Quality of Light - part 4 (effective size)

So far in this section we have seen how size affects the quality (contrast) of light. A small light source produces hard, high contrast light, and how a large light source produces soft, low contrast light. In this last discussion on the quality of light I would like to show how distance between light source and subject change the effective size of a light source.

In the diagram below, both lights are the same size, but the bottom light is positioned at about three times the distance. Again I have placed vector lines at three points along the light source to represent rays of light at the points that just touches the model's face. What becomes obvious when looking at these lines is that the angle of the lines is greatly affected by distance. When the light is close, the angle is greater than when the light is farther away. In this case the close light has about 55 degrees of spread from the light rays emanating from the extreme edges of the light source. The light that is farther away has about 12 degrees of spread from those same two edges of the light source.

As you can see, because of the smaller angle, the resultant shadow is much less feathered and is the same as would be produced by a smaller light source at a closer distance. So it can be said that moving a light source farther from the subject makes it effectively a smaller light source, at least in terms of the effect on light quality.

This concludes the discussion for the quality of light. Next post we will delve into discourse on light temperature, which will be the last section for this series.

Continue on to the next series "Temperature of Light - part 1 (Introduction)

Quality of Light - part 3 (Soft Light)

Continuing our discussion of the quality or contrast of a light source, we previously demonstrated how a small light source produces high contrast light that makes well defined, hard shadows. In this post we take a look at soft light and why this is a characteristic of a large light source (large relative to the subject).

In this next diagram I have increased the size of the light source. It is still small relative to our model, so the light is relatively hard, but it is large enough that we can start to see a slight softening of the shadow.

I have placed lines emanating from three points along the face of our light source, one at each edge and one in the center.Looking at the magnified area in the circle we can begin to see how light from the three points interact to create a feathered edge for the shadow. The background area below the red line is illuminated by light rays from all points along our light source. Light from the red point cannot reach the area of the background above the red line, so that area only contains light from the gray and blue points. Light from the gray (center) point cannot reach the background above the gray line, so that area is lit only by the blue point. Now, if you imagine countless lines representing all of the points along the face of the light source, then you can see how the shadow's feathering is the interaction of all of those lines.


In this last diagram I have increased the size of the light source to be larger than the subject. What we see is that there is now much more interaction because light from either extreme of the light source reaches all the way to the center behind our model. This results in a gradual feathering of the shadow that is considered very soft.

An extreme in terms of size, would be the sky on an overcast day, which can leave virtually no shadow.

In the next posting we will take a look at how distance between light source and subject changes the effective size of a light source.

Continue on to part 4"Quality of Light - part 4 (effective size)"

Quality of Light - part 2 (Hard Light)

Continuing our discussion of the quality or contrast for light, we have seen that a small light source produces high contrast light that makes well defined, hard shadows this type of light is often referred to as hard light. Conversely, we saw that a large light source produces low contrast light that makes soft shadows. This type of light is often referred to as soft light.

The problem with this discussion so far is that we haven't really defined what constitutes a large or small light source. We have so far also neglected the effect of distance between the light source and the subject (coming in part 3). For now I will just say that the size of the light source is always relative to the subject. Assuming the light source is relatively close to the subject, then a my idea large is when the size of the light source approaches or exceeds the size of the subject. Small would be a light source that is less than somewhere around ¼ the size of the subject.
Now that we have established some ball park metrics for size (grabbed out of thin air for the sake of discussion), let's take a look at why size matters. The following diagrams attempt to explain this, but might need a little help, so I'll do my best to describe what they are trying to show you (without getting too verbose).

For the following diagram, assume that light projects evenly from across the entire front of the light source. Also assume that the light source has a perfect reflector that focus the light perfectly at the angle shown by the yellow area (we only care about the light in the middle anyway).

In this first diagram we have a (near) single point light source. Obviously it is tiny compared to our subject. I've use colored lines (vectors) to show the rays of light emanating from this source where they just touches the sides of our model's face. Past this point behind the model, on one side of the line we have light that hits the background. On the other side the light is blocked by our model and so a shadow gets created. This shadow is clearly defined, as there is no light reflected or otherwise directed into the shadow area. What we have here is some very hard light.
In the next installment I will show how a larger light source creates a softer shadow.

Continue on to "Quality of Light - part 3 (Soft Light)

Quality of Light - part 1.

As mentioned previously, Quantity, Quality, and Temperature are the three terms used to describe light in the studio. These correlate to the more common terms, Brightness (intensity), Contrast, and Color. The term Quality is in regard to the characteristics of light. In this context we are not referring to how good or bad the light may be, as that is entirely dependent upon the desired characteristics for producing a particular lighting effect.

When describing the quality of a light source, the term Contrast is synonymous with quality. What we are describing is the relative hardness (or softness) of a light source. Hard light is high contrast, which produces clearly defined shadows that are dark and have a hard edge. Soft light is low contrast, which produces faint shadows that gently feather at the edges. The softer the light source, the more difficult it will be to see shadows.

Here is an example of hard light. This photograph was taken with a snooted monolight. The snoot is a funnel like modifier that fits over the light to reduce the effective size of the light source. In this case it is 2-¼ inches (57 mm) in diameter. The light source is about 3 ft. (0.9 m) from the subject. Note how the shadow is well defined with edges that mimic the shape of the subject.

