The Vixen Flip Mirror System has a conventional 1.25" eyepiece adapter in the vertical position, and a second straight-through attachment which lets you directly screw upon an SLR camera T-mount.  Also included in the package which adapts the straight-through path to 1.25", so that you can have an eyepiece on both sides or you can shoot perform eyepiece projection adapter with the #3931 SX Camera Adapter.

The flip mirror allows speedy switching between viewing from the vertical position or allowing the light to pass straight through the flip mirror to your SLR camera (with or without an eyepiece in the path) attached to the rear.  When using the flip mirror for photography, users commonly insert illuminated reticle eyepieces in the vertical position so they can periodically flip the mirror to check that the image isn't drifting during the exposure, and correct for such drift if necessary.