Idea of Focal Length Icon
There is a single cone shape lying on it's side with the tip to the left and it's bottom face visible on the right side, beaming off the top and bottom of the bottom face is two diagonal lines, and halfway through each diagonal line is a curved line connecting them.
This Focal Length icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 6,100 icons, all in the same style and quality.