An ideal piece for afocal and projection astrophotography techniques, the Alpine Astronomical Baader T-2 / SP54a Expanding DT-Adapter II is used to attach any of Baader's M54 threaded HDT rings onto an eyepiece that has male T-threads. If you want to use one of their Hyperion or Morpheus eyepieces, you need this adapter with another optional T-ring to attach the eyepiece to the Baader Afocal Digital Projection System (ADPS).