I have found that the two diagonals I own have a significant difference in that 90 degree angle.
You may ask "so what?" -but I have a set up that requires that I see the same guide star centered when swapping diags from an eyepiece to a guide camera.
A star centered in the camera can appear towards the outer
I could just swap the
A flip mirror might be the answer but I just do not have spacing for it. I could also experiment with shimming the mirror/prism but that would be a PITA.
Any ideas?