The ZWO off-axis guider is a special device that can be used instead of a guide scope. No need for a guide scope, more accurate guiding, and no need to worry about the guide scope shifting relative to the main scope while guiding, resulting in a streaky image.
How it works is simple: a prism inside the off-axis guider deflects some of the light coming into the camera and guides it out to the side. This produces a pattern for the guide from the same light that enters the camera's sensor. This light is picked up by the attached camera while driving the mechanism. All we need to do is set the desired object in the camera's viewfinder, check the focus and sharpness of the camera and autoguider, and also check that the autoguider is showing the star we want to follow.
The light path of the ZWO off-axis guider is 16.5 mm.Threads M42 and M48 are provided for the scope and camera, respectively, and the necessary adapters are included in the package. The guiding camera can be connected to the off-axis guider via a 1.25" cable or T2 thread.