1. Field of the Invention
The present invention relates to an image projection apparatus, and particularly to an image projection apparatus which uses a zoom lens for projecting an image onto an image receiving plane and further relates to a method of driving a zoom lens of an image projection apparatus.
2. Description of the Prior Art
A microfilm reader-printer which projects a magnified image on a screen and copies the magnified image on a copy paper uses a zoom lens for altering magnifications of projection according to the size of original image on a microfilm and the size of the copy paper. Such a microfilm reader-printer using a zoom lens often needs to recognize the magnification of the zoom lens in order to indicate the magnification on a display numerically or alter the magnification to a specified value. To meet this requirement, the conventional microfilm reader-printer is designed such that when the zoom lens is attached to the microfilm reader-printer, an initializing operation takes place to set the magnification of the zoom lens to a reference value regardless of the current magnification of the zoom lens.
On the other hand, when the microfilm reader-printer is used in a copy operation, only a few kinds of magnifications are required in general because of the standardized dimensions of the frame of the microfilm and the copy paper. For example, in many cases, the first copy operation uses magnification A, the second copy operation uses magnification B, and the third copy operation uses the magnification A again.
It is a tedious task to set the magnification of the zoom lens to another value each time the projection condition varies, and therefore a conceivable maneuver is to prepare several zoom lenses, with magnifications for intended projection conditions being set in advance, and to select a lens which meets the projection condition. However, for the above-mentioned microfilm reader-printer in which the reference magnification is set automatically when the zoom lens is mounted, it is not possible to preset the intended magnification, and the operator is obliged unfavorably to reset the intended magnification at each operation.