Colour Fringing

When a ray of light is shone through glass, the light is bent at a different angle because the glass is denser than air, thus slowing down the speed at which the light is travelling through the glass.  This process is called “retraction”.   Light is made up of different coloured light, all of which are on different wavelengths and bend at different angles.  It is the job of the lens to bend these rays of light back to one point to create a sharp image, however sometimes not all the rays are focused completely at the same point as the others.  This can cause what is called “chromatic aberrations” in your image, which are certain colours “leaking” into other parts of the image.  Lens manufactures have developed ways of fixing these aberrations by using aspherical elements to bend stray light to the singular point. You should look at buying these types of lenses as they are sharper than most other lenses.