Focal length measurement
The focal length is the distance from the focal points of a lens to the assigned principal planes. The focal length determines the magnification effect of the lens and therefore also the image size. As the position of the principal planes can often not be determined precisely, it is difficult to measure the focal length directly.
However, the focal length can be determined quickly and with sufficient accuracy by measuring the magnification of a double slit image. TRIOPTICS uses certified lenses and objectives from the PTB (Physikalisch-Technische Bundesanstalt) to calibrate this measurement method. The measurement results and accuracies are therefore directly traceable to international standards.
OptiSpheric® is the industry standard for non-contact inspection of basic axial optical and mechanical parameters and is used worldwide to fully measure and qualify single lenses – as well as intraocular lenses – and optical systems. The world’s largest laboratories and major optics manufacturers rely on TRIOPTICS optical inspection systems.
Knowledge base
Measurement of power, add power and cylinder in compliance with ISO 11979
The OptiSpheric® IOL bench is using the imaging of an object through the lens under test. The resulting image is analyzed in order to evaluate the parameters of the lens (Power, Imaging quality through MTF calculation, energy distribution, Strehl ratio, and more…). Using this imaging technique is similar to realistic conditions and allows testing any type of IOLs designs.
Different types of target are projected to infinity through a collimator. The lens under test gives therefore an image of the target in its focal plane. A measuring CCD microscope is used for analyzing the image by the help of an autofocus mechanism. The instrument also includes different aperture sizes and different imaging objectives chosen automatically by the system according to the power of the lens under test. The wavelength used for the measurement is 546 nm as requested in the ISO 11979 standard.
Setup for In-Situ measurement
Power measurement principle
Power, add power and cylinder are measured from the magnification of a double slit test target. The powers are determined in each focal planes of the IOLs, two different focal planes in case of a bifocal lens, two different crossed focal planes in case of a toric lens, four different focal planes in the case of a bifocal toric IOL, etc. The add power is calculated by subtraction of the near and far powers and the cylinder is calculated by subtraction of the crossed directions powers of a toric lens.Our Newsletter – Your advantage in knowledge
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