Review on Ajax Scientific Polished Spherical Bi Concave Science Education and Optics by Carlos Macy

Bought for a very specific purpose, to set the focus for a head worn digital eyepiece. The screen felt "too close" to the eye, and this lens mitigates that issue somewhat. However, I'd required an eyeliner makeover that I haven't completed yet, making it difficult to test in real-world conditions. However, the lens was within tolerance for the size described. I haven't measured the focal length, but as the description suggests, "it makes things smaller".