Soft focus

Abstract: A projection arrangement for projecting three-dimensional images of objects into space. The object is illuminated by a source of light, and the light rays reflected from the object are directed so as to be incident on a mirror surface located behind a lens. The mirror surface receives an image from the lens and the combination forms an enlarged three-dimensional image projected into space. The lens can be in the form of a modified Fresnel lens of multiple focal lengths and having spherical zones in the form of strips. The Fresnel lens, which may be used in combination with other optical elements, provides a substantially large field of view suitable for viewing a three-dimensional image of the object by a mass audience. The image projection may be achieved without the use of a screen. The enlarged three-dimensional image appears floating in space visible to unaided eyes of an audience.

Abstract: This paper presents a simple and inexpensive multiview 3D display system composed of a LCD panel, a convex lens array, and a Fresnel lens. In the proposed system a pair of the LCD fragment and a convex lens in the array plays the role of a projector. The idea of multiview 3D displays composed of multiple projectors and a large convex lens or a concave mirror is old and famous. The conventional methods, however, require diffusers to show continuous motion parallax, which decays the quality of the image. To solve this problem we use a convex lens array with no gaps between the lenses, which realizes continuous motion parallax without diffusers. The convex lens array, however, has to produce images without aberration to show the viewer stable 3D images. It is hard and expensive to realize such lens arrays without gaps between the component lenses. To produce images with little aberration in a simple format, the author proposes the optical system where each component lens makes the parallel light rays instead of creating an image by keeping the distance between the LCD surface and the lens array the same as the focal distance of the component lenses. To create an image, we use a large convex-type Fresnel lens, which has been used only for the purpose of distributing multiview images to each viewpoint in the conventional multi-projection systems. Fresnel lens, receiving parallel light from the lens array, creates a floating real image at its focal distance and attains distribution of multiview images at the same time. With this configuration we can create images with little aberration even when we use a lens array composed of simple convex-type Fresnel lenses widely available with low prices.

Abstract: It is, of course, well known that if we focus a camera on an object at some definite distance from the camera lens, there will be a finite range of distances in front of and beyond the focused object in which everything appears acceptably in focus, while outside that range everything becomes progressively more blurred at increasing distances from the plane of best focus. The actual extent of this range of acceptably sharp definition depends mainly on the distance of the subject from the lens, the aperture of the lens, and on the manner in which we look at the final print, but it also depends to some extent on the type of subject being photographed, the resolving power of the film and paper emulsions, and the aberrations of the camera lens. However, for the sake of simplicity, the following discussion will be based on the assumption that we are using grainless film and aberration-free lenses, and we shall end with a few remarks on the effects of these neglected factors in actual practice. For ordinary fairly distant objects, the depth of field of most cameras is generally adequate, provided that we take care to focus the lens on the subject of principal interest. In a portrait this is generally the front of the face; failure to focus correctly in such a case may be artistically disastrous. However, when we have occasion to focus a lens down to one or two feet, we are surprised to find how little depth there is, even at small apertures. For example, a 2-inch lens at f∕8 when focused on objects at 12 inches distance has a depth of field of about half an inch in front of and beyond the focused distance. A small depth of field is sometimes very useful, for instance, as a means of eliminating an unwanted background (Fig. 5.1).

Abstract: A large-aperture single lens with aspherical surfaces to be used as a pickup lens for video disks, especially for tracking the video disk by directly moving the pickup lens. It is preferable that the single lens is made of plastic material in order to make it compact and light in weight. Both refractive surfaces of the single lens are arranged to have positive refractive powers in order to make the working distance of the lens long. Spherical aberration of the single lens is corrected to the degree that the diameter of the circle of confusion thereof is decided approximately by diffraction of light. Both refractive surfaces of the single lens are formed as aspherical surfaces and the shapes of the refractive surfaces are determined so as to correct aberrations including the sine condition to the required range, by taking the error to be caused at the time of manufacture into consideration.