tube lens focal length

The focal length of the tube lens, which focuses light gathered by an infinity-corrected objective lens to form an image. Longer tube lens focal lengths allow for additional optical components to be introduced to the light path.

Synonyms: tube lens focal distance

Related MicroscopyU Article

Tube Lens Focal Length

As the focal length of the tube lens is increased, the distance to the intermediate image plane also increases, which results in a longer overall tube length. Tube lengths between 200 and 250 millimeters are considered optimal, because longer focal lengths will produce a smaller off-axis angle for diagonal light rays, reducing system artifacts. Longer tube lengths also increase the flexibility of the system with regard to the design of accessory components.