An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. The border between these is sometimes defined using a circle of confusion criterion.
A principal focus or focal point is a special focus:
A diverging (negative) lens, or a convex mirror does not focus a collimated beam to a point. Instead, the focus is the point from which the light appears to be emanating, after it travels through the lens or reflects from the mirror. A convex parabolic mirror will reflect a beam of collimated light to make it appear as if it were radiating from the focal point or conversely, reflect rays directed toward the focus as a collimated beam. A convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex hyperbolic mirror will reflect rays emanating from the focal point in front of the mirror as if they were emanating from the focal point behind the mirror. Conversely, it can focus rays directed at the focal point that is behind the mirror towards the focal point that is front of the mirror as in a Cassegrain telescope.
Adam finds an exciting mate: although a principal focus of epilepsy research has been on ion channels, a ligand-receptor interaction in nuerons may also be important in the disease.(NEUROSCIENCE)
Sep 22, 2006; Epilepsy, one of the most common neurological disorders, is caused by abnormal electrical activity in the brain. The symptoms...