Variable Focal Length Zoom Lens

Zoom principle：

Optical Basics: Moving the zoom group inside the lens changes its focal length, which in turn changes the field of view and image magnification.

Key Relationships: Changes in focal length affect both magnification (magnification ∝ focal length) and depth of field (the longer the focal length, the shallower the depth of field).

Typical Structure:

• Fixed group: Fixed in position; performs the primary imaging function.

• Zoom group: Moves along the optical axis and adjusts the focal length by changing its distance from the fixed group.

• Compensation group: Included in some lens designs to correct aberrations or keep the image plane stable.

Applications：

1. Photography and videography

News & Documentary: 24–70 mm zoom for quickly switching between scenes and capturing breaking news.
Sports & Wildlife: 70–200 mm and 100–400 mm telephoto zooms for capturing dynamic subjects at long distances.
Film & Video: Cinema zoom lenses (e.g., 16–35 mm T2.8) support smooth zooming for the "dolly zoom" (also known as the Hitchcock zoom), in which the background perspective shifts while the subject size remains constant.

2. Surveillance & Security

Zoom surveillance lenses (e.g., 2.8–12 mm) allow remote focal length adjustment, supporting both wide-angle monitoring and detail recognition. They are commonly used in airports, shopping malls, and other locations.

3. Industrial & Medical

Industrial Inspection: Zoom lenses used with microscopes or endoscopes adjust magnification to inspect part details.

Medical Equipment: The zoom function of surgical microscopes helps surgeons switch between a macro field of view and a detailed, close-up view for fine procedures.