This is part 5 of the learning to light series with Josh Larkin.
In my quest to better my own lighting techniques by going back and working through lessons in various books and on websites, I've looked at apparent light size and the inverse square law. Both of these topics and exercises gave me a better handle on the three aspects of light as it relates to a subject: the lit portion, the shadow portion and the transition areas that fall in between.
However, to better understand all of this, I have to explore the lit portions of an object further, and that means looking more closely at what makes up the lit area of an object, namely, diffuse and direct reflections.
All objects produce a mix of diffuse reflection and direct reflection, and the amounts of each will change depending on the object itself. Shiny objects, black items and dark objects will often produce more direct reflection, whereas white, light colored and matte objects will often produce more diffuse reflection. Easy enough. To clarify all of this, though, it's beneficial to create some working definitions of the terms I'm using here. So let's have a look
Defining our terms
Diffuse reflections are produced by light that scatters in all directions when it hits an object. Diffuse reflections therefore do not change in brightness as the angle of view changes. We can test this by looking at a white object in a room. Walking around the room, the brightness of the object will remain fairly consistent so long as the brightness and proximity of the light source remains consistent.
Direct reflections, on the other hand, reflect off of an object at the same angle that the light hits the object and at the same brightness. So, if you hang a mirror on a wall, point a light source at it from a 45 degree angle, and then position a camera at 135 degrees, the resulting image will show a direct reflection of the light source that is the same brightness as the light source itself. Position the camera at 90 degrees to the mirror and the resulting image will be black as none of the direct reflection will enter the camera's lens.
Bearing this in mind, it's easy to understand that the types of reflections produced by an object help us to discern what the surface of the material is made of. For example, if we're photographing a glossy piece of wood, say a table top, and the position of the camera is such that no direct reflection is visible in the resulting photograph, the glossy surface will be less discernable to a viewer, as in the image below.
Now I'm going to throw out one more term -- specular highlight. As I've come to understand and use this term, it's a synonym for direct reflection. In other words, the specular highlight as it appears on an object is nothing more than the direct reflection of the light source in the object. So, if we were to take another photograph of our glossy wood surface, but this time light the table top in a way that the specular highlight -- the direct reflection of the light source -- were visible in the photograph, the viewer would then know that the surface is glossy. Notice the glare from the table below, produced by moving the light source to a position that produces a direct reflection. It's now obvious to a viewer that the table top is glossy.
But what about objects that produce little to no direct reflection, say a rectangular piece of slightly wrinkled, brown paper bag? Lighting the bag from on the camera's axis will produce an image of the paper bag with little definition, because the diffuse reflection will be similar in brightness across the entire surface area of the bag, and there will be very little, if any, direct reflection from the bag.
However, moving the light off axis will better define the surface of the bag since now we'll have areas of diffuse reflection, shadows -- where no light is hitting the object -- and transition areas between the lit and shadow areas.
So now I've got a better sense of the two main types of reflections that make up the lit portion of any given subject. And I know that diffuse reflections can be made brighter or dimmer by bringing the light in closer or moving it farther away from the subject. But what about controlling the specular highlight?
Controlling the Specular
There are two key techniques used for controlling specular highlights and getting them to work for you when making photographs, and they're closely related to each other.
First off is light size -- and if you remember back a few posts, it's apparent light size we're talking about here. Notice the specular highlight in the following picture of a CD. Pretty obvious what I was using for a light. Yep, hand held speedlight about 3 feet above the disc.
Now if I flip that flash over, and bounce it off the ceiling, that's a different story.
It's not that the specular highlight from the flash has disappeared, it's that the light source is now my kitchen ceiling, which is remarkably larger than the the fresnel lens on my speedlight. It's so large that it fills the family of angles that allow for direct reflections to be seen, and as such, the size of the highlight now covers the entire disc. So we're able to control the size of the specular highlight by increasing the apparent size of the light. And that was done by using the family of angles, the second technique used for controlling direct reflections.
The family of angles
I noted earlier in this post that a light source hitting a mirror or glossy surface reflects the light at the same angle that it hits the object. But light hitting an object typically hits an object from various angles. That being the case, it's possible to decide if specular highlights will appear in our image, and, where they'll appear, and how big they'll be. And that's control. So how do you figure out what the family of angles is? Well, here's a bird's-eye view diagram that will give you a start.
In the diagram, the angle of view of the lens is set to the outside edges of the subject being photographed. Similar to the way light reflects off of a mirrored angle, if you imagine the angle created between the camera's angle of view and the subject, and reflect it back at the same angle for both sides, the area in between creates the family of angles.
Positioning a light within the family of angles will direct light back through lens, thereby creating a photograph that includes direct reflections. Positioning a light outside of the family of angles will produce an image without direct reflections in it. And, as with the picture of CD above, if our light source is large enough to fill the family of angles, the photographed object will be entirely covered by a specular highlight.
And that brings us right back to my lede shot, an exercise taken directly from the Strobist website. The idea is to use a specular highlight to create a halo around a subject. In doing so, we're able to create some separation between the shadow side of the subject and the background.
I set this shot up during my morning coffee time and set myself up in front of a glossy wood cabinet. The light is to camera right at about 45 degrees, and slightly above eye level. I used a single SB600 fired through an umbrella using my D7000's built in commander mode. The workflow basically consisted of firing a few test shots to get the specular on the background where I wanted it, achieved by altering the light position, then putting myself in front of the camera and firing away.
And if you've been following along, you should have picked up on the fact that my skin, hat and clothes are all primarily putting off diffuse reflections. The coffee cup is glossy so it's producing specular highlights, but these have been minimized by light positioning.
I hope this provided some insight into the reflections that are actually responsible for making a photograph. In going back and working through these exercises, I've certainly gotten a better handle on another aspect of lighting control. In my next foray, I'll be looking some more at specular highlights and their importance when photographing metal. Thanks for reading and happy shooting.
Read all articles in this series:
- Learning to Light
- Get Your Flash off Camera for Better Photos
- Apparently, size does matter...
- Control Over Your Lights With Distance
- Specular Highlight Control
All of our Speedlight and Lighting articles
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