PSF / MTF Measurement System
Background
A special measurement system for determination and validation of imaging properties of optical components has been designed at the ITIV. It enables the determination of imaging properties and hence the optical quality of monofocal and mutifocal optical component . The measurement is according to EN/ISO11979.
Our measurement, validation and certification services are frequently used by industry, e.g., concerning the optical quality of bifocal intra ocular lenses (IOL) or bifocal contact lenses. The ability to validate multifocal systems is a big advantage compared to other commercial devices.
Functional Principle
Basic principle for the validation of the imaging properties of an optical component is the measurement of the Point Spread Function (PSF , DIN/ISO 9334-9336). The PSF is comparable to the Dirac impulse known from analogue electronics transferred to the optical system. By analysing the PSF imaged through the optical device under test (ODUT) the optical properties of the ODUT can be derived.
For this calculation, the most important criterion is the resolution of the system, e.g., the maximal line density (spatial frequency) that can be distinguished after imaging through the ODUT. A tool to determine this is the Modulations Transfer Function (MTF ). The MTF can be derived from the PSF by Fourier transformation.
Measurement System Setup
A laser source is collimated by a special high precision optical system. This highly parallel light beam is directed onto the ODUT. Using a high resolution and high precision commercial digital camera the magnified image of the focus (equal to the PSF) is recorded. Afterwards a personal computer calculates the optical properties of the ODUT.
For measurements of intra ocular lenses (IOL) or contact lenses the optical properties of the typical human eye have to be simulated.
In the case of the intra ocular lens this is done by an artificial eye which simulates the optical properties of the cornea (according to EN/ISO 11979). The IOL itself is measured inside a bath of physiologic solute since otherwise the refraction properties as well as optical errors would be increased substantially.
Contact Lenses on the other hand need an eye phantom that also simulates the surface properties of the natural cornea as well as the very challenging task of generating the same moisture conditions then when applied at the human eye.
Services
The ITIV offers services in the fields of optic design and optical instrumentation. Due to our long-time experience the group has a profound expertise especially in the field of validation of imaging properties of optical components. This makes the ITIV a competent partner for industrial research and development projects. The services offered include measurement and validation as well as certification.