Use the Baader Off-Axis Guider to directly connect your guide camera to their FlipMirror II mirror diagonal, so you can be sure your tracking stays accurate during your astrophotography sessions. The way the prism is located in the diagonal allows it to operate completely independent of the mirror position, enabling your guide camera to continue to make corrections whether you are looking through an eyepiece on the top of the diagonal or allowing the light to pass straight through to your imaging system.
Since it was designed specifically for the FlipMirror II diagonal, installing it produces a direct and solid connection without interfering with the operation of the diagonal or covering a portion of your camera's sensor. The distance between the guider's prism and the optical axis of the diagonal is 17.5mm without the included 4mm spacer, and if you need additional space for the prism to clear a larger imaging sensor you can install the spacer to lower it—but doing this will reduce the amount of usable light entering the prism and thus into your guide camera.