Techniques are disclosed for creating optical systems and devices that enable a mobile device (e.g., smartphone or other mobile phone, personal media player, and/or other personal electronic device) to be coupled with an optical device (e.g., a riflescope, spotting scope, etc.) such that information shown on the display of the mobile device is viewable to a user looking into the eyepiece of the optical device. Additionally or alternatively, an image from the optical device can be communicated to the mobile device. A modular design can utilize an apparatus configured to encase a mobile device, which can be coupled with the optical device via and optical and/or electrical interface.