| This 2” Celestron Axiom LX eyepiece is an excellent low power, wide field eyepiece that’s particularly well-matched to big Dobsonian scopes. While the longer focal length 31mm Axiom LX provides an even wider field of view with an f/4.5 scope, it also has a very large 6.9mm exit pupil, larger than many observers’ eyes can dilate. That effectively wastes some of the scope’s light gathering capacity, as some of the full light cone falls on the observer’s iris, rather than entering his or her eye. This 23mm Axiom LX, on the other hand, has a 5.1mm exit pupil with an f/4.5 scope. That’s an exit pupil more in line with the maximum dilated pupil of most observers’ eyes. With this 23mm, you get the full light-gathering your scope is capable of, while still keeping nearly the same wide “picture window on space" field of view as a longer focal length eyepiece. The six-lens design is primarily designed for no-holds-barred low power deep space use with scopes having focal ratios down to f/4. It is marvelous for open clusters, nebulas, and globular clusters with any scope, but is particularly effective with fast f/ratio reflectors. That being said, it must also be noted that its very wide field also makes it convenient for moderate power lunar and planetary observing with larger Dobsonians, as you have much longer to observe before the planet drifts out of the field and the scope has to be repositioned. With a usable eye relief of 17mm, the 23mm Axiom LX will provide nearly unvignetted views 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 in any case. 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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