Lumicon 2 Inch Prime Focus Camera AdapterLumicon 2 Inch Prime Focus Camera Adapter drops into a 2 telescope eyepiece holder and presents male T threads (42mm x 0. 75mm) for T ring attachment. Lumicon 2 Inch Prime Focus Camera Adapter Lumicon 2 Inch Prime Focus Camera Adapter drops into a 2 telescope eyepiece holder and presents male T threads (42mm x 0. 75mm) for T ring attachment. For prime focus photography where back focus is not critical, and for variable focal reduction on Lumicons