The Monocle
There's something about the monocle and its soft glow that I have always liked. Shot in monochrome, there is an unmistakable vintage feel. Shot in color, there is a dreamlike quality.
It's the simplest of lenses: a single positive meniscus (one side convex and the other concave with an overall positive focal length to focus light).
The simple explanation regarding the optics behind the mystery is that a positive meniscus has more spherical aberration (to give you that "glow") than a biconvex lens with the same focal length and aperture. However, if the stop is correctly sized and positioned, it can have less off-axis blur than the corresponding biconvex lens. Moreover, the amount of glow can be controlled by stopping down the lens. Using a 35 mm format, the glow is quite pronounced at f/ 4 but grows much more subtle by f/ 8. This is why, many many years ago, the meniscus was called the landscape lens and also why it was used over the years in many cheap production cameras.