Sky-Watcher 200 mm Secondary Mirror for Newtonian Telescopes 200/1000 and 200/1200

Sky-Watcher 200 mm Secondary Mirror for Newtonian Telescopes 200/1000 and 200/1200

The secondary mirror is one of the key optical components in a Newtonian reflector. Although it is considerably smaller than the primary parabolic mirror, its quality and correct alignment have a direct effect on the sharpness and contrast of the final image. This replacement secondary mirror from Sky-Watcher is manufactured from high-quality optical glass with a precisely ground elliptical face and a reflective coating that ensures high reflectivity across the entire visible spectrum.

When Should the Secondary Mirror Be Replaced?

There are several reasons why a secondary mirror may need to be replaced. The most common is mechanical damage - cracking, heavy scratching or flaking of the reflective coating, which can occur after a drop or improper cleaning. The reflective coating also has a limited lifespan and degrades over time, which manifests as reduced image brightness and contrast. Replacing the secondary mirror with a new, undamaged unit is in such cases the simplest and most effective solution.

Another reason may be a deliberate upgrade of the optical system. Replacing an older secondary mirror with one featuring a better coating or a more accurately ground surface can noticeably improve the performance of a telescope, particularly in older instruments with original lower-quality mirrors.

Compatibility - Which Telescopes Is This Mirror Suitable For?

This secondary mirror with dimensions of 73 x 51 mm is primarily intended for Newtonian telescopes with a 200 mm primary mirror diameter and a focal length of 1000 mm - that is, for the 200/1000 (f/5) tube. It can also be used in the 200/1200 (f/6) telescope, although a slightly smaller secondary mirror will be a better match for that instrument - see [SW-5512]. The choice of the correct secondary mirror size depends on the focal ratio of the telescope and the intended use: for visual observing with smaller eyepieces a smaller secondary is sufficient, while for astrophotography with a dedicated camera or DSLR a larger secondary is preferable to ensure even illumination across the full sensor area.

As a general rule, the slower the telescope (the higher the f/ number), the smaller the secondary mirror needed to fully illuminate the field of view. Conversely, in fast Newtonians such as f/5, a larger secondary mirror is justified to ensure that the sensor or eyepiece is evenly illuminated right to the edges of the field.

Installation and Collimation

The secondary mirror is mounted in a holder (spider) positioned inside the tube. After replacing the mirror, the entire optical system must be collimated - meaning the secondary and primary mirrors must be correctly aligned relative to the tube axis and the focuser. Collimation of a Newtonian reflector is a standard procedure that any user can carry out with the help of a collimation eyepiece or laser collimator. A correctly collimated instrument with a quality secondary mirror rewards the observer with sharp, detailed images of stars and planetary surfaces, free from blurring or asymmetric diffraction patterns.

Technical Specifications