OOPs!: Trials and travails in the Observatory’s Optics Projects

The first issue of optics is sight. What do you see? How clear is the image? Is it accurate? For astronomers and telescope makers, these questions define the limits of observation, analysis, and conclusion. Through the history of Harvard College Observatory (HCO), the Smithsonian Astrophysical Observatory (SAO), and the Harvard & Smithsonian Center for Astrophysics (CfA), optical science has formed the foundation of scientific production. In peacetime, when astronomers developed their sky photography, and in wartime, when they diverted their eyes to more worldly reconnaissance, the principle of improved sight — a deeper field, a clearer image, with more accurate colors — has remained at the core of the work. From the early era of telescope building, through to the current age of digital imaging, opticians in Cambridge have always labored to open the windows to the cosmos.

The 15-in Great Refractor telescope, the first monumental instrument at the Harvard College Observatory, was a world-renowned marvel of construction and potential. But while the director was pleased with the lens, he had concerns about certain features of the mounting. Screws sat in inconvenient locations, and awkward metric markings surrounded the small, fragile clocks and dials. To address these problems, he contacted the Cambridgeport based telescope maker Alvan Clark, whose optical company, Alvan Clark and Sons, could rebuild the outfitting. Their most significant addition attempted to adapt the telescope to photography, but these efforts produced hazy, distorted images. It was hardly a disappointment — this experiment created some of the first ever astronomical photographs. (Fig. 1 and 2)

Keen on the idea of improving photographic quality, director Edward Pickering worked with Alvan Clark and Sons to produce new telescopes designed for the camera, erecting these instruments in Cambridge, Oak Ridge, and the new southern observatory in Arequipa, Peru. Of 30 telescopes listed by Solon Bailey in 1929, at least half had seen the Clark’s workshop (Bailey 49). Opticians at the observatory supplemented the Clark’s mechanical work with technical exercises and experiments. Charles P. Howard, an astronomer visiting HCO in 1878, left a workbook of optical problems, where he addressed color correction in telescopic lenses, and the paths of light through lenses, in order to determine the focal point after the refraction of different colored rays. But the usefulness of this theory depended on the craftsmanship of the lensmakers. (Fig. 3)

The early observatory also hosted amateur telescope makers, most notably Joel Hastings Metcalf, who furnished the observatory with no fewer than five telescopes. Professionally a Unitarian preacher, Metcalf spent his spare nights at work with astronomical problems, such as comets, asteroids, and astrophotography. Going far beyond just observation, Metcalf’s amateur sense of astronomy sprung from his childhood preference to build his own instruments. The observatory appreciated his skill; Solon Bailey remembers that “He not only computed his own curves for the lenses, but possessed a genius for bringing them to perfection.” (Bailey 269)  He donated many telescopes to the observatory, including a 16-in doublet for photography, but his most famous work, a 13-in triplet telescope half finished at his death in 1925, went to the Lowell Observatory, where Clyde Tombaugh used it in the discovery of Pluto (Bailey 269). (Fig. 4)

Joel Metcalf’s amateur telescope making prefigured an association begun in the 1930’s by technically skilled and resourceful Bostonians. The Amateur Telescope Makers of Boston (ATM) first formed in 1934 as a way for independent hobbyists to share skills and develop the art of lens crafting. Consisting of some teachers, some tradesmen, and many professional engineers, the ATM caught the interest of Harlow Shapley, director of HCO at the time. Shapley arranged monthly lectures on topics in astronomy (which continue today), and provided basement space adjacent to the Great Refactor where the makers could workshop their projects, eventually collaborating on a 20-in reflector telescope. Unfortunately the outbreak of World War II halted this cooperative. Professionals devoted their spare energy to the war effort, and many of these amateur opticians responded to the call of James Baker at HCO, where a new research and development contract demanded the most skilled and studious craftsman. (Fig. 5)

Baker had come to the HCO in 1935 to study astronomy under Harlow Shapley, but he had a long interest in optical crafting (Fig. 6). During his studies for a mathematics degree at the University of Louisville, Baker constructed two telescopes — lenses, mirrors, and mountings — with which he spent hours studying the stars. During his time as a graduate student at Harvard, Baker gravitated towards the optical projects: he participated in the ATM club, built custom equipment for eclipse expeditions, recalibrated other lenses to suit his spectrographic thesis project, and began to theorize about new lens configurations. He was especially interested in distortionless and apochromatic lenses, which could more accurately capture an object’s size, shape, and color. (Fig. 7)

At the outbreak of the war in Europe, late in 1940, military scientists contacted Shapley about experts in optics. On Shapley’s recommendation, Baker visited Wright Field in Ohio to discuss issues related to aerial photography and reconnaissance. At the same time, aware of the growing importance of optics theory in manufacturing, Baker began a summer school course in optics at Harvard in 1940. With a government contract to build new distortionless lenses for aerial photography, and with new sets of eager hands, Baker set up a second optical shop in basement of Building D at HCO, below the storage rooms of the Plate Stacks (Fig. 5). To head this shop, he hired a clerk and a banker — the most talented members of the ATM. (Fig. 8)

