Optical Device and Prism Module Thereof

An optical device includes an objective module, a prism module and an ocular module. The prism module includes a first prism, a second prism and a first coating. The prism module is disposed between the objective module and the ocular module. A first light beam emitted by an object sequentially passes through the objective module, the prism module and the ocular module. Central axes of the objective module and the ocular module are in parallel without overlapping.