Assertion: mm eyepiece | /r/ObjectUse | used in a two-inch focuser
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Source sentences:
text: A 40 mm eyepiece will give a nice low magnification in an f/10 refractor or in a Schmidt-Cassegrain, but it must be have a two-inch barrel and be used in a two-inch focuser, if it is to give a wide field of view, as well.