Thank you for choosing the OGMA Off-Axis Guider (OAG). An OAG is a critical tool for astrophotography, enabling you to guide your mount using the same optical path as your primary imaging camera. Instead of using a separate guide scope, the OAG diverts a small portion of the light through a pick-off prism into a guide camera, resulting in more accurate tracking and eliminating common issues like differential flexure.
For optimal performance, it is essential to maintain the same backfocus distance between the imaging and guiding cameras. Matching these distances ensures that both cameras can reach focus without strain or compromise to your optical train.
A good focusing process involves two steps:
First, achieve perfect focus with your primary imaging camera.
Then, adjust the guide camera position along its helical until the guide stars appear sharp.
Never adjust the focus of your primary imaging camera after the guide camera is focused—always focus the primary camera first.
Because the OAG uses only a small section of the light cone, proper positioning of the prism is crucial and must be adjusted carefully to ensure optimal guiding performance:
Ideal position: The prism is inserted close enough to the primary imaging sensor to capture guide stars while staying clear of the imaging sensor's field of view.
Too far from the center of the light path: The prism may capture distorted stars with comma near the edge.
Too close to the sensor: The prism may cast a shadow on the primary imaging sensor.
The OGMA OAG allows you to fine-tune the prism height to achieve this balance and maximize performance with your setup.
In the following sections, this manual will guide you step-by-step through the installation process to achieve optimal results.