ToupTek OAG-X Off-Axis Guider

The ToupTek OAG-X is the larger of ToupTek’s two off-axis guiders, for ATR and other cooled cameras. A prism picks light from the edge of the telescope’s field and sends it to a guide camera, so you guide through the main telescope instead of a separate guide scope.

It adds 17.5 mm to the optical train. The prism is 14 × 10 mm, with an effective aperture of 14 × 7 mm, and it’s made in M48, M54 and M68 versions to match the threads in your optical train.

OAG-X or OAG-L

The OAG-X’s prism is 40% larger, so it collects more light and finds guide stars more easily, which counts at long focal lengths and with narrowband filters. ToupTek says it works only with the Extended versions of its GPM and G3M guide cameras, not the standard versions or other planetary cameras. The OAG-L works with standard guide cameras and is the simpler choice for shorter focal lengths.

Spacing with ATR cameras

The OAG comes with a 20 mm extender. With an ATR camera’s 17.5 mm back focus, the extender and the OAG’s own 17.5 mm, the sensor sits 55 mm behind the telescope adapter: the spacing most flatteners and reducers need. The camera side screws to the extender, a ToupTek filter wheel or the M54 filter drawer.