Many fixed focus lenses for uncooled state of the art LWIR cameras are frequently factory set at large distance and therefore produce blurred thermal imagery when targets are closer than 80 m. To solve this issue, we propose a freeform based varifocal attachment that consists of two thin Germanium plates and is derived from Alvarez-Lohmann concept. When implemented together with our low-cost f/1.1 65 mm LWIR lens, the varifocal attachment enables sharp thermal imagery from 2 m to infinity. Extensive tolerancing study supports feasibility of this freeform device for future manufacturing.
A compact zoom system originating from a generalized form of the Alvarez-Lohmann (AL) varifocal lens concept is developed and discussed here in terms of its potential future applications in infrared imagers. Design methodology based on the use of different polynomial representations of corresponding freeform surfaces is also briefly outlined. In particular, a targeted polynomial technique, which can reduce the dimensionality of the optimization task, is put forward. Silicon-based AL zoom solution is found especially attractive: it can work in both in MWIR band and quasimonochromatic SWIR channel. Complex freeform surfaces can be generated in Silicon substrates by using dedicated SPDT processes. As a design example, a 3x MWIR/SWIR afocal Galilean freeform zoom is presented which covers a FOV range from 7.4° to 22.5° and offers close to diffraction limited performance.
Compact multispectral imagers often require lightweight, inexpensive, flat beamsplitters working in convergent light. Unfortunately, the use of tilted plane parallel plates (PPPs) as an optomechanical design technique is severely restricted due to the aberrations that PPPs generate in non-collimated spaces. We propose a digital correction method of the image blur introduced by tilted flat beamsplitters working in convergent light. The deconvolution-based results are compared against some known non-symmetric aberration correctors advocated by classic, optical hardware based solutions. This method offers a promising solution for reduction of size, weight and cost of high-performance compact multispectral imaging systems.
We expand the effective size of the eyebox of a magnified telescopic weapon sight by following the movements of the
operator’s eye to create a larger, ‘electronic eyebox’. The original eyebox of the telescope is dynamically relocated in
space so that proper overlap between the pupil of the eye and the exit pupil of the device is maintained. Therefore, the
operator will perceive the entire field of view of the instrument in a much bigger spatial region than the one defined by
the original eyebox. Proof-of-the-concept results are presented with a more than 3.5X enlargement of the eyebox
volume along with recommendations for the next phase of development.
The classic method of design centering commonly used to increase the yield of electronic circuits is
employed to improve manufacturability of complex lens designs. The approach uses the results of
Monte Carlo (MC) statistics to iteratively center the nominal design on a new point that shows an
improved yield. Rather than just employing the MC lens run for routine as-built performance forecast,
the results of the simulation are re-used to find the changes in the nominal design parameters values
which will increase the yield. The centers-of-gravity (COG) algorithm is selected as a quick and easy
method of shifting the nominal design point in the multidimensional parameter space to the new
location. The classic COG algorithm is modified to avoid situations when the position of either "pass"
or "fail" center of gravity is difficult to determine. Examples of application, which include a wide-angle
IR lens and a plan-apochromat objective for a digital microscope show that such method of lens
design centering is promising, and even a single iteration may result in significantly improved yield.
Although hybrid ( i.e. refractive-diffractive ) surfaces are in common use in optical design there are several
phenomena which affect design MTF that are not routinely modeled in current commercial versions of optical
design software. Typically the details of the diffractive structure are not taken into account and rays are traced
through the hybrid surface employing a vector grating equation which uses the phase gradient associated with
the diffractive definition to calculate a local grating spacing and orientation and from this grating information
a 'diffracted ray' angle. This geometrical-optics based procedure has limitations; (1)it considers only the design
diffraction order, (2)it does not take into account the sub-aperturing effect whereby color correction is reduced
along with zone count , and (3) the model used does not generate an exact blaze profile. In this paper we discuss
progress in application of diffraction-based beam propagation tools in combination with a physical definition of
the diffractive structure to more accurately model these secondary effects on design MTF. Results are given for
some simple lenses and also the effects to be expected for a more complex zoom lens.
The control of optical distortion is useful for the design of a variety of optical systems especially those used for laser scanning. The optics used for focusing a laser beam onto a flat image field must satisfy the f-(theta) condition (the image height is proportional to the input field angle) to produce a constant scan velocity across the image plane. We analyze and compared the optical performances produced by several single surface reflector as line scanning distortion corrector. Our guideline is a distortion less than 0.1% typically used in the industry. For particular reflector we are always able to find the right position for the scanning mirror to produce in the image field a correct scan line. Our results show a linear dependence of the maximum scanning angle which the errors is less than 0.1% and the scanning beam f- number. At the same time, the mirror f-number is inversely proportional to the scanning beam f-number. Then bigger is the mirror f/#, smaller is the size of the scanning spot and the scan angle. We compute four graphs that can be used easily and gives a complete picture of the performance produced from a single reflecting surface as distortion corrector.
In this communication we propose a design combining the advantages of the space invariance of telecentric triangulation with high relative lateral resolution and large measuring volume at the same time. Because the scan motion of the laser beam is decoupled from physical transport of the sensor head, this enables the fast scan in large volume. However we need a large aperture optics as large as the scan areas. We used a liquid mirror as aperture for this scanner. The surface of a spinning reflecting liquid takes the shape of a paraboloid that can be used as a reflecting mirror. This very old and nearly forgotten concept as recently been revived, with success. Low costs, large sizes, high optical qualities are the main advantages of liquid mirrors. The main limitation of liquid mirrors come from the fact that the optical axis must be aligned vertically and cannot be tilted. The prototype involves a stand-off distance of 1.5 meters, a scan length up to 1 meter (telecentric), a depth of view of 1 meter and a relative depth resolution of 1 mm (can be less). The design is based on the auto-synchronized scanner and is well corrected for field scanning distortion (f-0).
Triangulation systems that are based on an autosynchronized scanning principle to provide accurate and fast acquisition of 3D shapes are able to scan large fields. It is done generally by a coordinate measuring machine (CMM) carrying a small-volume 3D camera. However the acquisition speed is limited by the CMM movement and also by the image fusion time required to get the complete 3D shape. This paper describes some practical consideration for large volume 3D inspections with emphasis on telecentric scanning. We present the analytical and the optical design of a large telecentric scanner using a large reflective surface. Some results of the laboratory prototype will be presented. We also discuss applications and the viability of this new approach.
Since liquid mirrors are potentially useful in science (e.g., astronomy, atmospheric sciences, and optical testing), work has been undertaken to determine whether they are technologically feasible. A testing tower has been equipped with a scatterplate interferometer interfaced with a CCD for data acquisition and a microcomputer for data analysis. This equipment was used to test a 1.5-m-diameter f/2 liquid mirror, showing that it is diffraction limited; interferometric measurements give Strehl ratios of order 0.8. A 2.7-m-diameter liquid mirror and astronomical observatory presently under construction is briefly described.
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