Let is say you have two eyepieces in your accessory case, a 10 mm and a 25 mm. Add a Celestron Omni 2X Barlow Lens to the mix, and now you have four magnifications to choose from. Combining this lens with the 25 mm provides double the magnification, or the equivalent of a 12.5 mm eyepiece, while the 10 mm gives you the power of a 5 mm eyepiece.
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