Recently, because of spread of a DVD or starting of digital high-vision broadcast, environment for entertaining high image quality video contents at home has been prepared. Therefore, large displays are rapidly in increasing demand. In particular, a projection display apparatus represented by a liquid crystal projector is more inexpensive and has a larger display size than other systems such as a plasma display panel (PDP), so that a user can enjoy video. Accordingly, this projection display apparatus has come into wide use as a home theater system. To obtain high image quality of the projection display apparatus, a method for performing high dynamic ranges by controlling amount of light of a lamp in response to brightness of the image is invented (See for example, Unexamined Japanese Patent Publication No. 2001-100699).
FIG. 13 is a top view showing an optical layout of a conventional liquid crystal projector.
Light emitted from lamp 150 of a light source is divided into a plurality of partial luminous fluxes by first lens array 151, and enters into polarization change element 153 via second lens array 152. Each partial luminous flux is made its polarization direction arranged, and becomes linear polarization. Then it is transmitted through diaphragm mechanism 165, and enters superimpose lens 154.
Dichroic mirror 156R reflects only red light, and lets other light pass. Dichroic mirror 156G reflects only green light, and lets other light pass.
Among light emitted from superimpose lens 154, red light “R” is reflected and separated at dichroic mirror 156R. Among light transmitted through dichroic mirror 156R, green light “G” is reflected and separated at dichroic mirror 156G, so that blue light “B” is transmitted.
Red light is reflected at total reflection mirror 157R, transmitted through field lens 159R and reaches liquid crystal panel 155R.
Green light “G” is transmitted through field lens 159G and reaches liquid crystal panel 155G.
Blue light “B” is transmitted through relay lens 158Ba, reflected at total reflection mirror 157Ba and transmitted through relay lens 158Bb. After that, blue light “B” is reflected at total reflection mirror 157Bb, transmitted through field lens 159B and reaches liquid crystal panel 155B. Liquid crystal panels 155R, 155G and 155B work as a kind of optical modulators.
Three color lights transmitted through liquid crystal panels 155R, 155G and 155B are superimposed at cross prism 160, and projected via projection lens 161.
Arrow 162 denotes a direction in which the superimposed light is projected.
FIG. 14 shows general diaphragm mechanism 165.
A luminous flux emitted from the lamp passes through part 168 where the luminous flux passes, and passes through opening 167 formed by diaphragm blade 166.
Diaphragm mechanism 165 is formed of a plurality of diaphragm blades 166, and an amount of light of lamp 150 is controlled by changing an area of opening 167 continuously using driving means such as a motor (not shown). A motor is driven in synchronization with brightness of an image in such a manner that the area of opening 167 becomes large when the image is bright and the area of opening 167 becomes small when the image is dark. Thus, high dynamic ranges can be performed.
The conventional projection display apparatus discussed above needs a space for storing the diaphragm blades. The space is larger than a section up which a luminous flux from the lamp takes, thereby making the apparatus difficult in downsizing. In addition, because many diaphragm blades are needed, components increase in number, so that the apparatus tends to be expensive. A phase plate or a polarizing plate can be utilized instead of the diaphragm blade, however, it is also expensive, so that it is not practical.
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USPTO Backgrounds