PARALLEL PROCESSING tools for today's optiker

axis focused spot of the same lens is also shown in the figure. As expected, the off-axis spot is free from aber­rations and the two spots are essentially identical.

It is not difficult to design an aplanat with the characteristics of the lens in the above example; a spe­cific design is shown in Figure 8. The various parame­ters of this meniscus, which consists of two conic sur­faces, are listed in the figure's caption.

Offense against the sine condition Let us now examine the special case of a lens in which the ray heights have been made equal at the principal planes. Here (x, y) = (x', y'), and the dif­ference between the actual and the ideal (i.e., aber­ration-free) emergent wavefronts is

Note that S χ and Sy are proportional to sinθ, but in the present case it is tanθ that is magnified by 1/m. A Taylor series expansion yields

To a first approximation, therefore, the difference be­tween sinθ and tanθ is proportional to sin3θ. This difference, when inserted into Eq. 4, produces prima­ry coma. Thus, when the rays that enter at a given height on the first p.p. emerge at the same height on the second p.p., perfect imaging of the axial point re­sults in comatic imaging of the near-axis points.

Similar arguments may be advanced for systems that violate the sine condition in ways other than described above. In general, offense against the sine condition results in primary and higher order coma in near-axis regions of the image plane.

The image of a diffraction grating An appealing argument in favor of the sine condition involves the image of a diffraction grating.10 Consider a small grating of period P placed perpendicular to the optical axis in the object plane of the system of Figure 3; the illumination is coherent, collimated, and mono­chromatic with wavelength λ. The nth diffraction order leaves the grating at the Bragg angle θn relative to the

optical axis, where sinθn = nλ/P. In the image plane, the grating period is mP, where m is the transverse magnification of the system. Therefore, to obtain a dis­tortion-free image, it is necessary that all sinθn be magnified by 1/m; in other words, the sine condition ought to be satisfied.

References 1. E. Abbe, Jenaisch. Ges. Med. Naturw. (1879); also Carl. Repert. Phys. 16,303

(1880). 2. C. Hockin, J. Roy. Micro. Soc. 4 (2), 337 (1884). 3. A.B. Porter, Phil. Mag. 11(6), 154 (1906). 4. M. Born and E. Wolf, Principles of Optics, 6th ed., (Pergamon Press, Oxford, U.K.,

1980). 5. M.V. Klein, Optics, (John Wiley & Sons, New York, N.Y., 1970). 6. J.M. Stone, Radiation and Optics, (McGraw-Hill, New York, N.Y., 1963).

7. A.E. Conrady, Applied Optics and Optical Design, (Dover, New York, N.Y., 1957).

8. The simulations reported in this article were performed by DIFFRACT™, a product of MM Re­search Inc., Tucson, Ariz.

9. J.W. Goodman, Introduction to Fourier Optics, (McGraw-Hill, New York, N.Y., 1968).

10. Douglas Goodman, private communi­cation.

OPN Contributing Editor Masud Mansuripur is a pro­fessor at the Optical Sciences Center, Univ. of Ari­zona, Tucson, Ariz.; masud@u.arizona.edu.

Electronic Information

The OSA-Library Connection

BY KATHY NORDHAUS

Moving into new arenas is often a daunting proposition, so when

OSA took its first steps into elec­tronic publishing, the Society began to look for ways to ensure that its products would be marketable. One place OSA turned to was its Library Advisory Committee (LAC). Origi­nally an ad hoc committee formed in 1993 to build firmer links to the

Figure 7 . (a) Distribution of phase at the first p.p. of an infinite-conjugate lens having NA = 0 .75 and f= 4000λ. The entrance aperture radius is 30000λ, and the incident beam propagates at θ = 0.076° relative to the optical axis. The grayscale covers the interval from -180° (black) to +180° (white). (b) Distribution of phase at the second p.p. Since the lens satisfies A b b e ' s sine condition the exit aperture radius is 4536λ. (c) Loga­rithmic plot of intensity distribution at the focal plane showing the axial focused spot (center) and the off-axis spot corresponding to an oblique incidence angle of θ = 0.076°. The spots are nearly identical; both are substantially free from aberrations.

