Lens structure of lens

(1). Number of lenses: Multi-type lens combination can reduce color shift and improve focus, but it will reduce light transmittance.

(2) Lens transmittance: A good lens transmittance is good and expensive, while a poor lens will block light from passing through.

(3) Coating and grinding: The coating and grinding process of lenses affects the quality of lenses.

(4) Mechanical device: The accuracy of the internal mechanical structure of the lens affects the accuracy and reliability of the lens movement. Bad mechanical structure will produce adjustment errors and inconsistencies.

A simple lens composed of single or double cemented lenses

Because this simple lens is only composed of single or double cemented lenses, its aberration can not be perfectly corrected, and the aperture is very small, so it can only be used under strong light. However, due to the low price of such lenses, especially the widespread use of optical plastics (PMMA) instead of optical glass, its manufacturing cost is lower. So most toy cameras and disposable cameras on the market use this simple lens.

Two or three sets of Kirk [Cook] lenses

The early Kirk lens consists of three independent lenses, and its aperture is located between the lenses. This kind of optical structure is the simplest structure that can initially correct lens aberration, and the imaging quality basically meets the requirements of general public cameras (lens grade is 2 ~ 3), and the price is relatively low. In recent years, in order to adapt to the development of automatic cameras and pocket cameras, the aperture of the usual three-piece Kirk lens has been moved from the middle of the lens to the back of the mirror to make the lenses closely connected. Due to the asymmetry of optical power caused by the backward movement of the aperture, the system has a large off-axis spherical aberration. In order to ensure the aberration, we have to stop the light, so the edge illumination is relatively low, which needs to be considered in design and use.

In order to further reduce the cost, most low-grade parallel cameras in the market use optical plastics lens to replace one of Kirk's three objective lenses (mostly the middle one), and its relative aperture can only be about 1/4.5.

Three sets of [Tessar] four-piece photographic lenses

As shown in figure 1-2- 18, the Tiansai lens developed by Kirk, 1902 originated from Zeiss Optical Factory in Germany and was first designed by the famous optical expert Lu Dollof. It uses a double cemented lens group to replace the third lens of Kirk lens, so the relative aperture of the lens can be greatly improved, and its relative aperture can reach 1/3.5 ~ 1/2.8 under the condition of medium field of view of 50 ~ 60. At present, it is the most widely used lens structure form for mid-range or mass cameras in China. The aperture is located between the second group and the third group, forming a positive power photographic objective lens with asymmetric structure.

The introduced cemented lens group fully improves the astigmatism and off-axis of the objective lens, so it is especially suitable for landscape photography.

Four, double Gaussian objective lens and its evolution form

The double Gaussian objective lens is an objective lens with a large field of view (about 40), and its relative aperture first reaches F/2. The original design is shown in figure 1-2- 19. Adding two glued surfaces makes it possible to better eliminate aberrations. Although the dispersion of the glass on both sides of the bonding surface is different, the refractive index is almost the same, so the addition of the bonding surface has little effect on the monochromatic aberration. The basic symmetrical structure is conducive to the correction of coma, distortion, magnification chromatic aberration and other vertical aberrations. There are two strong concave lenses on both sides of the aperture, which is conducive to the correction of spherical aberration and astigmatism. The complex type of double Gaussian objective lens mainly increases the relative aperture of the lens or improves the imaging quality of the lens. The most common method is to replace the front or rear positive lens with two single positive lenses, as shown in figure 1-2- 19(a). It can reduce the off-axis goal difference of the field of view and the on-axis goal difference of the aperture at the same time, and can obtain higher imaging quality under the condition of larger field of view.

Another complex form of double Gaussian objective lens is to replace the adhesive surface in the front and rear thick lenses with the separation surface; Or split the front or rear positive lens into two at the same time.