What feature of the image intensifier is responsible for inverting the image?

The feature of the image intensifier responsible for inverting the image is the electrostatic focusing lens. In an image intensifier, the primary function is to amplify the image created from the input phosphor. The process involves converting the incoming light from the input phosphor into an electron stream, which then passes through the electrostatic focusing lens.

These electrostatic lenses are designed to focus and direct the stream of electrons toward the output phosphor. Importantly, as the electron beam passes through these lenses, it is inverted both vertically and horizontally. This results in the final visible image seen at the output phosphor being oriented in the opposite direction of the original input image.

While the input phosphor converts X-rays into light and the output phosphor converts electrons back into light for display, they do not contribute to the inversion of the image. The photocathode functions to convert light photons into electrons but does not have any direct role in image inversion either. Therefore, the electrostatic focusing lens is key to the image inversion process in the operation of an image intensifier.