Figure 8. Aplanatic men iscus brings coll imated b e a m s to diffraction-limited focus within its focal plane in the vicinity of the optical axis. This 4-mm diameter lens has f = 2 . 6 7 3 3 m m and NA = 0 .75 . The refractive index of the lens g lass is n = 2 .49486 , its th ickness at the center is 1 m m , and its conic sur faces have the following radii of curvature and conic constants : first surface R c = 2 . 2 6 8 7 5 m m , k = -0.20945, second surface R c = 3 . 8 7 4 9 3 m m , k = 0 . 0 8 1 7 3 . The second p.p. is 0 . 2 8 9 4 m m to the right of the first sur face 's vertex.

6 0 Optics & Photonics News/February 1998

PARALLEL PROCESSING tools for today's optiker

science library community, the LAC evolved into a advisory body. The LAC consists of OSA members and senior librarians who represent aca­demic, corporate, and laboratory li­braries. Since LAC members have strong interests in electronic infor­mation and since the library com­munity as a whole is one of OSA's fi­nancially critical customers, the Society asked LAC to provide input on the future dissemination of sci­entific information.

The relationship is symbiotic. OSA learns about the needs of li­braries and LAC's librarian mem­bers are involved in the publishing process, learning about the pres­sures pushing societies toward elec­tronic formats and the economics involved in this activity.

LAC provides a forum for critical feedback to OSA about the concerns and needs of the research communi­ty. These concerns include the use of CD-ROM as an archival format, proprietary versus non-proprietary interfaces, peer-reviewed articles, and journal subscription packages.

A discussion of what librarians and library patrons want in today's world is followed by a look at four specific libraries with varying elec­tronic abilities.

What libraries want Providing quality information to clientele—the library user—is the fundamental concern of librarians. In all types of libraries, users are de­manding desktop access. With re­search and corporate facilities geo­graphically dispersed, librarians have to find ways to get information to customers—they can no longer wait for customers to come to them. Finding quality products that can be networked for reasonable costs is a main goal. Having more databases accessible via the Internet is also crucial since it decreases the prob­lems inherent in using different op­erating systems and search engines (often a frustration as anyone who has done searches knows).

Self-service in the library is an­other important factor. Library

clientele is becoming more comput­er savvy and, in some cases, wants to do their own research. The for­mat for this needs to be logical, and ease of use is critical for both pa­trons and librarians.

Librarians serve their clientele. To accomplish this successfully, they must be aware of who their cus­tomers are—students, faculty mem­bers, research associates, engineers, members of technical staff, etc. Marketing to customers and, more importantly, to non-library users is a necessity these days.

Exploring libraries As mentioned previously, there are many types of libraries, specializing not only in subject matter but also catering to unique sets of clientele. Each of the libraries discussed below (and represented on the LAC) has its unique concerns in addition to those shared with other such institutions.

The John Crerar Library The John Crerar Library at the University of Chicago is an acade­mic institution. Networked infor­mation sources for indexes, ab­stracts, and full-text articles are a priority. The library's clientele is primarily a research community lo­cated in different buildings. The li­brary is very much self-service, with graduate students being the principle customers.

The John Crerar Library has over 50 physics and astronomy journals in electronic format. The library is beginning to add publisher pack­ages, which provide access to more science journals in other disciplines. In addition, the library has a Web page that provides hot links to other resources.

Microsoft Corp. The Microsoft Library, a corporate library, was founded in 1983 with 1 employee, 20 software packages, 50 books, and 1 beanbag chair. Today, there are 43 library employees in 5 li­braries supporting 20,000 Microsoft (MS) employees. The libraries cur­rently provide books, technical re­

ports, software, customized Intranet delivery of tools, and information for self-service use. A research team, aligned with the MS product and service divisions, provides cus­tomized information for on-demand research, including customized news services, Web pages, and training re­sources and tools.

MS employees at all levels use the library services regularly. In an aver­age month, 2,500 e-mail requests from MS employees are received by the library; over 1,100 employees are assisted at the reference desks; and over 400,000 news articles are distributed via e-mail to market-focused news distribution lists. At the same time, the Library adds 1,800 items to the collection; circu­lates 5,000 items worldwide; and fills over 4,000 article requests, in­cluding 2,500 requests for individ­ual reports from the market re­search collection.

The Ruth H. Hooker Research Library The Ruth H. Hooker Research Li­brary, located at the Naval Research Laboratory (NRL), supports the re­search mission of NRL by providing access to a broad range of scientific and technical information.

