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Deutsch: Afokales System / Español: Sistema afocal / Português: Sistema afocal / Français: Système afocal / Italiano: Sistema afocale

An afocal system is an optical system that produces no net convergence or divergence of a beam, essentially outputting collimated light. In the space industry, afocal systems are particularly useful in telescopes, cameras, and other imaging technologies used on satellites and spacecraft.


An afocal system typically consists of two or more lenses or mirrors designed to produce an output beam that is parallel, or collimated. This means that the exit rays are parallel to the axis of the system, regardless of the angle at which the input rays enter. The main characteristic of an afocal system is that it has an infinite focal length, which means it does not focus light to a point but rather maintains the direction of light rays across the system.

In the context of the space industry, afocal systems are employed in several critical applications. They are integral to the design of space telescopes, which require precise control over light to effectively capture distant cosmic objects without introducing focal variation that could blur the images. Afocal systems are also used in coupling optics between different systems, where maintaining beam direction and integrity is crucial.

Moreover, afocal attachments can be used with cameras to increase the field of view, which is essential for wide-area surveillance from satellites or for capturing large celestial phenomena in astronomy. These systems adjust the focal properties of standard optical systems to suit specific requirements, such as imaging wide swaths of Earth’s surface from orbit.

Application Areas

Afocal systems find several applications in space technology:

  1. Space Telescopes: Enhancing the capability of telescopes to observe distant stars, galaxies, and other celestial bodies without the distortions that typically come from focusing systems.
  2. Satellite Imaging: Used in Earth observation satellites to provide broad, undistorted views of the Earth’s surface for environmental monitoring, mapping, and surveillance.
  3. Optical Communications: Employed in the optical communication systems used for high-speed data transfer between satellites and from satellites to ground stations, where maintaining collimated light beams is essential for efficient signal transmission.

Well-Known Examples

Notable examples of afocal systems in the space industry include:

  • The Hubble Space Telescope, which uses an afocal system as part of its complex arrangement of mirrors to deliver clear and highly detailed images of space.
  • Many modern spy satellites and Earth observation systems, which utilize afocal optics to maximize their surveillance capabilities over wide areas.

Treatment and Risks

While afocal systems offer significant advantages, their design and implementation in space environments come with challenges. Precision in manufacturing and alignment is crucial to avoid aberrations that could degrade image quality. The systems must also be robust to withstand the launch environment and long-term exposure to space conditions, including radiation and extreme temperatures.

Additionally, the complexity of afocal optical systems can increase the cost and time required for development and testing. Ensuring that these systems perform reliably over the lifespan of a spacecraft or satellite is essential to justify the investment.


The afocal system is a pivotal component in the optical and imaging technologies used in the space industry. Its ability to produce collimated light makes it ideal for applications ranging from high-resolution telescopic imaging to broad-area satellite surveillance. Despite the technical and cost challenges associated with their development, afocal systems continue to be integral to advancements in space exploration and observation technologies.


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