Patent ID: 7771058

Claim:
A portable projection display apparatus comprising: a screen having a projection surface; a projection device including an image forming means for forming image light and a projection optical lens system which projects the image light, obtained by the image forming means, toward the projection surface such that the projection optical lens system is able to change a projection direction of the image light; a swinging detecting means for detecting a relative swinging of the projection device with respect to the projection surface based on an energy wave which arrives from the projection surface by passing through the projection optical lens system and does not adversely affect the image light; and a correcting means for correcting the projection direction of the projection optical lens system in accordance with an output value of the swinging detecting means, so as to cancel a relative movement of the image light in the projection direction that is caused by the swinging, wherein the swinging detecting means includes a radiation source which is stored in the projection device for emitting the energy wave and a sensor which detects the energy wave which is emitted from the radiation source, passes through the projection optical lens system, is projected on the projection surface, is reflected by the projection surface, passes through the projection optical lens system and is incident on the sensor, and the swinging detecting means detects the relative swinging of the projection device with respect to the projection surface based on the energy wave detected by the sensor, the projection surface is provided with a marking which gives a predetermined characteristic to the energy wave reflected by the projection surface based on an interaction between the marking and the energy wave, and the optical lens system is configured to be able to adjust a focus of the projected image light, the portable projection display apparatus further comprising an automatic focus adjusting means for detecting a focus status of the optical lens system based on the energy wave which is detected by the sensor of the swinging detecting means and to which the predetermined characteristic is given, and for adjusting the focus of the optical lens system based on the focus status.