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If we have an image of an array of inﬁnitely small points of light which we then focus with a simple lens and we will then be able to see a variety of aberrations that the lens could produce. Light input into a lens element consisting of an array of inﬁnitely small point light sources Curvature of Field Spherical Aberration at the lens output Lens Astigmatism Comatic Flair Spherical, Chromatic Flair, Curvature of Field and Astigmatism are all types of aberrations that a simple lens will produce. So a lens designer will have to produce a lens which overcomes these problems or at least makes them unnoticeable. This property is one of the major problems a lens designer has to overcome, ‘chromatic aberration’ when different frequencies of light focus at different points. This issue is often noticeable with poor lenses when around an out of focus object you get blue or red fringing. We have all seen a rainbow and some of us may even remember the song about the colours! White light is made up of these colours and diffraction caused by the rain drops breaks the light up into its’ component wavelengths, producing the rainbow. Red being the longest, 700 nm, and blue being the shortest, 400nm. When the light from the sun enters the atmosphere this light is also refracted, the blue part of the spectrum is refracted the most whilst the red part of the spectrum is refracted the least, this is why we have blue sky and red sunsets. In the early days of CCD cameras lenses that were designed for these had a green ring around the front of the lens which was to indicate that the lens was for a CCD camera. The lens and the camera manufacturers agreed a position for the red, blue, and green sensors and positioned these sensors at an agreed distance, this was to allow for the different focal lengths for the red, green and blue light, where as in the earlier tube cameras it was possible to move the individual tubes so that the focus for individual colours would be precise. Part 2 next month... KITPLUS - THE TV-BAY MAGAZINE: ISSUE 108 DECEMBER 2015 | 45