Variable focal length zoom lens

Zoom principle
Optical Basics: Changing the equivalent focal length of the lens by changing the position of the moving lens group (zoom group) in the lens to achieve a change in the angle of view and imaging magnification.
Key formula: Focal length changes affect imaging magnification (magnification∝ focal length) and depth of field (the longer the focal length, the smaller the depth of field).
Typical structure:
Fixed group: fixed position, undertake basic imaging functions;
Zoom group: can move along the optical axis, adjust the focal length by changing the distance from the fixed group;
Compensation group: In order to correct the aberration or keep the image plane position stable, some lenses add a compensation movement group.

Application scenarios
1. Photography and videography
News & Documentary: 24-70mm zoom to quickly switch scenes and capture breaking scenes;
Sports & Ecology: 70-200mm, 100-400mm telephoto zoom, long-distance capture of dynamic subjects;
Film & Video: Cinema zoom lenses (e.g., the 16-35mm T2.8) support smooth zoom for "Hitchcock zoom" (the background perspective changes without the subject size changing).
2. Surveillance & Security
Zoom surveillance lenses (e.g., 2.8-12mm) can remotely adjust the focal length to cover wide-angle monitoring and detail recognition, and are commonly used in airports, shopping malls and other scenarios.
3. Industrial & Medical
Industrial inspection: zoom lens with microscope or endoscope to adjust the magnification to observe the details of parts;
Medical equipment: The zoom function of the surgical microscope helps doctors switch between the macro field of view and the angle of view of fine operations.