The C91003 is the Pentax Close-Up Lens #1. It is the most powerful close-up adapter for inspecting images to very small detail. The #1 lens changes the focal length of the camera lens by 1000 millimeters. In effect it makes the object much larger and much more detail is evident for critical evaluation. This adapter is for 40.5mm filter diameter lenses.
In the Box
Pentax C91003 #1 Close-Up Lens Adapter for 40.5mm Filter Lenses increases Focal Length by 1000mm