This is a complete housing without the SIPS optic. The housing can be used for astronomers that have more than 1 telescope and want to use the SIPS on multiple scopes. You can simply unscrew the optics from the SIPS unit on one scope and screw in the optics into this housing on another scope. If you want to use the SIPS unit on more than 1 telescope, this will allow you to conveniently and efficiently utilize the SIPS unit on both scopes without having to purchase 2 complete SIPS units. Once the optics are installed in the housing there is no need to “re-tune” the optics.