Final answer:
The edge distortion problem in image intensification tubes is called pincushion distortion, which causes the image to bow inward like a pincushion.
Step-by-step explanation:
The edge distortion problem in image intensification tubes is known as pincushion distortion. This type of distortion typically occurs when the magnification of an image changes with the distance from the optical axis of the tube, causing the image to bow inwards towards the center, much like the shape of a pincushion. This effect is particularly prevalent in image intensifier tubes used in night vision devices, where electronic image enhancement is employed. The other options listed, such as vignetting, veiling glare, and the pinhole effect, also relate to image quality but are distinct phenomena. Vignetting refers to a reduction in an image's brightness or saturation at the periphery compared to the image center. Veiling glare is a flare or haze that spreads across the image from a bright light source. The pinhole effect, while not a standard term for image distortion, could imply an improvement in image sharpness when viewing through a small aperture, as light rays are more effectively focused.