Celestron X-Cel LX 12mm vs 18mm: Which Focal Length to Buy
By TelescopesPlus - The #1 Online Store for Telescopes and Accessories | Published: 2026-11-03
Category: Koopgidsen
Compare the Celestron X-Cel LX 12mm and 18mm eyepieces by magnification, eye relief, and target, with clear rules for which focal length to buy first.
Quick answer
Buy the Celestron X-CEL LX 12mm (93424) if your main goal is planetary and lunar detail at higher power; buy the 18mm (93425) if you want a wider, more forgiving view for deep-sky objects and easier eye placement. If you can only buy one and your scope has a short focal length, start with the 18mm.
Why 6mm of focal length changes the view
The 12mm and 18mm share the same 60-degree apparent field and six fully multi-coated elements, so the difference you feel at the eyepiece is magnification and exit pupil, not optical design. A shorter focal length magnifies more but produces a smaller exit pupil, which dims extended objects and makes eye placement less forgiving. The 18mm gives a brighter image and a larger exit pupil, which helps when you are hunting faint nebulae or when your mount is not perfectly steady.
The magnification depends on your telescope, not the eyepiece alone
Magnification equals telescope focal length divided by eyepiece focal length. On a 650mm short-tube refractor, the 12mm gives about 54x and the 18mm about 36x; on a 1200mm Dobsonian, they give about 100x and 67x. That means the same eyepiece can be a low-power sweeper on one scope and a planetary workhorse on another. Check your scope's focal length before choosing, because the 12mm may be too low power for planets on a short scope or too high power for steady seeing on a long one.
Eye relief and comfort are not listed, so plan around that gap
The catalog does not publish eye relief for either eyepiece, so do not assume the 12mm will be comfortable with glasses just because the 18mm is. As a rule, shorter focal lengths in a given line tend to have tighter eye relief, but without a published figure you should treat comfort as an open question and buy from a store that allows returns. If you observe with glasses, the 18mm is the safer first choice.
Decision rules for choosing between the 12mm and 18mm
- If planets and the Moon are your priority: Choose the 12mm when your telescope focal length is 900mm or more, where it delivers roughly 75x or higher and puts planetary detail within reach. Check your scope's focal length first; on a 650mm scope the 12mm gives only about 54x, which is not a planetary power.
- If deep-sky objects and easy viewing are your priority: Choose the 18mm for a brighter exit pupil and a wider true field, which makes star clusters, nebulae, and star-hopping more forgiving.
- If you wear glasses while observing: Start with the 18mm, since eye relief is not published for either model and the longer focal length is the safer bet for comfortable eye placement. Confirm the return policy before ordering, because comfort cannot be judged from the catalog alone.
- If you are buying only one eyepiece: Pick the focal length that fills the biggest gap in your current set; if you have no other eyepieces, the 18mm is the more versatile first step.
Product facts
- Celestron X-CEL LX 12mm Telescope Eyepiece - 93424: All six optical elements are fully multi-coated, with a 60-degree apparent field. The wide field keeps the 12mm from feeling like a narrow peephole when you push magnification on planets.
Celestron X-CEL LX 12mm Telescope Eyepiece - 93424 - Celestron X-CEL LX 18mm Telescope Eyepiece - 93425: The 18mm uses the same six-element, fully multi-coated design and 60-degree field. You get the same optical formula and viewing comfort as the 12mm, just at lower power and with a brighter exit pupil.
Celestron X-CEL LX 18mm Telescope Eyepiece - 93425
Who should buy which
Best for
- Owners of 900mm-and-longer telescopes who want a planetary and lunar eyepiece
- Observers building a small set who want a higher-power companion to a low-power eyepiece
Not for
- Short-tube refractor owners who need low power for wide-field scanning
- Glasses wearers who cannot try the eyepiece before buying and need guaranteed eye relief
