Celestron Omni Series 1.25 inch - 9mm

The short focal length 9 mm omni eyepiece is a Plössl eyepiece with a four-lens, symmetrical design
    Particularly interesting for compact deep sky objects such as planetary nebulae or globular clusters
    Blackened lens edges suppress internal reflections and increase contrast,
    the multi-layer coating on each lens surface allows maximum contrast and light transmission,
    In addition, each eyepiece is anodized twice to suppress reflections on the housing - with many other manufacturers you will find reflective surfaces instead.
    You can screw any 1 1/4" Celestron eyepiece filter into the thread of the eyepiece sleeve.

Many inexpensive entry-level telescopes come with cheap eyepieces, which are sufficient for a first look through the telescope, but soon leave you wishing for something better - a small field of view or an uncomfortably short eye relief makes observing difficult. Simple eyepiece designs based on Kellner, Ramsden or Huygens (recognizable by abbreviations such as K, H, or SR) are no longer appropriate today - even if they are often touted as "high-performance eyepieces".

With the Omni eyepieces, Celestron offers an inexpensive alternative. These are Plössl eyepieces with a four-lens, symmetrical structure. Blackened lens edges prevent reflections inside the eyepieces and increase contrast, the multi-layer coating on each lens allows maximum contrast and light transmission. Additionally, each case is anodized twice to prevent reflections - with other manufacturers you will find reflective surfaces instead.

The eyepieces are pleasantly light and offer a good field of view - although it is smaller than the much more expensive wide-angle eyepieces, there is no longer any annoying tunnel vision. You can screw in any 1.25" filter using the filter thread integrated into the eyepiece sleeve, for example to attenuate the light when observing the moon or to use nebula filters for deep sky observation.

With a Barlow lens you can
double the magnification.

A retaining groove in the socket prevents the eyepieces from slipping out of the focuser and falling to the floor when you swivel the telescope and the clamping screw may be loose.
The Plössl construction method

The Plössl eyepieces are among the first modern eyepiece designs and go back to the Austrian optician Simon Plössl, who developed them in 1860. It was only in the 1980s that the design became established because it can be manufactured in good quality using modern techniques and is far superior to older eyepiece designs. With an apparent field of view of around 50°, they are good, versatile eyepieces that can accompany you for many years. If you are looking for inexpensive eyepieces that are worth the money, the Celestron Omni eyepieces are a good choice.

Only at focal lengths of less than about 10mm does the eye relief become somewhat small due to the design - people who wear glasses in particular can use the longer focal length lenses in conjunction with the 2x Barlow lens. The Barlow doubles the magnification, while the pleasant viewing behavior of the longer focal length eyepieces is not changed.

The 9mm eyepiece

The 9mm model provides higher magnification on most telescopes and is particularly interesting for compact deep sky objects such as planetary nebulae or globular clusters. With the optionally available Omni 2x Barlow lens, you can achieve the higher magnifications required for planets, especially on short focal length telescopes, without having to forego the eye relief of 6mm. However, this eye relief is no longer suitable for use with glasses. Observers who are only nearsighted or farsighted can use the eyepiece without glasses; If the glasses compensate for other visual defects such as astigmatism, a longer focal length eyepiece with a corresponding Barlow lens or a more expensive eyepiece design with a greater eye relief makes sense.

When using a Barlow, you should not magnify too high - the maximum sensible magnification is approximately twice the lens aperture in mm.
Manufacturer Celestron
Item number (#) 810234
EAN Code 4047825005854
Net weight (kg) 0.07
Technical data
Focal length 9 mm (0.35 in)
Field of view 50°
Eye relief (mm) 6 mm (0.24 in)
Plug size (inch) 1¼"
Eyepiece properties
Number of lens elements 4
Connections
Filter thread Yes