$6 Macro Tilt Lens without glue or duct tape

Step 3 Determining Infinity Focus

Hold up the lens to your camera and point to something in the distance.  Move the lens in and out until the distant objects come into focus.  This lens came into focus around 10mm out from the camera flange.  Measure the distance from just inside the camera flange to the end of the lens and that's the length you need to cut your hose.