In response to a 1990 user sur­vey, in which the researchers indi­cated a need to have information readily available in laboratories and offices, the Library began an ambi­tious program to provide desktop access to databases, reference tools, agency publications, journals, and other information resources. In 1992, the Library introduced an In­foNet for telnet access to library cat­alogs, CD-ROM and online data­bases, travel information, and laboratory "management informa­tion" such as supply store catalogs. The migration of Info Web's charac­ter-based services to the Web began in 1995. The full spectrum of library electronic services is now available.

InfoWeb also serves as an inter­face to NRL's Digital Library Initia­tive known as TORPEDO, which provides researchers the ability to search and browse the contents of

Optics & Photonics News/February 1998 61

PARALLEL PROCESSING tools for today's optiker

over 160 journals that the library has mounted locally. TORPEDO in­cludes access to over 6,000 reports from the library's collection (a sub­set of 185,000 reports that have been digitized since 1991), NRL press re­leases, journal articles, and confer­ence papers.

RTIS Libraries Raytheon TI Systems (RTIS; for­merly, Texas Instruments Defense & Electronics Group) has four cor­porate libraries serving the research needs of its geographically dis­persed employees. The libraries provide desktop access to several engineering and business databases accessed on an internal network. The RTIS Libraries' goal is to move toward Web-based products as they become available. The libraries provide customer stations for ac­

cess to the Department of Defense Technical Information Center's technical reports database (DROLS), OSA's Journals Index, Air Universi­ty Library Index to Military Period­icals, and Jane's Defense Equip­ment Library, as well as other reference tools.

In conjunction with the Texas In­struments libraries, RTIS libraries provide desktop access to an online catalog and a Web page provides ac­cess to all types of hot links.

Getting involved These four libraries and their ser­vices illustrate a small sampling of the types of libraries using electron­ic resources. While librarians are a key element of a successful library, patrons are also vital. OSA members need to look critically at their acade­mic, corporate, or laboratory li­

braries to see that the information they need is being provided—and in a medium best suited to them.

Customers should find ways to communicate their concerns to li­brarians. One way is to join a library committee whose members often assist in testing new products for vi­ability, subject content, and ease of use; help expand current or create new services; and review journal packages.

OSA members wishing to share concerns about the publication of OSA electronic journals can contact LAC Chair Alexander Sawchuck (University of Southern California) at sawchuck@usc.edu.

Kathy Nordhaus is a senior information specialist at Raytheon TI Systems in Dallas, Texas. Contributors to this article include Laurie Stackpole (NRL), Cindy Wil­son (Microsoft Corp), and Kathleen Zar (John Crerar Library).

Patent Design

A Wide-Range 35 mm BY J. BRIAN CALDWELL

Patent: U.S. 5,694,253 Issued: December 2, 1997 Title: High Zoom Ratio

Zoom Lens Example: #2 of 3 Inventor: Atsushi Shibayama Assignee: Nikon Corp.

Zoom lenses with a focal length range of 28-200 mm

have become very popular as an "all-in-one" lens for 35-mm SLR cameras. To date, this class of zoom lens is represent­ed in U.S. literature by only a few, fairly recent patents.1-3

This month's design is an ex­ample of such a lens by Nikon, and is notable for its compactness and high image quality.

The design shown in Figure 1 has 16 elements arranged into four zooming groups in a positive-negative-positive-positive configuration. Compactness at the wide angle end is achieved by moving all four groups away from the image plane when zooming from short to long focal lengths. This contrasts with

older style positive-negative-positive zoom lenses, where the front group is fixed relative to the image plane, re­sulting in an overall length that is large at all zoom positions.

Focusing is achieved by moving the second group toward the object. A large focal length variation occurs during focusing because this group is the variator. The design is well suited for auto-focus construction because the focusing group is fairly small and does not require a great deal of movement. One drawback to the arrangement is that a different amount of movement is required for focusing on an object at a fixed dis­tance when the lens is zoomed to a different focal length.

Surfaces 6 and 22 are aspheric, and are described by the equation:

where z is the direction along the optical axis, h is the direction per­pendicular to the optical axis, r is the paraxial radius of curvature, k is the conic constant, and a4, a6, a8 and a10 are polynomial deformation

Figure 1. 28.8-194 mm f/3.4-f/5.9 zoom lens for 35-mm SLR cameras.

6 2 Optics & Photonics News/February 1998