The solar image is not darker with reduced aperture as we allow for this in the coating density. Reduced center aperture is used for refractors. If full aperture is still preferred, it can be stopped down using a simple mask as conditions dictate. The filter is mounted in a polished aluminum cell designed to fit over the end of the tube. Telescope manufacturers often make changes to the tube size, so the OD measurement is important.
All filters including reduced aperture are ready to use.
Only if you plan to use a film slower than 100 speed. Polymer Plus and glass filters have highly reflective coatings that can cause internal reflections between the filter and camera lens since the filter and lens are in close proximity. This problem is less likely to occur with telescopes, however, mounted telescope filters can be tilted slightly to move any internal reflections off the central axis and out of view. Items listed below will be dropped shipped direct from factory. All filters are mounted in a polished aluminum cell.