Chromatic aberration

This is a lens aberration that produces colour fringing around the outlines of objects near the edges of the picture. It’s very hard to eradicate completely from lens designs without making them extremely complex or expensive, but it is possible to correct chromatic aberration using software and many cameras will now correct it automatically as they process the image.

Bokeh

This is a Japanese word to describe the particular visual quality of out of focus areas in a picture. You might think it hardly matters what things look like when they’re out of focus, but there’s a bit more to it than that. ‘Bad’ bokek produces unnatural-looking outlines and highlights, while ‘good’ bokeh looks ‘creamy’, smooth and natural. Good bokeh is associated with the shape of the diaphragm in the lens – more aperture blades and rounded aperture blades produce a more circular shape and better bokeh. Some photographers confuse bokeh with how out of focus a subject is, but that’s not the same thing. A lens with a wide maximum aperture can make background objects extremely defocused, but that doesn’t mean they have good ‘bokeh’.

Aperture blades

The adjustable hole in the lens diaphragm is created by a set of overlapping metal leaves, or ‘blades’. The greater the number of blades, the rounder the hole created and the better the lens’s ‘bokeh’ in out of focus areas. Aperture blades are often curved, too, to enhance that circular shape.

Aperture (lens)

This is the adjustable hole in the lens diaphragm that controls how much light passes through the lens and is used to adjust the exposure. Aperture setting values are the same across all cameras and lenses, and here’s a part of the series: f/2.8, f/4, f/5.6, f/8, f/11 – though the theoretical aperture range is much wider than any single lens can manage. The maximum aperture – how wide the lens opening can go – is a big selling point because wider apertures let more light through. The lens aperture also has an effect of depth of field, or the near-to-far sharpness in the picture, and the number of aperture blades is a selling point because it affects the way the lens’s ‘bokeh’.

Aberrations

These are optical flaws produced by camera lenses and which are largely unavoidable except in the most expensive or the simplest lens designs. They include distortion, chromatic aberration (colour fringing), vignetting (corner shading) and edge softness.