1. Camera Lenses
The optical property can be represented by three parameters, which are the focal length f’, the relative aperture D/f’ and the field angle 2ω'. As for the camera 135, its standard size of picture is intended to be 24mm X 36mm. Therefore, its diagonal is 2D=43.266. According to the following list, we can conclude the formula between focal length and field aperture: tgω'=D/f'.
In the formula: 2D——the length of its diagonal
f‘——the focal length of lenses
Another essential optical characteristic of camera lens is the relative aperture. Relative aperture means the transmission ability of lenses, representing with D/f’. The aperture coefficient is also called F-number. F=f’/D.When f’ is fixed, the F-number grows in inverse proportion to the diameter D. Since the square of D is proportional to the light area, the bigger the area is, the bigger is the amount of passed light. Therefore, when the F-number is at the smallest amount, the unthreaded hole is at the biggest size, and the amount of passed light too. With the increase of the number of aperture, the aperture will get smaller, the luminous flux is also reduced. If the difference of the amount of light which pass through the lenses is not considered, no matter how long the focal length is, and no matter how big the diameter of the light hole is, as long as the F-numbers are fixed, their flux are the same. F-number is a particularly important parameter for a camera lens, the smaller the number is, the wider its arrange of application can be. Compared with the visual optical system, and camera lens also has large relative aperture and large field of view. Therefore, in order to make the image be seen clearly which is similar to the physical object, almost all the seven aberrations should be corrected. The resolution ratio of the photographic lens is a comprehensive reflection of the relative aperture and aberration. After the relative aperture is confirmed, to establish a required correction scheme which is easy to achieve, the dispersion circle radius is often used to measure the size of the aberration, and finally, the optical transfer function is used to evaluate the image quality.
The attributes and design evaluations of those recently rised digital camera lenses are similar to the above mentioned lenses. The main differences are:
1. The relative aperture is bigger than traditional cameras.
2. The short focal length makes the field look deeper. The focal length can be calculated through the size of field angle: F’=43.266/（2*tgω）.
3. High resolution ratio. According to the size of the PIXEL of optoelectronic devices, general digital optical design should achieve 1/ (2*PIXEL).
2. Projection Lenses
Projection lenses projects the object lightly and clearly to the screen. The image distance is generally bigger than the focal length, therefore the object plane is near the outside of the focal plane .
The magnification of projection lenses is an important parameter when measuring the accuracy, size of aperture, observation arrange and structure size.
The bigger the magnification is, the better the measurement accuracy will be, the bigger the size of the aperture can be. When the working distance is fixed, the further is the conjugate distance, the larger the structure size of the projection system will be. Since its function is to amplify, we can learn from optical knowledge that the illumination of the center of the image is proportional to the square of the relative aperture, and it can be lightened by increasing the relative aperture.
Compared with traditional projection lenses, the differences of the projection lenses used on the LCD projector are:
1. Big relative aperture
2. Long distance of exit pupil, which means it should be designed to telecentric light path.
3. Long working distance
4. High resolution
5. High demand of distortion
All above have made the projection lens used for LCD projector more complex compared with the traditional projection lenses. Generally it needs10 lenses, while traditionally 3 lenses are enough to project.
3. Scanning Lenses
Scanning lenses can be represented with three optical properties——relative aperture, magnification and conjugate distance. Magnification is an essential indicator of scanning lenses. Because the size of common objects are fixed, the smaller the magnification is, the smaller the image in the lens will be, and the shorter the focal length will be.Relatively speaking, the structure of scanning system can be made smaller, but the resolution is also demanded to be higher. The conjugate distance refer to the distance between objective images. The lens is commonly desired to be long. The shorter the conjugate distance is, the harder it will be to design the lens. Its schematic diagram is the same as camera Lens which is the process of reduction.
The design features of scanning lenses:
1. Scanning lenses are system with small aperture and aberration, which need high optical resolution.
2. Since it is photoelectric device, not only the aberration of white light should be corrected, but also three independent waves should be considered.
3. Strict correction of distortion differences.
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