| dc.description.abstract | This thesis proposes a periscope-type zoom lens optical design which can be embedded in the mobile phone. In order to avoid the lens of mobile phone protrude from the casing, the lens depth of zoom lens must be less than the thickness of the mobile phone mechanism. Refer to the size of iPhone, the casing of mobile phone mechanism is about 3 mm, and the thickness is 5 mm without the casing of mobile phone mechanism.
The optical axis of object light will reflect by the prism and pass through the lens module and the lens depth is defined as the upper size limit of the prism thickness or the maximum surface aperture in the Y-direction of the zoom lens. The lens depth is related to the length of the sensor in the Y-direction, the entrance pupil diameter, the entrance pupil position, and the angle of view in the Y-direction. When the lens depth of zoom lens is less than the thickness of mobile phone mechanism, it can be embedded in the mobile phone.
The design specifications of this thesis include the effective focal length from 3.27 mm to 1.64 mm, the half field angle from 29 to 5.28, the F/# from 3.4 to 6.8, and the entrance pupil diameter from 0.96 mm to 2.89 mm.
In order to reduce the field angle in the Y-direction of incident light and lens aperture, we can reduce the length in the Y-direction of sensor by changing the ratio of sensor from 4:3 to 16:9, but keeping the diagonal height. When doing the lens design, we can adjust the maximum effective lens aperture by controlling the distance of entrance pupil, the longer the distance, the larger the lens aperture.
Because the sensor is rectangular type, we can define the maximum lens aperture of all the lenses by doing the real ray tracing, it is one of function in the CodeV. We can cut the ineffective part of every lens in the lens module, the shape of lenses will change form circle to square, it will make the result of lens design simpler to put into the smaller mobile phone.
In summary, we choose 5 mega pixels instead 8 mega pixels of sensor. It’s hard to reach our design target by using 8 mega pixels of sensor, because the more pixels, the field angle and lens depth are bigger. We improve the ratio of sensor dimension from 4:3 to 16:9, so, we could get smaller field angle in Y-direction. We also consider about the finite lens depth will need more lenses and aspherical lens to meet our optical performance design target when doing the higher zoom ratio design, therefore, we choose 6 zoom ratio as our design target. Finally, the design result of the lens depth is 4.98 mm, and the total length of zoom lens is 31.9 mm, so, it can be embedded in the mobile phone.
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