Image is a two dimensional representation of a real object, produced by focusing rays of light. Image plane is the plane commonly at right angles to the optical axis at which a sharp image of the subject is formed. The nearer the subject is to the camera, the greater the lens image plane distance. Impressionism is an art movement in which painters broke away from the techniques of continuous brushstrokes and clearly expressed detail. They were largely concerned with the effects of light and color.
Incident light is light falling on a surface, as opposed to reflected by it.
Incident light attachment is an accessory for a hand held exposure meter which allows it to give incident light readings. Many models come with this accessory permanently attached. Incident light reading is a measurement, by light meter, of the amount of incident light falling upon a subject. The light meter is placed close to the subject, pointing towards the main light source. Indicator chemical is a neutral chemical which can be added to a sample of a solution to indicate its pH level or the presence of hypo.