As the centre mark on the primary mirrors of some telescopes makes it difficult to accurately determine the actual centre, or as the centre mark is not positioned centrally, a target disc has been developed for the OCAL collimators. This target disc allows you to see and assess the centre very clearly. Absolutely unambiguous!
Due to the manufacturing process, there may be slight variations in both the target discs and the threads of the OCALs. The target disc should be inserted into the thread of the OCAL from the front with minimal play. If the target disc fits too tightly in your setup, carefully sand the outer edge with sandpaper until the target disc can be inserted. Please handle with care; the ribs are very thin and may break if too much pressure is applied.
