Azadeh Alijani - Department of Mathematics, Faculty of Sciences, Vali-e-Asr University of Rafsanjan, P.O. Box ۷۷۱۹۷۵۸۴۵۷, Rafsanjan, Iran.

Hilbert frames theory have been extended to frames in Hilbert $C^*$-modules. The paper introduces equivalent $*$-frames and presents ordinary duals of a constructed $*$-frame by an adjointable and invertible operator. Also, some necessary and sufficient conditions are studied such that $*$-frames and ordinary duals or operator duals of another $*$-frames are equivalent under these conditions. We obtain a $*$-frame by an orthogonal projection and a given $*$-frame, characterize its duals, and give a bilateral condition for commutating frame operator of a primary  $*$-frame and an orthogonal projection. At the end of paper, pre-frame operator of a dual frame is computed by pre-frame operator of a general  $*$-frame and an orthogonal projection.

Dual frame, Equivalent $*$-frame, Frame operator, $*$-frame, Operator dual frame