Dioptra Island (Bulgarian: остров Диоптра, romanized: ostrov Dioptra, IPA: [ˈɔstrov diˈɔptrɐ]) is the conspicuous 290 m long in east-west direction and 45 m wide rocky island off the northwest extremity of Low Island in the South Shetland Islands, and separated from Beslen Island on the southeast by a passage narrowing to 21 m at points. Its surface area is 0.92 ha.

The feature is named after the classical surveying instrument dioptra, and in association with other names in the area deriving from the early development or use of geodetic instruments and methods.

Dioptra Island is located at 63°13′14″S 62°11′11″W / 63.22056°S 62.18639°W / -63.22056; -62.18639, which is 6.09 km northwest of Venev Point and 1.57 km northeast of Cape Wallace. British mapping in 2009.

• List of Antarctic and subantarctic islands

• South Shetland Islands: Smith and Low Islands. Scale 1:150000 topographic map No. 13677. British Antarctic Survey, 2009
• Antarctic Digital Database (ADD). Scale 1:250000 topographic map of Antarctica. Scientific Committee on Antarctic Research (SCAR). Since 1993, regularly upgraded and updated

• Bulgarian Antarctic Gazetteer. Antarctic Place-names Commission. (details in Bulgarian, basic data in English)

• Dioptra Island. Adjusted Copernix satellite image

This article includes information from the Antarctic Place-names Commission of Bulgaria which is used with permission.