Baader's M48 spacer ring for MPCC III Coma Corrector / Protective Canon EOS T-Ring is an important new addition that allows you to use the full 48mm aperture of these accessories as opposed to the restricted 42mm T2 thread aperture that can cause vignetting.
Baader's MPCC III Coma Corrector # 2458400 allows you to attach a camera using either M48 or T2 threads. If you plan to use the M48 connection, then you require this adapter to maintain the correct spacing from the corrector to the camera's focal plane. The same is the case if you attach your camera to Baader's Protective T Ring for Canon EOS cameras # 2958550. Note that this adapter is not required if you intend to use the T2 thread on either of these items.
This adapter features an M48 female thread on one side and a male dovetail ring on the other side.
Manufacturer part #: MPCC-SPCR or 2458405