The evaluation and theory of operation of optical imaging systems is usually predicted on the assumption that the object is incoherently illuminated; and hence the image is formed by a linear superposition of intensities. This basic assumption is not justified in many situations and can lead to differences in the nature of the image. More particularly the effect on the measurement of image detail can be seriously affected by the partially coherent nature of the illumination.

TELEPHOTO LENS - a positive front component widely separated from a negative rear component. The second principal plane lies outside the end of the system. Its advantage is compactness in the lens barrel length for a given focal length (f). A normal lens gives better definition and covers a wider field at a higher relative aperture than a telephoto lens.

A technique to obtain, optically, quantitative heat transfer distributions on wind tunnel models in short-run duration facilities is discussed. The phosphor coating is very sensitive to temperature and the activating ultraviolet radiation intensity but insensitive to aerodynamic surface loads and surface contamination. These characteristics, combined with millisecond response time, have made accurate thermal mapping practical under transient conditions. Visible and infrared radiation from the gas cap on blunt bodies has been effectively filtered without impairing the usefulness of the phosphor.

The question of the nature of light is not new, but goes back to antiquity. Today most general physics texts, if they make any attempt to deal with the historical aspect of the question, devote at most a few sentences to the classical Newtonian-Huygens controversy regarding the corpuscular versus the wave nature of light. A few texts add a statement to the effect that some of the ancients considered light to be something emitted by the eye, and drop the matter there. Here we shall fill in more details about these ideas.

The generation of accurate two-dimensional auto- and cross-correlo grams as related to optical signal processing is described. The development and design considerations of a simple electro-optical equipment are outlined and the parameters explained, and the principle of operation is discussed. The article then shows possible applications for sonar displays in the field of target recognition and tracking. The final sections deal with correlograrns of small objects and complex images.

A knowledge of reflectance of refractory materials at high temperatures is required for the design of heat shields of reentry vehicles, nose cones of ballistic missiles, rocket nozzles, combustion chambers, leading edges of airfoils operating at supersonic velocities, and many other structures and parts for aerospace applications. In many cases, however, published values for the reflectance of refractory materials at high temperatures are of low precision and questionable accuracy. It is not at all unusual for reflectance values of what is reported as the same material at the same temperature to vary by as much as a factor of two.