The Vixen Optics #3907 Barlow Lens T is a 2x Barlow lens that inserts into 1.25" focusers or diagonals (when used with a diagonal, effective magnification is 3.3x instead of 2.0x).
This Barlow can be used conventionally for observing with a 1.25" eyepiece, but it can also be used as a SLR photo adapter. On the observing end of the unit there's a T-threading; simply attach a Vixen T-mount (listed here as accessories) to use this Barlow together with your SLR camera.
Magenta lens coating
Built-in T-mount adapter
In the Box
Vixen Optics 2x Barlow Lens (1.25") with Built-In T-Mount Adapter