Lighting in Photography: Studio Lighting for Portraits
After learning the basics of photography studio lighting for objects, we can apply the same rules to portrait photography. However, there is one part of the equation that changes, and that is falloff. Falloff describes how quickly the center spot of the light (or area of equal illumination) changes into the ambient illumination of the subject (light cast from the room, or other lights, etc.)
Here’s how it works: we’ll look at equal camera exposures of an identical object, but change the distance of the light from the subject.
You’ll see that the “falloff” is different in each image even though the exposure is the same. The way this was achieved is by changing the distance between the subject and the light while maintaining the strength of the light at the subject’s surface. This is somewhat difficult to do with your household lamp. Here strobes were used because in order to change the “power” of the light.
In the right image, the strobe is bare bulb and about four feet from the subject’s head at 1/8th power. In the left image, the strobe is about eight feet from the subject’s head at 1/4 power. Notice something familiar? The “halves and doubles” of your camera work the same way as “distance of the light to subject” as well. In order to prevent the change of the “power” of the light when you double the distance, you can also (roughly) double the power of the strobe.
Now look at circles B and B2. A great way to determine the distance of a strobe from the subject is to look at the specular highlight, seen here on the eye. You can plainly see that when the strobe was closer to the subject it created a larger specular highlight on the eye. When the strobe was moved away from the subject, even though the exposure did not change, nor did the values of uniform areas, the specular highlight became smaller.
Look at the background. You’ll see that the exposure on the grey background has not changed at all. Since there is only one strobe, this was not achieved by a trick of the light, only by changing the distance between the background and the subject. When the strobe’s distance from the subject was doubled, the distance between the strobe and the background must be maintained in order to maintain an equal value on both exposures (if you were to keep the power of the strobe constant, which was not). A visual perspective on all this information:
Again, you should be able to see easily that while the distance between the subject and the light source has changed, the distance between the background and the light source has not changed.
If all things remain equal (the power of the strobe) then the wall’s exposure relevant to the camera will not perceptively change but the values on the subject will.
This is an important concept because if you are using a model on location, in an alleyway perhaps, and the values of the wall behind her are too low or too high, you can move the model and the strobes together towards the wall and maintain everything about the exposure (stop, shutter) but change the relevant values of the wall.
A Key Concept to Remember: the “hardness” or edge quality of a shadow is directly relevant to the distance between two objects and the light source.
If you have a strobe four feet from a model, and four feet behind her is a wall, when you decrease the distance between the model and the light source (and move only the light, not the model) you will soften the edge on her cast shadow.
If you increase the distance between the model and the light source, you will harden the edge on her cast shadow.
The same is conversely true, increase the distance between the wall and the model, while maintaining the distance between the model and the light source and you will soften the cast shadow edges. Decrease the distance from the model to the wall (while maintaining the distance between the model and the light source) and you will harden the cast shadow edge.
Why does shadow falloff matter?
When you use multiple source lighting, it is harder to “hide” a shadow inside another if the edge quality of the shadow is hard. When the edge quality is smooth, you can light from two directions and by using a close ratio, hide one shadow within the light from the other source. This is how bilateral lighting can be achieved without having that hideously amateur “multiple shadow” result.
One more note: You MUST gray-balance your images.
For the studio photographer, or aspiring studio photographer, I HIGHLY recommend your first purchase be a Gretagmacbeth color chart. One side of this chart is 18% Gray (or, “mid-grey”) and the other side is a swatch chart with multiple colors and a gray-scale. They cost around $100 for the full paper size chart, but come in multiple sizes. If you are on set, and have a chart that you can shoot (after you have set up your lights) then you will save yourself a world of pain later in the process.
This isn’t as critical for closed system work (meaning from capture to print, you control the process) but if you plan to deliver your images to a client that will print them on their own, or deliver them to the printer, you want to make sure your images are color correct. Some of this process is done in post with the posting facility (matching color “true” items, like products, or fabrics in the image, to the “real life” counter-parts).
Color temperature is described in the Kelvin scale, and is basically (in photography) a sliding scale between “orangish” (or commonly, CTO “Color Temp Orange) and “bluish” (or CTB or “Color Temp Blue”). More about this here.
You must also consider different types of light source, like gas-electric lights (that have a flicker, and a PlusGreen / MinusGreen cast to them). One of the most common and most hideous examples of color issues is the indoor portrait with a window in frame, looking outside. When you use a digital camera with the “AWB” balance function on, you end up with hideously orange people inside, and a Smurf blue outside world in the window. It looks like garbage, so pay attention when you choose the location of your portraits. š
