An image is the structured pattern of light created when rays from an object pass through an optical system and converge at a focal plane. A real image can be projected onto a screen or sensor, while a virtual image appears to originate from a point behind the lens or mirror and cannot be projected. Image quality is determined by the system's ability to resolve detail and minimize aberrations.
Heard on the job
Adjust the condenser lens until the image of the filament is sharp on the back wall.