what are Optical Instruments?

The human eye is a remarkably effective organ, but its range can be extended in many ways by optical instruments such as eyeglasses or contact lenses, simple magnifiers, motion picture projectors, cameras (including TV cameras), microscopes and telescopes. In many cases these devices extend the scope of our vision beyond the visible range; satellite-borne infrared cameras and x-ray microscopes are examples.

In almost all cases of modern sophisticated optical instruments, the mirror and thin lens formulas hold only as approximations. In typical laboratory microscopes the lens can by no means be considered “thin.” In most optical instruments lenses are compound; that is, the are made of several components.

In this section we consider optical devices that are designed to produce an enlarged image; we want something to appear larger than it appears to the unaided eye. The lateral magnification is an incomplete measure of the apparent size of an image produced by an optical system. An optical system might produce an enlarged image (|m|>1), but may place that image so much farther from us than the object that it would actually appear to the observer to be smaller than the object that it would actually appear to the observer to be smaller than the object. Even though the lateral magnification may be greater than unity, and thus the image size greater than the object size, the net result is not what the observer would call a “magnified” image.