Distortion and Deliberate Distortion

The optical lens we don’t even think about is the key to taking good photos, whether with professional cameras or smartphones or the Hubble telescope. The next time you curse the camera on your phone, remember these lines from Simon Winchester’s book, Exactly:

“Lens designers have discovered host of technical problems that can conspire to spoil a photographic image.”

It’s all because of those long forgotten optics diagrams from school:

Now for the English version of the best-known problems that cause distortions:

1)      Spherical aberration: Light bends when it passes from one medium (air) to another (lens material), and this bending causes distortion;

2)     Chromatic aberration: Even worse, light of different wavelengths (i.e., colors) bends by different amounts;

3)     Vignetting: Difference in brightness between points at the center of the image and those at the edges;

4)     Coma: Some points (not all) in the pic get distorted;

5)     Astigmatism: Horizontal and vertical parts of the same object get projected onto different parts of the image, thereby distorting things;

6)     Field curvature: Only some parts of a flat object are projected correctly onto the image;

7)     “Problems with bokeh”: Blurring/out-0f-focus of some parts of the image;

8)    The “circle of confusion”: The same object may/may not get projected properly depending on its distance.

The solution to all these problems has “as much to do with mathematics as it has to do with materials”, writes Winchester:

-          Maths part of the solution deals with refraction and dispersion angles;

-          Material part of the solution was the “brilliant idea of grinding two lenses of different materials such that they fitted exactly together”, compensating for the errors in the other layers.

It’s the material part that has changed over time, involving more and more, better and better alternatives resulting in “multi-element confections”:

“Optics designers are today rather like orchestral conductors, maestros who marshal and corral morsels of carefully shaped and exquisitely ground glass of varying chemistries and optical properties into configurations that will provide the most harmonic and pleasing management of light for the task the lens is designed to perform.”

And today, thanks to the smartphone and its infinite supply of apps, one then uses photo filters on top of that pic to brighten or darken it, deliberately “bokeh” it, get fish eye views and basically do every form of distortion that the lens maker worked to avoid, all for artistic reasons and to get more Like’s on social media!