Two backup plates are usually recommended, one for the inside and one for the outside of the tube as a base for the focuser. We also have a flat base option for mounting the focuser on a flat surface. If your telescope tube has a slightly different radius than the focuser, you can add black foam weatherstripping tape under part of the focuser to block stray light while keeping a professional appearance. If your telescope tube has a slightly different radius than the focuser, you can add black foam weatherstripping tape under part of the focuser to block stray light while keeping a professional appearance. They give you the ability to collimate the focuser with respect to the optical light path.
Correct alignment is critical for optical quality.
The focuser will most likely have to be returned to us for installation of a Digital Read Out system. There is a small charge for any after-purchase installation or upgrade performed by us. The NGF-S is especially helpful when using a CCD camera. This focuser is placed on the visual back and does not require the mirror to be moved in order to achieve focus. Mirror movement in an SCT is what causes most of the image shift.