Abstract: An apparatus is herein provided for use in the adjustment of an ocular mechanism within an optical instrument, such apparatus including a base with an aperture at least partially surrounded by perimetrically conforming upstanding member. The apparatus further includes a hollow drawtube which holds the ocular mechanism and substantially matingly conforms to both the aperture and the upstanding member to provide for controlled passage of the drawtube through the aperture. The drawtube is held by a radially adjustable control shaft and a plurality of spaced bearings. The control shaft is selectively placed in rotating frictional engagement with the drawtube by linear, radial translation of the shaft.