A projecting device, particularly for use in photogrammetry, employs a Fresnel condensor for illuminating a picture carrier which is imaged through an objective, including a diaphragm, onto a projection table. At least half of the illumination rays entering said objective, is suppressed by said diaphragm. The Fresnel condensor and the severe stopping-down of the objective produce interfering chromatical effects on the projection table. Said chromatical effects are eliminated either by means of a bi- or multifocal embodiment of the Fresnel lens or by insertion of optical means which extend the optical illumination path or by a respective embodiment of the light source.
Apparatus is disclosed which functions with a scanning arrangement including a charge coupled device (CCD) scanner and an analog-to-digital converter to digitize documents for storage, display and transmission to a remote location. The apparatus is attached to the scanner and consists of a reticle with a site pattern thereon, a lens arrangement and a lamp which are used to position a document for scanning. Prior to scanning the document the lamp is briefly energized to project the pattern onto an easel on which the document is placed, and the portion of the document on which the pattern is projected is the portion that will subsequently be scanned by the scanner.
A Fresnel lens sheet of a multifocal type is intended to be used in combination with a lenticular lens sheet to construct a rear projection screen for a rear projection television receiver. An annular portion (2) of the Fresnel lens sheet at a distance (R) in a range of 0.05 h to 0.5 h, where h is the height of the Fresnel lens sheet, from the optical center (C) of the Fresnel lens sheet, have the shortest focal length f.sub.min among those of other portions of the Fresnel lens sheet, whereby uniformity in brightness of a screen employing the Fresnel lens sheet can be achieved. Alternatively, a portion where an exit angle (.theta.) of outgoing light ray relative to a normal to the surface of the Fresnel lens sheet is the greatest, lies at a distance (R) in a range of 0.3 h to 0.8 h from the optical center (C) of the Fresnel lens sheet, to obtain the same result.
In a liquid crystal projector wherein a light source is arranged behind a transmission liquid crystal display panel having a rectangular display portion, an image displayed on the liquid crystal display panel is enlarged by a projection lens, and an enlarged image is projected on the screen located in front of the liquid crystal display panel, a linear Fresnel lens is arranged between the light source and the liquid crystal display panel to narrow illumination light beam from the light source along only the widthwise direction of the rectangular display portion. When the illumination light beam from the light source is narrowed along only the widthwise direction of panel, the amount of unused light beam emitted outside the long sides of the display portion can be reduced, and the light beam from the light source can be effectively utilized for image projection.
A projection-type liquid-crystal display in which a Fresnel lens in placed on the exit side of the liquid crystal panel to focus the image toward a projection lens. Preferably, the Fresnel lens has a non-symmetric pattern so as to efficiently gather light propagating through the display panel at an oblique angle coinciding with a reorientation angle of the liquid crystal. Additional optics on the incident side of the panel, perhaps including another non-symmetric Fresnel lens, collimates the light at the oblique angle.
