Image-stabilization systems are used in many applications, ranging from astronomical imaging to optical communications systems. Despite the differences in application, many tip-tilt systems have a great deal in common because they make use of a wavefront sensor, a controller, and a wavefront compensator. The differences between the systems are often in the selection of the individual components used to make up the final system.
Previous chapters identified the function of the components and demonstrated how they are used together. This chapter provides an overview of several prominent observatory and telescope projects that use image-stabilization systems. The image-stabilization instrumentation identified here is often included as part of large adaptive optics and long-baseline interferometric systems. The project-specific material presented here was taken from the literature and publications about the projects. References are provided so readers can follow up on projects that they find particularly interesting.
7.2 Astronomical Imaging Tip-Tilt Systems
Imaging through atmospheric turbulence has provided a number of challenges for astronomical observers. As the first large telescopes became available in the first quarter of the 20th century, observers using long exposures on photographic plates faced significant challenges in keeping the stellar images in fixed position on spectroscope slits or on imaging plates. On many of the early large telescopes, the position of the star on the photographic plate was controlled by visual guiding; that is, the observer watched the position of a star in a high magnification eyepiece attached to the plate holder and adjusted orthogonal positioners to keep the star fixed in a high-magnification eyepiece, and thus on the plate. As observations could literally take all night, this was not a great assignment.
As electronic imagers became available in the mid-1930s, the first autoguiding systems began to be developed. These early autoguiders evolved into the astronomical wavefront correction systems we see today. The first was proposed by Horace Babcock (1953) at the Mount Wilson Observatory.