Second, it can prevent some Air pollution corrodes the lens. When using a traditional camera to shoot with film. Due to the chemical properties of the film, it is particularly sensitive to ultraviolet rays in the sun. In places where the ultraviolet rays are strong, the photos taken with the film are generally blue and white. Seriously affect the photo quality.
Add a filter (protective lens) in front of the lens, which can effectively filter out ultraviolet rays and improve the clear aspherical degree of the photo. For high-altitude photography or high-altitude photography, you can make the distant scenery clearer and restore a more realistic and gorgeous picture.
So at that time, the filter became a necessary color filter. Because the filter can not only improve the image, but also protect the lens from dust, fingerprints and other pollution. and so. The filters are always installed in front of the lens without taking them off, making them the most widely used color filters.
In the digital age, since the core imaging component CCD of the digital machine is no longer as sensitive to ultraviolet light as the film, the filter (protective lens) has the filtering function of ultraviolet light. Was gradually faded, but damage to the lens coating still exists due to oil stains, fingerprints, and scratches. The filter at this time plays more of the role of a protective lens. Some people worry that the image quality will be affected because of the additional filter.