2021/06/08

1. Camera lens

The optical characteristics of a camera lens can be represented by three parameters, namely the focal length f', relative aperture D/f' and field of view of the camera lens Angle 2ω'. In fact, for the 135

camera, its standard format has been determined to be 24mmX36mm, and its diagonal length is 2Du003d43.266. From the following table, we can conclude that the following relationship exists between the focal length f'of the camera lens and the angle of view ω':

tgω'u003dD/f' where: 2D-the diagonal length of the frame; f'-the focal length of the lens.

The other most important optical characteristic index of a camera lens is the relative aperture. It expresses the ability of the lens to pass light, expressed by D/f'. It is defined as the ratio of the aperture diameter of the lens (also called entrance pupil diameter) D to the focal length f'of the lens and the reciprocal of the relative aperture is called the lens's aperture coefficient or number of apertures, also known as the F number, that is, Fu003df'/D. When the focal length f'is fixed, F

The number of is inversely proportional to the entrance pupil diameter D. Since the light-passing area is proportional to the square of D, the larger the light-passing area, the greater the luminous flux that the lens can pass through. Therefore, when the number of apertures is at the minimum, the aperture is the largest and the luminous flux is also the largest. As the number of apertures increases, the aperture becomes smaller and the luminous flux also decreases.

If you don’t consider the difference in transmittance of various lenses, no matter how long the focal length of the lens is, and regardless of the aperture diameter of the lens, as long as the aperture value is the same, Their luminous flux is the same as the lens design. For camera lenses, the F number is a particularly important parameter. The smaller the F number, the wider the scope of application of the lens.

Compared with the visual optical system, the photographic objective lens has a large relative aperture and a large field of view at the same time. For images with similar planes, almost all seven aberrations have to be corrected. The resolution of a photographic objective is a comprehensive reflection of the relative aperture and the residual amount of aberration. After the relative aperture is determined, formulate an optimal aberration correction scheme that not only meets the requirements of use, but is also easy to implement. For convenience, the 'radius of the circle of confusion' is often used to measure the size of aberrations, and finally the optical transfer function is used to evaluate the image quality.

Second, projection lens

The projection objective is to transform the illuminated object into a bright and clear real image on the screen, generally In other words, the image distance is much larger than the focal length, so the object plane is near the outside focal plane of the projection objective. The magnification of the projection objective is an important parameter of measurement accuracy, aperture size, observation range and structure size. The greater the magnification, the higher the measurement accuracy and the larger the aperture of the objective lens. When the working distance is constant, the larger the magnification and the larger the conjugate distance, the larger the structure size of the projection system. Since it plays a magnifying role, it can be known from optical knowledge that the illuminance at the center of the image surface is proportional to the square of the relative aperture. The method of increasing the relative aperture can be used to increase the illuminance of the image surface. The difference between the projection lens used on the LCD projector and the traditional projection objective:

1. The relative aperture of the optical lens is larger.

2. The exit pupil is long, that is, it needs to be designed as a near-to-telecentric optical path.

3. Long working distance.

4. High resolution.

Tips about shift lens:

1) The image captured by the image sensor of the digital SLR camera In fact, it's just the rectangular cropped part of the center area of u200bu200bthe lens image circle. The so-called imaging circle is the circular range that can be imaged by light passing through the lens, and its diameter is greater than the diagonal length of the image sensor. The image circle of the shift lens is larger than that of the ordinary lens. In this way, even if you perform tilt and deflection operations, you can ensure that the picture is within the imaging circle.

2) The tilt-shift lens is very suitable for panoramic photography and can combine multiple photos together. Unlike traditional lenses, the advantage of a shift lens is that it does not need to move the center point of the lens, thus avoiding the parallax of the foreground subject.

Under normal circumstances, the lens plane and the camera's imaging plane are parallel, and the subject plane and the lens plane and imaging plane are also parallel. If a flat object, such as a surface of a building, is also parallel to the imaging plane, then the entire object can be clearly recorded. However, if the plane of the subject is not parallel to the imaging plane, the range of clarity is limited. When the extension line is drawn through the subject plane, imaging plane and lens plane, the three lines meet at one point, that is, when the three surfaces intersect in a straight line, the scene from near to far can be clearly imaged, even when the aperture is fully opened. in this way.

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