Effective Focal Length (EFL)

Relevant for: ImageMaster^®

The Effective Focal Length (EFL) or equivalent focal length is the distance from the focal points of the lens to the respective principal planes. The EFL determines the magnification of a lens and hence the image size. Because the principal planes are usually inside the lens at unknown locations, the direct measurement of the EFL is difficult.

However, the EFL can be measured quickly and with sufficient accuracy using the method of measuring the magnification of a double bar target. Certified master lenses from NPL (National Physical Laboratory of UK) and PTB (National German Standard Institute) are available at TRIOPTICS and are used for the calibration of the measurement setup. The measurement data are thus directly traceable to international standards.

Relevant for: ImageMaster^® MTF Station