Image Processing Reference
In-Depth Information
Chapter 7
Image-Stabilization Systems
7.1 Introduction
Image-stabilization systems are used in many applications, ranging from astronom-
ical imaging to optical communications systems. Despite the differences in appli-
cation, 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 be-
tween 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 promi-
nent 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 20 th century, observers using long exposures on photographic plates
faced significant challenges in keeping the stellar images in fixed position on spec-
troscope slits or on imaging plates. On many of the early large telescopes, the posi-
tion 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 at-
tached 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 liter-
ally 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 astronom-
ical wavefront correction systems we see today. The first was proposed by Horace
Babcock (1953) at the Mount Wilson Observatory. This system was first used on
the 60-in. telescope and was more than just a tip-tilt system, since it also corrected
Search WWH ::

Custom Search