60 mini black wedding favor soaps From my shower to yours ...- tradurra dish soap ,2. Handmade soap will last a long time if kept dry between uses. 3. Please use a draining soap dish and keep it away from direct streams of water. 4. Since our products are truly all natural and we do not use any unnatural preservatives, our products do have a shelf life, typically 6 months to 1 year.Optical Power (Diopter) to Focal Length Converter ...The optical power (dioptric power or refractive power) D of a lens or another optical system is the degree to which the system converges or diverges light. It is calculated as follows: D = 1/f. where f is the focal distance of the lens. Larger focal length lenses have less optical power. In SI, optical power is measured in reciprocal meter (m⁻¹).