Glossary | Telescopes | General | Series | Omni XLT

The Celestron Omni telescopes are available as refractors and reflectors with mid-range apertures. The optics are especially characterised by their high-quality XLT coating, which is a byword for fewer reflections and high light transmission.

In combination with the CG-4 equatorial mount with ball-bearing worm gear drive and tubular steel tripod, Omni telescopes are very stable. They even enable a meaningful entry into astrophotography. For this, you will also need to purchase the optional motor drive, as listed in the recommended accessories. However, when starting out in astronomy, and for visual observation, the motor drive can be omitted initially.

A very important factor in evaluating the performance of telescopes is transmission, that is the proportion of incident light that arrives at the image plane.
The main characteristics of the StarBright®-XLT coating are as follows:

• Highly reflective multi-layer mirror coating: the mirror coatings consist of precisely applied layers of aluminium, quartz, titanium dioxide and more quartz. The reflectivity is constant across the spectrum, and the three layers of coating provide excellent protection against the ageing of the mirror surface.
• Corrector plate: crystal-clear glass instead of soda lime glass is used for the corrector plate in all Celestron Schmidt-Cassegrain optics with StarBright-XLT coating. Uncoated, this glass delivers approximately 90.5% transmission. Together with the StarBright®-XLT coating, its transmission reaches 97.4%!

The entire optical system consisting the corrector plate, mirror and lenses achieve a transmission maximum of 89% at 520 nanometres (where the dark-adjusted human eye has its highest light sensitivity). The average transmission over the entire visual spectrum from 400 to 750 nanometres is 83.5%.