QPI wavefront technology
Iatia's QPI provides a digital megapixel wavefront imaging solution.
QPI generates its wavefront image from a minimum of two digital camera images at different focal planes. QPI's wavefront resolution is that of the digital imaging sensor (camera) which can be in the megapixels.
In contrast, conventional Shack-Hartmann wavefront systems use resolution limited lenslet arrays.
The QPI wavefront system
QPI wavefront technology sensor data
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Processed QPI wavefront map
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The QPI wavefront system requires two conventional digital images captured at different focal planes to generate a wavefront map. The resolution of the QPI wavefront map generated is limited only by the resolution of the digital sensor used rather than any specialised optics, such as a lenslet array in a Shack-Hartmann wavefront system.
The benefits of QPI's megapixel wavefront data include:
- increased dynamic range of application (ability to measure large lower order aberrations)
- sensitivity to higher order aberrations
Shack-Hartmann systems
Shack-Hartmann sensor data1
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Processed Shack-Hartmann image (25x25 pixel array)
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The Shack-Hartmann system consists of an array of lenslets of the same focal length. Each lenslet is focused onto a digital sensor. An incoming wavefront (from an eye) will cause a deviation of each lenslet's focal spot. This deviation corresponds to the local tilt of the wavefront. The measurement of deviations from each lenslet's focal spot allows the approximation of the wavefront.
Inherent limitations in the Shack-Hartmann system include:
- resolution is limited to the number of lenslets in an array
- lenslet light collection and focal spot centroiding are less effective the smaller the lens gets
- crossover of focal spots reduces the dynamic range of Shack-Hartmann systems.
- the system assumes that the wavefront is locally flat over the diameter of each lenslet. Large lower order aberrations and higher order aberrations can cause blurry and overlapping spots which are difficult or impossible to localize
Acknowledgements
- "Shack-Hartmann sensor data" image courtesy of Dr Andrew Metha, Vision and Biophotonics Laboratory, Department of Optometry and Vision Sciences, The University of Melbourne, Australia.