Lens extenders, shown here, install between the main lens and camera body, multiply the focal length of the lens and decrease the effective aperture. Comparatively, extension rings are used for macro work to allow a given lens to focus at a closer distance.

MidOpt lens extenders convert CCD/CMOS lenses to a multiple of their focal length. Particularly suited to machine vision applications, they increase the focal length (zoom in the image) while lowering depth of field. This will lower the sensitivity of the lens by approximately 1 f/stop per multiplier.
- Focal length is shifted to the telephoto side by a factor of the multiplier (2.0x, 4.0x, etc.).
- f/# of the original lens is not affected.
- Only the telephoto side of a main lens can be used, the picture corners are eclipsed at wide angle.
- The Minimum Object Distance becomes x times that of the original lens.

Calculating Focal length and Aperture

The math is simple:
• Multiply the lens' focal length in mm times the "X" (1.5X, 2X, etc.) to find the focal length that will result.

The same is true of f/stops:
• Either multiply the lens' max aperture times the "X", or simply add one full stop when using the 1.4X or two full stops when using the 2X
• They DO NOT effect Minimum Focus Distance.

A : B : C