This special issue in Optical Engineering began with aconversation at Photonics West last year with Dr. DonaldO’Shea. We were discussing the capabilities of currentoptical design programs. In his role as an educator, Dr.O’Shea introduces his students not only to the art of op-tical design, but also to the software tools which are avail-able to be used, or misused, to aid in the design of opticalsystems.Optical design programs have expanded in scope sig-nificantly over the last 10 to 20 years. The speed of com-puters has been a significant factor. Many of you mayremember when computer programs could trace all of oneray surface per second, but this was still a marked im-provement over hand calculations. When programsreached ray tracings speed on the order of 20,000 raysurfaces per second, optical design software had ‘‘ar-rived.’’ Now ray trace speeds can easily exceed 1,000,000on some designs.This increase in ray tracing speed has led to severalchanges in how optical design is performed. The first re-sult is that an optimized design form can be determined ina shorter time. It also can provide designers the opportu-nity to explore other regions of solution space. The op-tions available for constructing merit functions allow al-most any requirement to be considered throughout theentire lens design process.Experienced optical designers can design and analyzetolerance complex systems more efficiently and effec-tively than ever before. The basic functionality of the de-sign program more than meets the needs of most designprojects. Properly constructed and constrained merit func-tions can be used to direct the program to one or severalpossible solutions in a relatively short time frame. In-cluded tolerancing capabilities can be applied to deter-mine the best design candidate in terms of performance aswell as manufacturability.Additionally, the design codes are also becoming morepowerful. Calculations, which may have been neglectedpreviously because the amount of time and computer re-sources required, can now be readily performed. Thefunctionality of current software, in many ways, goes wellbeyond simple geometric ray tracing and aberration cal-culation. Many of these new capabilities have been addedto the various programs to try to keep up with needs ofdesigners who need to ‘‘push the envelope’’ of the avail-able software to reach the desired goals.During my chat with Dr. O’Shea, I mentioned that, inmy view, about 90 of the features of most of the designprograms go virtually unused. In part, this is legitimatelydue to the fact that many designs do not require many ofthese capabilities. Much about the process of optical de-sign today is very similar to that done long before thearrival of the computer and userfriendly design codes. It isvery possible that one of the reasons designers do not takefull advantage of the programs is that often we do nothave the time to simply explore the new software releasesas they arrive. We simply look at the changes that areapplicable to our current designs, fully intending to fullyread the documentation when the time is available. Thisleads to the reasons for having this special issue. The firstis to allow optical designers to show other designers theissues that have been dealt with in new ways. The secondis to let everyone look at optical design programs in newways.Papers were submitted concerning several aspects of‘‘pushing the envelope’’ including user-defined or otherspecial surface shapes, specialized analysis capabilities,interactive calculations, and others.The first paper by Descour et al. discusses using singlevalue decomposition to determine the alignment sensitiv-ity of extreme ultraviolet lithography projection cameras.In this case, software was written to modify the design toinclude the desired misalignment modes, and then to takeinformation returned from the design program for use inan external application. The paper by Stone describes ageometric method for modeling many aspects of inter-ferometric systems. The goal is a method that allows in-terferometers to be modeled as actually used. The paperby Rolland discusses the design of head-mounted dis-plays, including the use of specialized analysis tools tomodel accommodation and distortion. These are impor-tant to analyze the system from the perspective of usabil-ity. The paper by Rayces and Rosete-Aquilar discusses amethod for designing an optical system that can be usedto duplicate the wavefront errors of another optical designover the entire field of view. This is a very powerful toolwhich can be used to generate corrector optics whichwork over the entire field-of-view of the original opticalsystem. The next paper, by Rogers, discusses the toleranc-ing of null lenses as part of the end-use design. This pro-vides a correlation between the tolerancing of the nulllens and the performance of the system under test. The