That Word Specular

by ralph

As in the phrases “specular light or specular reflection”. It seems that recently many photographers have been using the word specular and, like the queen in “Alice in Wonderland” when they use it, it means just what they want it to. It seems as if the poorly understood term hangs in the back of many photographer’s mind’s and is pressed into service when some unusual lighting situation needs a “handle.” If specular ever had a clear meaning, it is getting lost in a fog of contradictory usage. Even dictionaries are vague because they embrace both ancient and modern definitions and none that are relevant to photography. This word is a good example of a term that has gradually evolved to the opposite of its original meaning. One dictionary entry is: “produced by a speculum,” referring to the old roman word for a (necessarily, at the time) metallic mirror. In fact speculum is still used for special medical and dental mirrors.

Another definition, “mirrorlike surface of a lake” gets more interesting. That mythological Greek, Narcissus, was definitely on to something when he got carried away with his reflection in the water. Here was a clear reflection from a mirrorlike but non metallic surface. This kind of reflection is particularly significant in photography because it is partly to wholly polarized, depending on its angle to the surface. Since polarization is something we can control, we want a word that leads us to this very special kind of light. So the term specular is used to describe just the reflection from a glossy or mirrorlike but non metallic surface, particularly to the exclusion of its opposite – a reflection from a metal.

Now we photographers certainly depend on reflections – light reflected off various surfaces or particles is really 100% of what we shoot. There are three kinds of reflection that fill our lenses. The commonest kind is just plain diffuse reflection where light striking the subject (like bricks, trees and people) is totally scattered, willy-nilly in all directions. Your lens has the job of reassembling a small bundle of this light into an image. A second kind is a metallic reflection. When the metal surface is perfectly smooth the light is bounced back, intact and without scattering, retaining unchanged optical characteristics – in other words an unscattered image. This reflection is put to heavy use getting the picture of the bride putting on her veil. (Oh right – you say the mirror is made of glass. Well that’s irrelevant because 95% of the light reflects off the silver that is plated on the mirror’s back surface). Imagine that you painted a wall with bright red, flat wall paint. The light reflected would be diffuse and would show the rich color but if you used gloss type paint the glare off the shiny “skin” could actually obscure and wash out some of that color. It’s harder to see the nice rich color of a car on the hood or roof where the gloss picks up the sky, than along the side where the darker ground affects it less. So out comes the polarizing filter to wipe away some of the shiny surface so we can better perceive what’s underneath.

The commonest use of the filter is to darken the sky. Ultra fine particles also polarize light even as they scatter it. That’s why the light from the sky is polarized and can be controlled with a polarizing filter. At just the right angle (about 90 degrees to the light source) the haze cutting and sky darkening effect is most noticeable. Unfortunately when you remove the polarized light from the sky you can also strip the blue (sky) reflection off water so I tend to use the filter much less when a lake or river is in the foreground. Garden and landscape photographers appreciate the way the polarizer removes the shine from glossy foliage revealing richer color underneath. The angles of the leaves to the sun are obviously quite random, but enough are affected to show real improvement. Another application is shooting through glass, like show
indows. At the appropriate angle (ranging from 35 to 45 degrees) unwanted reflections are totally wiped out and at other angles they are proportionately reduced. All these tactics are ways of controlling specular reflections.

It struck me as unhelpful in the extreme when I saw an article about photographing metal objects babbling on about “specular reflections”. Just because the word is back in style doesn’t justify going back a couple thousands years for a definition.

Another recent use also seems uncalled for. It is a common studio practice to light shiny metal objects with very broad light boxes or broad reflectors. The shiny metal would stay black if only direct light was used. The broad highlight however, can look rather flat, almost grayish, so the latest wrinkle in savvy lighting is for the light box to have a “hotter” or brighter center. That gives the highlights more roundness. They (often advertisers) call such lighting “more specular”. Sorry, I really don’t see how such a use fits – they just grabbed the nearest handy word for a new lighting style. Then there’s the attempt to describe those sparkly points of light that liven some subjects and provide the “stars” when starburst filters are used – as “specular light sources”. Well I’ll go as far as specks.

- - - - - - - - - - -

----and here’s a related topic;

The process in which a word evolves to take on the opposite of its original meaning can be slow and subtle or occasionally quite sudden. Digital photography has felt quite free to carve out some new meanings for well known words but if you haven’t heard this one yet you’ll be amazed. We’re all familiar with “Depth of Field” and the tireless efforts we expend to stretch it out to sharpen the whole subject – or occasionally to decrease it substantially to minimize distraction. It seems that many digital cameras (especially the cheaper ones), have tiny image chips and tiny focal length lenses to cover them. Many “normal” lenses are in the 7mm to 9mm focal length range and in consequence have tremendous depth of field. As a result everything is uncontrollably sharp. Believe it or not, some digital photographers even get envious of the soft backgrounds us film guys come up with, (yes it’s true, the grass is greener in -------------),

Now keep in mind that a digital image is never very far from an image editing program sooooo would you believe that several articles have been written in digital photo magazines showing how to blur out backgrounds? OK, now would you believe that they’re always titled something like adding, enhancing or increasing depth of field.

I kid you not!