ZWO off-axis guiders offer the best solution for guiding as they eliminate the problem of the differential flexure. This effect can arise when a guiding scope is used: while a camera is capturing an image with the main telescope, the guiding scope can flex toa different amount causing a guiding error.
An off-axis guider is installed on the main telescope before the camera so this problem does not occur as the guiding and imaging telescope are actually the same instrument. The off-axis guide uses a prism that deviates part of the light from the main telescope and redirects it to the guiding camera. However, it will not block any light to the sensor or create any shadow if oriented on the right way.
Available in different sizes to suit all ZWO cameras.