Off Axis Guiding is a form of auto-guiding in which use is made of the primary telescope and no separate guidescope.
To achieve this, a kind of mirror is placed in the primary light path of your telescope which deflects a piece of light towards the guide camera.
The purpose of autoguiding is to correct errors in the tracking, so that your shots remain sharp and stars are nicely round. But movements in your telescope can also cause stars to hit less beautifully and/or your images to be less sharp.
With a separate guidescope, not so much the primary telescope is corrected, but only on the basis of what the guidescope itself “sees”. So if movements take place in your telescope, the guidescope will not be able to see this. The consequence of this is that the stars are not optimal while you are using autoguiding.
The big advantage of OAG (“Off Axis Guiding”) is that elasticity and/or movements in the telescope are no longer a problem. After all, auto-guiding is applied from what the primary telescope itself sees and no longer from the separate guidescope.
SCT telescopes in particular benefit from Off Axis Guiding. Because it contains large heavy mirrors that are of course not stuck, it may be that some movement takes place here. With a refractor you have much less trouble with this. Nevertheless, OAG remains the best option for car guiding in all cases.
The configuration of OAG can sometimes be difficult, please contact us! We are happy to assist you in designing an OAG solution for your specific configuration!