The U.S. Army Air Corps initially contracted the optical laboratory for aerial photography lenses, to be produced under the title of NDRC Section 16.1 for Optical Instruments. Still, the team was able to continue small astronomical projects. They built a telescope for the new Tonantzintla Observatory in Mexico, prepared glass plates for HCO’s ongoing sky imaging project, and helped design a coronagraph to better analyze the solar corona during eclipses. However, after Pearl Harbor, the work took on a “more earnest aspect.” (Fig. 9)

After the successful flight of their first aerial lens prototypes in 1942, Baker’s work grew with funding from the Office of Scientific Research and Development (OSRD). Dubbed the Observatory Optical Project — the eponymous OOP — the shop addressed wide angle aerial photography, high altitude optics, night photography, fluorite lenses, and ocean surveillance. They also worked to correct problems of design efficiency, stability, temperature control, and altitude-based automatic focusing, all of which had severely hindered the ability of aerial photography. (Fig. 10, 11, 12)

While this work was directed at wartime reconnaissance, Baker made significant efforts to ensure that his prototypes could find future use in peacetime astronomy. The NDRC made no requirement that all OOP lenses be both distortionless and apochromatic, but without such precise fidelity they could serve little purpose to astronomers. After the war, Baker’s apochromatic flat-field cameras successfully photographed solar eclipses, and his fluorite crystal lenses quickly became “a treat to astronomical eyes.” (Optics News, 16-17).

Such tall orders required a great staff, and Baker found the enthusiasm and skill he needed from members of both the ATM and optics students. Eventually growing to a staff of 47 people — men and women with overlapping duties of administration, construction, and imagination — the OOP moved from HCO to a larger building at the New England Depository Library in Allston, and eventually to a purpose-built building with greater space for experimental machines. (Fig. 13)

In all, between 1941 and 1945, the OOP produced more than 200 prototype lenses and cameras for the NDRC. Once these were ready, Baker brought them to the Army air bases in Texas and Ohio, where they were flown in B-24 and B-17 planes, testing their capabilities on the heartland landscape. Unfortunately, according to Baker, “The Army Air Force isn’t very good at keeping things” — due to lack of space and reasons of military secrecy, many of these artifacts were destroyed, their parts recycled, or otherwise lost in the machine (AIP Oral history). (Fig. 14)

The OOP staff had fully devoted themselves to the war effort, regularly working more that 70 hours per week. The end of the war, and the subsequent shut down of the project, left many of the staff, including Baker, feeling lost and confused. Still he managed to satisfy his itch for optics, working with the Air Force, the CIA’s U-2 program, the Perkin-Elmer Corporation, Polaroid, and continued manufacturing for the observatory, including: the Baker-Schmidt camera, a powerful wide-angle photographic telescope installed in Bloemfontein, South Africa; and the Baker-Nunn camera, used in Fred Whipple’s Moonwatch satellite tracking program. (Fig. 15)

After the war, with the advancement in distortionless optics, astronomers at the observatory saw a new era of advanced observations before them. The Smithsonian Astrophysical Observatory, relocated to Cambridge in 1955, published a report on “The Future Horizons of Optics,” identifying the issue of “seeing” as the primary roadblock in development. While these new telescopes, notably the Baker-Schmidt, could produce photographs of the sky at high resolution and to faint magnitude, astronomers now faced the issues of visual disturbance due to winds and extreme temperatures in the upper atmosphere.

I.S. Bowen, author of the report, acknowledges that little can be done about air turbulence, short of leaving the atmosphere, but astronomers can work to build protective structures and para-optical devices such as filters or temperature control systems, that might stabilize the image. A secondary problem emerged in the process of observation. Whereas by 1900 photographic telescopes could capture a detailed and wide angle field, this next generation of optics surpassed the resolving power of photographic plates and the granular silver-halide formula used to capture the image. As a solution, Bowen proposed a new concept with little precedent in telescopic observation: the use of “photoelectric surfaces” to capture, and more importantly, filter the starlight observed. In other words, digital photography promised the highest resolution images with minimal distortions, and the ability to reduce, correct, or eliminate background light sources.

From here, the speed of development in optics accelerated to such a degree and to such a level of sophistication that it seems our eyes have only just opened. Through fields like adaptive optics (which mechanically provide the solutions to Bowen’s problems of turbulence), photoelectric detection and CCDs (charge-coupled devices — Bowen’s “photoelectric surfaces”), non-visible light detection, space transport and space-based telescopes, the extent and ability of our astronomical seeing has skyrocketed. The CfA established the Optical and Infrared (OIR) Astronomy research division to focus on instrumentation, but all other divisions apply optics as necessary and collaborate to build instruments when their research goals intersect. While there are many incredible optical projects currently at work at the CfA, two bear special mention: the OIR Detector Lab, which designs some of the most sophisticated CCD imaging devices; and the adaptive optics of the forthcoming Giant Magellan Telescope. (Fig. 16)

