Lens module and camera employing the same

A lens module includes a barrel defining a through hole, at least one plastic lens accommodated in the through hole and a UV/IR cut filter mounted on the barrel and configured for preventing entry of both UV light and IR light into the barrel. The lens module has a UV/IR cut filter mounted on the barrel configured for preventing entry of both UV light and IR light into the barrel, so it can prevent UV light damaging plastic lenses, and accordingly can improve the useful life of the lens module.

BACKGROUND

1. Field of the Invention

The present invention relates to lens modules and cameras and, more particularly, to a lens module that can prevent a plastic lens therein from being affected by ultraviolet light, and a camera employing the lens module.

2. Description of Related Art

Generally, image pick-up devices such as charge coupled devices (CCD) or complementary metal oxide semiconductors (CMOS) used in, for example, cameras, react to light even in the near-infrared region beginning at a wavelength of about 700 nm and in the infrared (IR) region. However, light in the near-infrared and IR regions causes crosstalk that reduces a signal-to-noise ratio of an image pick-up device and thereby deteriorating the device's reproduction ability. In order to prevent such reaction and crosstalk, IR cut filters that block light in the near-infrared and IR regions are assembled in lens modules implemented in conventional cameras.

However, in a conventional lens module, the IR cut filter usually is assembled as the last part for the lens module by using ultraviolet (UV) glue on a spacer. The use of UV glue has adhesion and reliability problems. Also, a plastic lens in the lens module may be affected by UV light in sunlight, or by UV light used in UV curing processes. Many plastic lenses turn yellow with long-term exposure to UV light.

What is needed, therefore, is a lens module which can prevent plastic lenses from being affected by UV light.

SUMMARY OF INVENTION

In accordance with one embodiment, a lens module includes a barrel defining a through hole, at least one plastic lens accommodated in the through hole and a UV/IR cut filter mounted on the barrel and configured (i.e., structured and arranged) for preventing entry of both UV light and IR light into the barrel.

In accordance with an embodiment, a camera includes a lens module and an imaging module. The lens module includes a barrel defining a through hole, at least one plastic lens accommodated in the through hole and a UV/IR cut filter mounted on the barrel and configured for preventing entry of both UV light and IR light into the barrel. The imaging module is coupled to the lens module, and includes a holder and an image sensor received in the holder.

Other advantages and novel features will become more apparent from the following detailed description of present lens module and camera, when taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION

Embodiments of the present lens module and camera employing the lens module will now be described in detail below and with reference to the drawing.

Referring toFIG. 1, a camera100according to an embodiment includes a lens module20and an imaging module40coupled to the lens module20. The imaging module40includes a holder30and an image sensor10received in the holder30.

The image sensor10is configured for connecting to a circuit board and can convert optical signals to image signals. The image sensor10can be a CCD or a CMOS. Preferably, the image sensor10is packaged in a ceramic leaded chip carrier (CLCC), plastic laded chip carrier (PLCC) or chip scale package (CSP). A glass cover11is disposed on the top of image sensor10in order to avoid contamination.

The lens module20is coupled to the imaging module40. In order that a distance between the lens module20and the image sensor10received in the holder30can be changed for focusing, preferably, the lens module20is engaged with the holder30by cam structure or thread structure. In present embodiment, the lens module20is threadedly engaged with the holder30.

The lens module20includes a barrel21defining a through hole211, at least one lens group22accommodated in the through hole211and a UV/IR cut filter23mounted on the barrel21.

The barrel21can be made of a material selected from the group consisting of polycarbonate, acrylonitrile-butadiene-styrene, and any combinations thereof. The barrel21can also have a focus adjusting ring212arranged at one end thereof with the UV/IR cut filter23mounted thereon. Preferably, the focus adjusting ring212is integrally formed with the barrel21.

In present embodiment, the lens module20only has one lens group22. In order from the object side, the lens group22includes a first lens221and a second lens222with same optical axis. At least one of the first lens221and the second lens222is a plastic lens. The first lens221has a peripheral annular wall2211defining a cavity2212, so that the second lens222can be inserted inside the cavity2212and surrounded by the peripheral annular wall2211to achieve a close-fit with the first lens221. Both the first lens221and the second lens222have anti-reflection coatings coated on the two surfaces intersecting with the optical axis. Preferably, the anti-reflection coating has transmittance more than 92% for the wavelength from 400 nm to 700 nm. A first spacer223is arranged between the first lens221and the second lens222and a second spacer224is arranged between the second lens222and the barrel21. Both the first spacer223and the second spacer224are made of dark polymer material to avoid multi-reflection, flare, and ghost images.

The UV/IR cut filter23configured for preventing entry of both UV light and IR light into the barrel21and damaging plastic lens and image sensor10. The UV/IR cut filter23includes a UV/IR cut filter film232and a transparent board231with a first surface2311and an opposite second surface2312. The UV/IR cut filter film232can be formed on one of the first surface2311and the second surface2312or on both the first surface2311and the second surface2312. In present embodiment, the transparent board231is a glass board with the UV/IR cut filter film232formed on the first surface2311and an anti-reflection coating233on the second surface2312to ensure the transmittance of approximately more than 92% of incident visible light. Preferably the UV/IR cut filter23should allow transmittance of visible light in an approximate range from 95% to 99.8%.

The UV/IR cut filter film232is a film stack. The film stack includes a plurality of high refractive index layers and a plurality of low refractive index layers alternately stacked one on another, wherein the film stack is represented as follows:
(3.5H3.5L)7(2.5H2.5L)7(HL)6(0.76H0.76L)6
wherein H represents a high refractive index layer having a base optical thickness equal to one fourth of a reference wavelength associated with the filter, L represents a low refractive index layer having a base optical thickness equal to one fourth of a reference wavelength associated with the filter, the expression enclosed in each parenthesis represents a filter cavity, and the superscript represents the number of repetitions of the expression enclosed in that parenthesis. The high refractive index material has a refractive index in an approximate range from 2.0 to 2.3 and can selected from a group consisting of Ti3O5, TiO3, TiO2, Ta2O5, and any mixtures thereof. The low refractive index material has a refractive index in an approximate range from 1.4 to 1.6 and can selected from a group consisting of SiO2, Al2O3, AlN, and any mixtures thereof. In present embodiment, the high refractive index material is TiO2and the low refractive index material is SiO2. Preferably, the UV/IR cut filter film232has a transmittance of UV light with wavelength in an approximate range from 200 nm to 350 nm less than 1% and a transmittance of IR light with wavelength in an approximate range from 700 nm to 1100 nm less than 1%.

As stated above, the lens module and the camera employing the lens module have a UV/IR cut filter mounted on the barrel and configured for preventing entry of both UV light and IR light into the barrel and thus prevents UV light damage to plastic lenses, and accordingly, can improve the use life of the lens module and the camera employing the lens module.

It is understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiment without departing from the spirit of the invention. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.