A system can include an optical device and an accessory device. The optical device can include a housing, an objective lens at a first end of the housing and supported by the housing, an ocular lens at a second end of the housing and supported by the housing, and an optical path defined from the objective lens through the housing to the ocular lens, and a display device supported by the housing proximate the second end of the housing. The display device can include a display, hardware logic circuitry to process display data and to display the display data on the display, an input port, and a display holder to position the display in the optical path in the presence of a signal from the accessory device and to position the display out of the optical path in the absence of a signal from the accessory device.