In some applications, it may be desirable to position multiple photodetectors at precise locations on a curved focal surface defined by an optical system. To achieve this positioning, the photodetectors may be mounted at desired locations on a flexible substrate that is in a flat configuration. The flexible substrate with mounted photodetectors can then be shaped to substantially conform to the shape of the curved focal surface. This shaping can be accomplished by clamping the flexible substrate between at least two clamping pieces. The curved flexible substrate clamped between the at least two clamping pieces can be positioned relative to the optical system such that the photodetectors are positioned at desired three-dimensional locations on the curved focal surface.