Review on CNCOLETECH 18mm CO2 Laser Lens with 50.8mm / 2 Inch Focal Length - Ideal for CO2 Laser Engraving and Cutting Machines by Angela Rodriguez

Good news: After a quick inspection the lens was ok. It was a little cloudy but cleaned up well with alcohol. Bad news: I ordered a 50.8mm lens. The box I received said 50.8mm on the label but it was a 38mm lens. Luckily I saw a few reviews with similar issues so I measured the focal length before installing it in my laser cutter. I already had the 38mm lens that came with it, so I sent it back. Measuring the focal length of a converging lens (a lens that can focus a beam) is very simple: (1) Make two slits in a thin box, to be able to drag a ruler right through the box. Go outside and tilt it so the ruler doesn't cast a shadow on the box. (If you're doing this around noon, you can approach by placing the ruler straight up and down on a flat surface.) (2) Slide the lens up and down the ruler until you get the brightest/smallest spot of sunlight received on your box. .(3) Measure the distance between the lens and the box* - this is the focal length of the lens.* Don't just read the ruler to see where the lens is. You need to subtract where the ruler enters the box. ) (2) Slide the lens up and down on the ruler until you see the brightest/tiniest patch of sunlight on your box. . (3) Measure the distance between the lens and the box* - this is the focal length of the lens.* Don't just read the ruler to see where the lens is. You need to subtract where the ruler enters the box. ) (2) Slide the lens up and down on the ruler until you see the brightest/tiniest patch of sunlight on your box. .(3) Measure the distance between the lens and the box* - this is the focal length of the lens.* Don't just read the ruler to see where the lens is. You need to subtract where the ruler enters the box. until you see the brightest/tiniest patch of sunlight on your box. .(3) Measure the distance between the lens and the box* - this is the focal length of the lens.* Don't just read the ruler to see where the lens is. You need to subtract where the ruler enters the box. until you see the brightest/tiniest patch of sunlight on your box. .(3) Measure the distance between the lens and the box* - this is the focal length of the lens.* Don't just read the ruler to see where the lens is. You need to subtract where the ruler enters the box.