ToupTek OAG-L Off-Axis Guider

The ToupTek OAG-L is an off-axis guider 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. That removes flexure between guide scope and telescope, which is what spoils long exposures at long focal lengths.

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

It works with standard guide cameras. If you image at long focal lengths or through narrowband filters, the OAG-X has a larger prism but needs an extended-nose guide camera.

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, and the clear opening through the body is 54 mm.