The OIR Detector Lab designs, develops, constructs, deploys, and maintains the CCDs and other imaging-related devices built for the CfA’s projects. This lab produced the Megacam, a digital camera released in 2015, composed of 36 CCDs that capture a wide field of the sky (Fig. 16). Megacam also consists of software that provides processing opportunities to measure and correct distortions, filter out unwanted cosmic rays, and combine individual images into a mosaic composition with detail and clarity. In these capacities, it seems like Bowen foretold the coming of the Megacam with his ideas about “photoelectric sensors.” There are currently two Megacams in use: at the MMT telescope in Mt. Hopkins, Arizona; and at the Las Campanas Observatory in the Atacama Desert, in northern Chile. These cameras have contributed to studies of weak gravitational lensing, searches for satellite galaxies, and even for objects in our solar system, not to mention the beautiful photographs they can produce. (Fig. 17)

The Giant Magellan Telescope (GMT) will emerge from an international, multi-institutional project to build a land based telescope more powerful than the Hubble Space Telescope. Currently in the works, astronomers will build this telescope high in the Atacama Desert, where the elevation minimizes atmospheric turbulence and disruptions. But to provide the clearest possible image, and one that can hold its own against the Hubble, astronomers and engineers at the CfA are designing an advanced adaptive optics system, wherein flexible mirrors can respond in real-time to the faintest blur in the air. Not only is this work mechanical – in designing the “actuators” that will correct the surface of the mirror -, it also entails the creation of a system to sense wavefronts in the air, such that the actuators can respond on the mirror surface quickly enough. In addition to using guide-stars and lasers to sense atmospheric changes, this wavefront sensing system is comprised of many tiny lenses that focus onto CCD sensors; these sensors read the tilt of light due to distortion and communicate accordingly. As of 2018, this Acquisition, Guiding, and Wavefront Sensing system (AGWS) has passed its “preliminary” design phase and graduated to a new phase of “detailed” design, although its various components have been prototyped and tested since the late 2000s. (Fig. 18)

With a first-light goal of 2024, the GMT has mirrors in various phases of casting, cooling, grinding, and polishing. The adaptive optics system will not just allow for crisp images, but ultimately for clear and rich data, capturing so much light so well that we can better explore exoplanets, their atmospheres, and their potential to host life. If these planets are anything like ours, we find might find a giant mirror reflecting back at us, or perhaps an alien eye, through an alien lens, looking out and seeing as far as it can. (Fig. 19)

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I would like to thank Ken Launie for his help in collecting materials and information for this exhibit. Brian McLeod also provided sound guidance on writing about optical science. Additionally, Joanie Gearin, Daniel Fleming, and the archival staff at NARA Waltham helped navigate the OOP records, and provided excellent reproductions from the dusty collections.

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Reports published by NDRC Division 16.1 – Optical Instruments (OSRD Report No. given)

• “Spherically Symmetrical Lenses and associated equipment for wide angle aerial photography” (6016)
• “Design and Development of an Automatically focusing 40-in f/5.0 Distortionless Telephoto and Related Lenses for High Altitude Aerial Reconnaissance” (6017)
• “Design and Development of several types of 7-in f/2.5 lenses for night photography” (6018)
• “Design and development of an 100-in f/10 anastigmat for aerial reconnaissance at extreme Altitudes” (6019)
• “Apochromatic photographic aerial lenses and other optical instruments making use of synthetic fluorite” (6020)
• “Design and development of lenses for rectification of metrogon high obliques” (6021)
• “Development of seventeen unit power periscopes and rage finder for anti-submarine aerial patrol planes” (6022)
• “A practical application of the Schmidt camera to night photography” (6023)
• “A device for testing the flatness of film in the a-5 and a-7 magazines under service conditions” (6024)
• “Design and development of a 36-in f/8.0 telephoto for the K-18 camera” (6025)
• “Miscellaneous development work for other OSRD Projects” (6026)
• “Miscellaneous projects for instruction and laboratory purposes” (6027)
• “Miscellaneous projects partially completed” (6028)
• “Quantitative studies and observations of factor limiting resolution of aerial photographs” (6029)
• “A mirror method for harmonizing B-29 Guns and Sights” (4277)
• “The Optical Research Laboratory at Harvard” (4740)
• See also NDRC 16.1 Summary Report (Harrison and Baker, below)

Archival Collections

Records of the Office of Scientific Research and Development (1939-1950), Record Group 227, Series 10: Records of laboratories under contract with OSRD (1940-1946). National Archives and Records Administration, Waltham, MA.

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Baker, James. 1980. “Oral Histories: James Baker Interview by David DeVorkin.” American Institute of Physics. https://www.aip.org/history-programs/niels-bohr-library/oral-histories/32171.

Baker, James G. 1988. “Optics in the Early Forties at the Harvard College Observatory.” Optics News 14 (6): 14.

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McLeod, Brian, John Geary, Maureen Conroy, Daniel Fabricant, Mark Ordway, Andrew Szentgyorgyi, Stephen Amato, et al. 2015. “Megacam: A Wide-Field CCD Imager for the MMT and Magellan.” Publications of the Astronomical Society of the Pacific 127 (950): 366–82. https://doi.org/10.1086/680687.

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