Celestron Omni Series 1.25 inch - 40mm

The long focal length 40 mm omni eyepiece is a Plössl eyepiece with a four-lens, symmetrical design.
    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 40mm eyepiece

The 40mm Omni eyepiece is the longest focal length model in the Omni range and offers the lowest magnification. It is the only one that has a smaller field of view than the other models, as the maximum real field of view that is possible with 1.25" eyepieces is already achieved at a focal length of approx. 32mm. If it is just about field of view, the 32mm eyepiece is the one better choice. The big advantage of the 40mm eyepiece is that the image is brighter: the more you magnify, the darker the image becomes For example, you can see faint nebulae better than with a 32mm eyepiece, while overlooking the same real section of the sky.
 
Manufacturer Celestron
Item number (#) 810246
EAN Code 4047825005793
Net weight (kg) 0.20
Technical data
Focal length 40 mm (1.57 in)
Field of view 43°
Eye relief (mm) 31 mm (1.22 in)
Plug size (inch) 1¼"
Eyepiece properties
Number of lens elements 4
Connections
Filter thread Yes