A photographer and appearances

Our photographer draws our attention to how differently the same objects appear in different light.  It’s a lesson easily generalized.

Like many towns and cities in the US, much of Alexandria has straight streets laid out in a grid system; and like many similar places, the streets are generally north-south and east-west.  For much of the year, the east-west streets receive sunlight at a shallow angle in the morning and evening (our astronomer will explain why if you wish).  What looks like an uninteresting whitewashed brick wall during the height of the day acquires a prominent texture, and small angles throw shadows into high relief.

This is only part of the effect that the angle and quality of light has on objects.  It is our photographer’s business to notice these things, because (as a prominent teacher of photography says) light is all he really has to work with.  But most people are less aware of the angle of the light.  Someone who lives in the house in the picture might be less interested in the texture of the brickwork than the fact that he’s finally home after a long day.

Astronomers of the eighteenth and nineteenth centuries, in many cases, were also not aware enough of how appearances change with subtle differences in illumination.  This is less forgivable; scientists are supposed to be more careful about their data.  But even the great Sir John Herschel stated that the crater Linneaus on the Moon had disappeared, when it had only become less prominent under a different angle of sunlight.  Several lists of stars of the mid-1800s flag many as possibly changing in color or brightness, when we know now that they’re doing no such thing.  Once photography and then electronic instruments appeared, these more objective methods showed that the human eye-brain system was rather more variable than had been assumed.

But even chemical and electronic recording are not infallible.  If a bright object has a sharp edge, for instance the inside of Saturn’s rings, an image will show the very edge as brighter than the rest.  In the eye, this is an optical illusion; in a photograph, it comes from chemical reactions in adjacent areas; in a CCD, the explanation is electronic.  And that’s before any software is brought into play.

The lesson is to know your process.  How is it, exactly, that you caught the image, gathered the data, processed everything, and inferred the result?  Scientists think this through explicitly, and even then get caught sometimes.  Photographers, working in a different direction, sometimes do not get the results they seek.

Most people are not photographers or scientists.  But everyone gathers data to make inferences; and there are many things like the angle of the light to take into account when deciding what has actually happened.