Specification:1) Diameter: 42mm.2) Focal length: 24/28/35/40/50/60/70/80mm.3) Thickness: 2mm.4) Grain pitch: 0.3mm.5) Shape: Round.6) Material: acrylic.7) Production process: cold forming.8) Transmittance: 93%.9) Use temperature: -40 degrees -80 degrees.Please note:1) Fresnel lenses are concentric circles on the front and smooth surfaces on the back, with a regular thickness of 2mm and edges as thick as the center (not convex anywhere, not convex lenses!!).2) Fresnel lens and convex lens are the same in function, but the two shapes are completely different, please pay attention to the distinction.Note:1. The real color of the item may be slightly different from the pictures shown on website caused by many factors such as brightness of your monitor and light brightness.2. Please allow slight manual measurement deviation for the data.