Celestron 4SE Image Orientation, 2a - Actual image orientation as seen with the unaided eye

A telescope is an instrument that collects and focuses light. The nature of the optical design determines how the light is focused. Some telescopes, known as refractors, use lenses. Other telescopes, known as reflectors, use mirrors. The Maksutov-Cassegrain optical system uses a combination of mirrors and lenses and is referred to as a compound or catadioptric telescope. This unique design offers large-diameter optics while maintaining very short tube lengths, making them extremely portable. The Maksutov-Cassegrain system consists of a corrector plate, a spherical primary mirror, and a secondary mirror spot. Once light rays enter the optical system, they travel the length of the optical tube three times.

Figure 5-1

A cutaway view of the light path of the Maksutov-Cassegrain optical design

The optics of the NexStar have enhanced multi-layer coatings on the primary and secondary mirrors for increased reflectivity and a multi coated corrector for the finest anti-reflection characteristics.

Inside the optical tube, a black tube extends out from the center hole in the primary mirror. This is the primary baffle tube and it prevents stray light from passing through to the eyepiece or camera.

Image Orientation

The image orientation changes depending on how the eyepiece is inserted into the telescope. The NexStar uses three reflective surfaces to bounce the light to the eyepiece. This produces an image that is right-side-up, but reversed from left-to-right (i.e., reversed). This is normal for the Maksutov-Cassegrain design.

Fig 5-2a - Actual image

orientation as seen with the

unaided eye

Fig 5-2b - Reversed from left to

right, as viewed through the

eyepiece

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