Development of compact optical zoom lenses for integration in mobile phones is the goal of many companies.
Optical zoom lenses change their focal length by the movement of lens elements or change in surface curvature or
refractive index and this complicates the zoom lens design. Extended depth-of-
field (EDOF) techniques provides
the mean to simplify and miniaturize zoom lens designs with moving lens elements and a new EDOF optimization
technique is presented. Finally, the starting point and an example of a compact optical zoom lens design with
EDOF is also described.
The use of hybrid optical-digital techniques facilitates improved optimisation of imaging systems. It involves the
combined use of optical coding of an image using pupil-plane phase-modulation of the transmitted wavefront and postdetection
digital decoding. Previous research in hybrid imaging tends to emphasize constancy of the modulation transfer
function with aberrations and ignore the significant variations in the phase transfer function. We show that the
restoration artefacts introduced by phase mismatch effects can also be used to deduce the defocus PSF, and when this is
achieved, an overall improvement in image quality can be attained. Both numerical simulations and experimental
images of hybrid imaging systems are presented.
Based on an analytical analysis of the optical transfer function in an optical system with wavefront coding, specifically
with a cubic phase mask in the aperture stop, we explain that such systems have image artefacts in the restored images
and that these are manifested as replication artefacts. To remove image artefacts we propose to store a set of defocused
point spread functions such that a single defocused image can be restored to a set of images, wherein one of them is
without image artefacts. The image without image artefacts is determined with a new metric which we define in the
wavelet domain.
The design of modern imaging systems is intricately concerned with the control of optical aberrations. Traditionally this involves a multi-parameter optimisation of the lens optics to achieve acceptable image quality at the detector. There is increasing interest in a more generalised approach whereby digital image processing is incorporated into the design process and the performance metric to be optimised is quality of the image at the output of the image processor. We will discuss the trade offs involved in the application of this technique to low-cost imaging systems for use in the thermal infrared and visible imaging systems, showing how very useful performance enhancements can be achieved in practical systems.
Traditional zoom lens designs employ multiple moving lens elements to provide simultaneous control of focal length and
focal plane. We present an example of a simplified and compact zoom lens design by employing a single moving
element to control only the focal length. In this zoom lens, wavefront coding is used to control the defocus. We describe
the principles of operation with special attention to image processing. We simulate imaging and image restoration
capabilities and present that the zoom lens provides high imaging quality.
Traditional zoom lens designs employ multiple moving lens elements to provide simultaneous control of focal length and
focal plane. We present an approach to a design of a simplified zoom lens by employing a single moving element to
control only the focal length. We show that the defocus in miniaturized zoom lenses with a single moving element can be
corrected by the use of wavefront coding, although this introduces a modest reduction in signal-noise-ratio. As an
example, we present a design of a miniaturized 10 mm long wavefront coded 2.3x optical zoom lens with a single
moving lens element.
The design of modern imaging systems is intricately concerned with the control of optical aberrations in systems that can
be manufactured at acceptable cost and with acceptable manufacturing tolerances. Traditionally this involves a multi-parameter
optimisation of the lens optics to achieve acceptable image quality at the detector. There is increasing interest
in a more generalised approach whereby digital image processing is incorporated into the design process and the
performance metric to be optimised is quality of the image at the output of the image processor. This introduces the
possibility of manipulating the optical transfer function of the optics such that the overall sensitivity of the imaging
system to optical aberrations is reduced. Although these hybrid optical/digital techniques, sometimes referred as
wavefront coding, have on occasion been presented as a panacea, it is more realistic to consider them as an additional
parameter in the optimisation process. We will discuss the trade-offs involved in the application of wavefront coding to
low-cost imaging systems for use in the thermal infrared and visible imaging systems, showing how very useful
performance enhancements can be achieved in practical systems.
Photo-thermo-refractive (PTR) glasses have shown high efficiency and stability for different applications in laser systems. One of the applications of diffractive elements in PTR glasses is to use them for high power laser beam control and combining which requires an increase of the size of these elements. The opportunities of recording large aperture Bragg gratings by using a translational (multi-frame exposure) technique and by using an Ar+ ion laser with higher power operating at 334.5 nm and 351 nm are studied. It is shown that photosensitivity of PTR glass at 334.5 nm and 351 nm is comparable to that of 325 nm. Because of higher power at 334.5 nm and 351 nm, the recording of large aperture holograms at these wavelengths is possible. Large-aperture holograms produced by multi-frame technique are demonstrated.
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