138mm Round Drop-In +1 Diopter Close Up Lens. Close-Up Lenses (Diopters) are used when you need to get really close-up images of small objects. They are lightweight and quick to use with standard matte boxes and filter holders. TThey are available in five strengths, +1/4, +1/2, +1, +2 and +3. Use the +1/4 when you need to get just a tiny bit closer. The +1 gets you close . . . the +3 gets you VERY close. Lindsey Optics Brilliant Diopters are made from the finest optical glass. They feature our rock hard, multi-layer BROADBAND anti-reflective coating. This measurably reduces light loss and flare. Contrast, color saturation and image quality are preserved.