1. Technical Field
The present disclosure relates to an imaging apparatus.
2. Description of Related Art
An imaging apparatus generally includes a number of lenses and an imaging sensor. The imaging apparatus focuses by changing the distance between the lenses. Referring to
However, with the above configuration, because the first lens 11 is the outermost lens, when it is moved back and forth in the barrel, it first exposes portions of the barrel, which can collect dust, then encloses those portions so that the dust may penetrate the imaging apparatus. To avoid this, the second lens 12 could be moved instead of the first lens 11, however, movement directions of the lens 12 would be different than the lens 11 and require redesign of the driving device 17 which is difficult and costly.
What is needed therefore, is an imaging apparatus which can overcome the above-mentioned problems.
The components of the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments of the imaging apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the views.
Referring to
The four lenses 21, 22, 23, 24 can be made of plastic, to reduce costs, and all have opposite aspherical surfaces (i.e., the aspherical object-side surface and the aspherical image-side surface) to efficiently correct aberration. The aspherical surface is shaped according to the formula:
where h represents a height from the optical axis of the imaging apparatus 100 to the aspherical surface, c represents a vertex curvature of the aspherical surface, k represents a conic constant, and Ai represents i-th order correction coefficients of the aspherical surfaces. In this embodiment, i is consecutively selected as 2, 4, 6, 8, 10, 12, 14, 16.
Table 1 shows the parameters of the surfaces S1-S11 of the imaging apparatus 100. Wherein the parameters: R is the curvature radius of the surface, T is the thickness from the vertex of the surface to the center of the lens, D is the diameter of the surface, c is the vertex curvature of the surface.
Table 2 shows the correction coefficients of the aspherical surfaces S1-S11.
The imaging apparatus 100 changes the focusing position by moving the second lens 22. In general, the imaging apparatus 100 is at a general infinite focus setting, the second lens 22 is moved to the object side when changing the focus setting of the imaging apparatus 100 from the general infinite focus setting to the close-up focus setting. The movement direction of second lens 21 from the general infinite focus setting to the close-up focus setting is the same as the direction the first lens 11 of
In this embodiment, light with the wavelength of 656.3 nanometers (nm), 587.6 nm, 546.1 nm and 436.0 nm are selected for testing the optical characteristics of the imaging apparatus. The refractive indexes of the lenses 21, 22, 23, 24 and the IR filter 25 are greater than 1.5. Table 3 shows the detailed refractive indexes of lenses 21, 22, 23, 24 and the IR filter 25 in response to different wavelengths of light.
The imaging apparatus can focus at a close-up focus setting as 100 mm. In this embodiment, focusing at 130 mm is selected as the close-up focus setting.
As illustrated in
In
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure.
Number | Date | Country | Kind |
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200910312385.4 | Dec 2009 | CN | national |