The full-scale diagram below shows a converging lens and an object. Each principal focus is marked with an F: Draw two rays to find the position of the image.

The appeal of the super-oscillatory lens optical microscope described here is that it enables subwavelength imaging with, ... a SOL can—in principle—create a focus of any prescribed size 18.

We have found that a double focus lens can perform this function very efficiently, and the scheme lends itself to an effective demonstration of holography. Nature - Holography with a Double Focus ...

They come together at a point on the principal axis close principal axis An imaginary line which runs through the centre of a lens. called the principal focus F, (or focal point). The centre of ...