The Cassegrain design is a type of telescope that uses a combination of mirrors to focus light. It features a large primary mirror that collects light and reflects it to a smaller secondary mirror. This secondary mirror then directs the light back through a hole in the primary mirror, allowing for a compact design. This design is popular in both amateur and professional telescopes due to its ability to produce high-quality images while maintaining a shorter overall length. The Cassegrain telescope is often used in astronomy and other fields that require precise observations of distant objects.