ZWO Off-Axis Guider

ZWO Off-Axis Guider gives a guide camera its own small optical path so the mount can correct tracking during long exposures. It is simple, light, and effective on wide-field refractors and camera-lens rigs.

The limitation is differential flexure. As focal length rises, or as the main telescope uses a moving mirror, an off-axis guider usually gives more trustworthy corrections.