In the first step measure the diameter of the lens and multiply by 3.14... (number Pi) to calculate the width of the cut. Then measure the length of the lens including the sunshade, teleconverter, extension ring and camera to get the length of the blank. For both measurements, round up generously so that it is not too tight. Now the fabric can be cut. Either freehand or with a previously made template of paper or cardboard. The two longitudinal ends of the resulting square must now only be connected to the lens clamp or to the height of the tripod connection and the cover for your lens is ready. The camera is also protected underneath. You can join the two ends together with a seam or with a fabric glue. In my case, the sewing machine connected the two ends within a minute with a nice seam. For my big lens I sewed in a zipper to vary the position of the tripod clamp (because I am often on the road without a lens hood).