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Infrared Zoom Lens System for Target Detection

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Infrared Zoom Lens System for Target Detection

Issue Time:2022/03/25
This article describes an infrared (IR) zoom lens gadget designed to detect missile signatures at 8 to 13 Bin wavelengths. Additional discussion will involve optical design philosophy as it pertains to this particular issue. When designing an optical system, the most important question is: "Where do you start?" The answer to this question will have a large impact on the successful outcome of the campaign, as the starting point limits the area where the design problem will be solved. The number of lens elements and corresponding degrees of freedom should be sufficient to achieve the desired result without adding more complexity. The choice of material can also be a key factor in this decision, as the nature of the color depends heavily on the choice of material.

1.1.Requirements

The requirement is for near diffraction restricted, high resolution (1 mrad) imaging optics inside the 8 to 13 wavelength vicinity running at f/2 with a transmission extra than 50 percent. 3 distinctive lens modes running over a 3:1 magnification variety are had to cover a 9.525 mm diameter detector for 3 distinctive sets of target range and area of view (FOV). The focal length range is 37. Seventy-six mm to 113.28 mm and the corresponding FOV is ±7.19 tiers to ±2.Forty-one stages. Size and weight obstacles are additional parameters that constrain the layout.

1.2.Type of the optical system

An all-reflective gadget would first-rate meet the spectral bandwidth requirement due to the fact there's no chromatic aberration. One such device has these days been defined inside the literature.1 a set awareness refractive optical machine may be designed to be diffraction restricted for any given set of situations. 3 such structures can then be one by one designed and installed to replace one to the other to cover the 3 units of target variety and FOV. The opposite possibility is a zoom lens which would allow converting from one mode to any other in a non-stop manner. This system could require a multi-element optical device with a few mechanisms for lens travel via the zoom variety. The zoom lens idea became pursued to minimize the dimensions and weight of the optical device whilst retaining the f/no. Requirement.

1.3.Zoom lens types

Zoom lenses are compensated in approaches: routinely and optically. Inside the mechanically compensated zoom lens, the transferring additives journey thru the zoom range in a nonlinear relationship with admiration to each other. Within the optically compensated zoom lens, the shifting elements are related collectively and move as a single unit through the zoom variety. Despite the fact that the optically compensated zoom lenses offer an easier mechanism, they also tend to be longer (than the routinely compensated ones). Additionally, mechanical compensation keeps a consistent image of aircraft location throughout the zoom, whereas, with optical reimbursement, the photo is in exact attention handiest at discrete zoom positions. Mechanical reimbursement turned into selected for this utility because of period constraints imposed by packaging issues.

1.4.The starting point

The optical designer has to select the most likely starting point from among the following possible alternatives:

1)a commercially available, off-the-shelf optical system;

2)a previously designed, in-house optical system;

3)a lens described in the patents or other literature;

4)a thin lens solution.

In this specific case, a thin lens answer turned into decided on because the starting point after putting off the first 3 options from attention. Commercially available IR zoom lens systems did not meet the unique requirements of zoom ratio and f/no. For this software. That is also the actual IR zoom lens structures described inside the patents,2,3 and different literature.Four'6 because it turned out, the skinny lens approach was quite simple to devise and carry out.

1.5. First-order properties

An asymmetrical afocal telescope of unit energy can be built with the aid of placing a negative lens halfway between equal fine lenses so that the lens device is operating at unit magnification. If the middle lens is moved alongside the axis from the mid-position in both courses, the magnification will exchange hastily. Such an afocal gadget is shown schematically in Fig. 1. One of the outer lenses ought to be cam-pushed to preserve the afocal adjustment of the device. This sort of zoom attachment is described through Rudolf Kingslake in a paper at the improvement of the zoom lens.7 the first-order parameters of a three:1 afocal zoom attachment defined in Kingslake's paper are supplied in desk I. The lens moves of this device are plotted in Fig. 2 as a feature of magnification.

An afocal attachment in front of a fixed imaging lens was used as the starting point for this design. A 3:1 zoom ratio is achieved by going from a magnification of l/'/J to V5", v/ith unity magnification in the mid-position (Fig. 3). By placing the aperture stop behind the moving elements, it is possible to maintain a constant f/no. at the image plane without a variable iris.

1.6.Computer optimization


An evaluation of optical layout applications for infrared-type optical systems has been provided at a previous SPIE technical symposium.10 David grey's pc application is particularly nicely proper for zoom lens programs. His optimization program for robotically compensated zoom lenses (MZOOM) changed into applied for the exact design of this zoom lens. It's far a completely powerful application that optimizes for 9 specific positions throughout the zoom variety concurrently at the same time as maintaining a fixed photo plane over the complete variety. The consumer can input boundary situations to govern such parameters as allowable vignetting, lens thickness, and normal machine duration. The thickness and spacing bounds for the unit focal period device used by grey in optimization are shown in Table III. The dimensions factor in millimeters to the significant system is 109.98, the focal duration of the enter prescription. The tabulation of starting and final lens detail focal lengths presented in table IV suggests that the optimization software was allowed to depart from the starting afocal first-order properties to locate the exceptional solution to the problem. This could also be seen from a comparison of the beginning and final unitized lens separations shown in Figs. Four(a) and four(b). The general period of the afocal element has been allowed to increase by 19.0 mm to achieve higher stability of the aberration residuals over the zoom range. It most effectively took some distinctly cheaper runs from beginning to finish to optimize the machine.

2. Conclusions


This paper has described a simple however powerful zoom lens optical gadget for the IR that offers 1 mrad decision for all conditions of use. This zoom lens is useful for goal detection over a huge set of operating conditions due to the fact the picture plane is usually in consciousness over the entire zoom range. Tolerance issues were presented for preserving sharp consciousness because the zoom components flow to trade the magnification.


The method of the optical layout manner has additionally been provided. The position of the computer has been set forth as a powerful computational device that serves to supplement the conceptual and analytic abilities which the designer brings to his assignment.


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3. References


1. Woehl, W. E., Opt. Eng. 20(3), 450 (1981).


2.Altman, R. M. and Rosenblatt, J. J. of Hughes Aircraft Company, Zoom Lens Optical System for Infrared Wavelengths, U.S. Patent No. 3,825,315 (23 July 1974).


Noyes, G. R. of Hughes Aircraft Company, Long-Wave Infrared Afocal Zoom Telescope, U.S. Patent No. 3,947,084 (30 March 1976). Noyes, G. R., Proc. SPIE 131, 24 (1978).


Jamieson, T. H., Opt. Acta 18(1), 17 (1971).


Cox, A., A System of Optical Design, p. 463, Focal Press, (1964).


Kingslake, R., Journal of the SMPTE 69, 534 (1969).


Welford, W. T., Aberrations of the Symmetrical Optical System, p. 141, Academic Press, (1974).


Riedl, M. J., Electro-Optical Systems Design, 58 (November 1974). Juergens, R. C. and Mann, A., Proc. SPIE 131, 28 (1978).


David Grey Associates Computer Optics Package (COP) MZOOM Reference Manual for Mechanically Compensated Zoom Lenses, Genesee Computer Center, Inc., Rochester, New York (June 1980).


Smith, W. J., Modern Optical Engineering, p. 426, McGraw-Hill, New York (1966).