This 1.25″ astigmatism corrector drops in the ONAG XM and SC guider port focuser draw tube and it is secured with two #4-40 set screws.
When in place the corrector minimizes the ONAG dichroic beam splitter induced astigmatism providing diffraction limited guide stars.
The corrector is useful for imaging in NIR, while guiding or imaging in visible from the ONAG imager port (IP). It is also recommended for fast scopes with f/#<6 and/or large central obstructions (>40%). This corrector reduces the ONAG guider back focus distance by 3mm.
When used with the continuous real time auto focus softwareFocusLock(FL) the corrector can be rotated to dial back some controlled level of astigmatism.
Consult theONAG user manual (version 6 and higher) for installation and further information.