Many people who use lenses have very little understanding in the complexity or the science that goes on behind them. I do not pretend to be an expert on optics but I have spent some time in trying to understand just how complex they are.
I think its first just a good idea to remind ourselves of what light is. It was Isaac Newton,1642 to 1726, who first put forward the idea that light travels in straight lines but acts as waves. Around the same time it was Christian Huygen, 1629 to 1695, who put forward the theory that light is actually made up of particles.
The first lens, as we think of them now, was first developed around the 16th Century and in terms of picture making they where first used by artists in camera obscure for drawing the layout of pictures. The famous Flemish artist Vermeer is thought to have used this to get his perspective correct.
In1835 it was Fox Talbot who used a very simple lens on the camera that he used to produce what has been considered to be the first proper photograph.
The window at Fox Talbot taken in 1835, at his house which was Lacock Abby, Wiltshire, now a National Trust property.
The early photographers used a simple lens for their pictures, not only were the pictures not very sharp but they also often had vignetting in the corners, this was because the photographic plate was not in the centre of good definition. The problem is that a lens has to be round but needs to produce an image for a square sensor, this sensor needs to be in the area of good definition.
In this illustration a single lens is focused on a sheet of paper, you can see the image fall off around the edges of the image very clearly.
A simple lens is not very good at producing a good image because it has many aberrations as well as producing distortions.