Development of an auto-focusing fluid lens system
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Date
2009
Authors
Abdullah, Soran Jalal
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Abstract
Variable focal fluid lenses are gaining popularity in many applications where
glass lenses were once the only source for optical systems. Due to the new
mechanism of the fluid lens, where fluid is the main factor for focus shifting,
application of the fluid lens in an automatic focusing system represents an important
study for verifying the viability of fluid lenses in automated operations. Therefore,
the work undergone in this thesis deals with the development of a fluid lens system
that uses image feedback for focusing information. A software algorithm was
devised to achieve auto-focus operation, by a number of methods, for binary targets
within 1 m distance range. The system comprises two stepper motors – one for
moving the target using a guide rail and the other for actuating the syringe-driven
pump that injects or withdraws fluid into (or out) of the fluid lens chamber. The lens
was made of polydimethylsiloxane (PDMS) polymer which has high optical
transmittance. Distilled water, contained in a fluid chamber, was used as the
actuating medium. A monochrome CCD camera was directly attached to the fluid
lens by an extension tube to capture live images of a binary target. Slope width of
pixels intensity profile along a horizontal line across the binary target was chosen as
the focus measure value. The auto-focus operation independently varied the lens
focal length to arrive at the focused image based on the image feedback analysis. An
error-based focusing method was developed that improved the focusing time over the
normal focusing method. A comparative modulation transfer function study has
shown that the fluid lens image quality resembles that of a glass lens at low spatial
frequency whereas glass lens performs better at high spatial frequency.
Description
Master
Keywords
Biological Science , Fluid lens system