The beamsplitter in Michelson interferometer influenced the light, going through respectively being reflected by 90°.
Has somebody of you ever see what shape has the spot from a laser source on the observation screen if one of the mirrors is not installed?
Edit: There is a comment:
I have not and I no longer have access to a Michelson interferometer. If you have observed fringes then they might be due to the multiple reflections from the top and bottom of the beam splitter and the compensator.