| This exceptional Celestron Axiom LX short focal length ultra wide field eyepiece uses seven optical elements for optimized performance across a very wide field of view. It’s a good choice for use with fast focal ratio refractors, providing a reasonably high magnification with a very wide field of view for observing globular clusters and the more compact open clusters and nebulas. With a usable eye relief of 13mm, the 7mm Axiom LX would normally somewhat vignette the field of view for eyeglass wearers. However, since the 82° field is so wide that you can’t see the full field without having to move your head from side to side to take it all in anyway, vignetting in the conventional sense is not a problem. There is a slight loss of contrast when compared to an eyepiece with fewer elements, due to the additional lenses needed to achieve the unique combination of very short focal length and very wide field. The loss is minimal though, on a par with the contrast loss in an eyepiece/Barlow combination with the same effective focal length. In the eyes of many observers, however, the “picture window on space" observing experience of its exceptionally wide field more than makes up for any slight contrast loss. You can use the calculator below to see just how wide the field will be with your particular telescope. For example, it will give you a 0.71° field (nearly one and a half lunar diameters) at 116x with a 4" f/8 refractor like the Takahashi TSA-102S triplet apo. The retractable eyeguard raises by turning the broad rubber grip ring around the eyepiece barrel clockwise and lowers by turning the ring back counterclockwise. The eyeguard mechanism may be a little stiff in operation the first time you raise it.
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