Next we have an example of soft light. This photograph was taken with the same monolight, but fitted with a 46” umbrella. The farthest bounce surface of the umbrella is about 4-½ ft. (1.4 m) from the subject. Note how the shadow is very soft with barely discernible edges.

In part two I will show the underlying principle behind this characteristic of light using diagrams that will hopefully shed light on the subject and explain why to a photographer, size does matter.

Stay tuned...

Continue on to "Quality of Light - part 2 (Hard Light)

Quantity of Light (Intro)

As mentioned in the last post, Quantity, Quality, and Temperature are the three terms used to describe light in the studio. These correlate to the more common terms, Brightness (intensity), Contrast, and Color.

The brightness of a light source is of course measurable. The basic unit of measurement for light without deference to color is the candela, which denotes the power of light emitted in a particular direction. This is not to be confused with the older term candle power, which is based on a "standard candle" of specified composition. A candela is approximately equal to 60 candle power. The common unit of measure used in visual applications is a lumen, which takes into account the color sensitivity of a typical human eye (the eye sees green with the most sensitivity). The other unit of measure used in visual applications is called a lux, which is lumens factored over the area in which lumens are radiated. For example, a 12,000 lumen light might achieve 500 lux in your kitchen. For more info, check out the article on the Wikipedia at: http://en.wikipedia.org/wiki/Candela

The photographer's view of brightness is based on how a camera will expose and is usually expressed as an f/stop (aperture) at a given shutter speed and film/sensor ISO (100, 200, etc). A light meter is used to measure brightness and is essentially measuring lumens and displaying the measurement as an f/stop. When using a basic light meter, one sets the shutter speed and ISO, then makes the measurement and reads the f/stop.

Some meters can display measurements as an exposure value (EV). An EV is a relative measure that expresses brightness without specifying a particular shutter speed, ISO, or aperture. Like an f/stop, a change of one EV is either a doubling or halving of light intensity. The EV is referenced to zero, where 0 EV is equal to f/1 for 1-second at ISO 100. Since an EV is a relative measure, it is mostly used to express an increase or decrease in exposure. For example, if I want to open up the shadow areas (while risking blowing out highlight areas) I might increase my exposure by 2 EV.

Knowing the brightness of a light source is essential to any photographer. When using ambient light, the light meter built into most cameras is more than adequate, but in the studio, where we create our lighting more often than not with strobes, we want to set the power according to our vision, be it brightly lit, dim and dramatic, or anything in between. This is why I am an advocate of using a light meter in the studio. In a future post I would like to explain why a meter is superior to using a digital camera's histogram, but in a nutshell, it is because the histogram is based on a jpeg file generated in the camera, to which a contrast curve has been applied. It is the application of the contrast that makes the histogram inadequate. More than a few times I have bracketed in the studio because the histogram indicated that my light meter had given me an incorrect reading. To date, the light meter has always proven to be right, so I will hang my hat on my light meter and use the histogram as an approximation.

When using multiple lights, one must consider areas of overlap and calculate the brightness accordingly. For example, I set my key (main) light for f/5.6 and my fill light for f/5.6 and the fill light overlaps the key light. In this case, for a standard exposure my aperture must be set to f/8 because in the overlap area I am getting twice the light (+1EV) compared to the key light, so the proper aperture would be f/8 and the lighting ratio is 2:1.

Here is another example. If I set my key light for f/8 and my fill light for f/5.6, then for a standard exposure, my aperture must be set to f/9.5 (1/2-stop smaller than f/8). The key light has twice the brightness of the fill. Thinking in terms of units of light, I get two units of light from the key and one unit from the fill for a total of 3 units in the overlap area. The lighting ration is 3:1 and the correct exposure is f/9.5, 1/2-stop smaller than what would be needed for the f/8 key light by itself.

One last note on lighting ratios. The ratio refers to the brightest area of lighting (key) compared to the shadow lighting (fill). When someone refers to the "key light" they usually mean the physical light unit on the key side. However, when the "key light" and "fill light" overlap as they typically do, the brightness for the key lighting is the sum of both light sources, so the ratio expressed as the sum of the two lights -Vs- the fill.
Distinguishing between a key light and key lighting can be confusing because of the vagueness and similarity of those terms. Unfortunately, this is not the only place where semantics fail us in the studio. If I tell you that I used a 22" reflector am I indicating that I put a beauty dish or some such large reflector on my flash, or am I telling you that I used a 22" reflective surface to bounce light from the key light to use for fill? ...sigh.

Hopefully this illustration makes things more clear.
Continue on to "Quality of Light - part 1"

Light: In the Beginning...

I would like to spend the next few (if not several) posts discussing light. After all, photography is entirely dependent upon light in one form or another. In the studio we tend to create our own world with light to fulfill our creative vision, or at least try and get close to that vision (we do have a vision don't we?). According to Wikipedia, the word photography "...comes from the Greek φώς (phos) 'light' + γραφίς (graphis) 'stylus', 'paintbrush' or γραφή (graphê) 'representation by means of lines' or 'drawing', together meaning 'drawing with light.'"

Without getting into all the technical aspects, or if you prefer the more colloquial preface, in a nutshell, light is an energy as realized in electromagnetic radiation. In essence, light waves are the same as radio waves, but the wavelength is much shorter because the frequencies are much higher. Visible light has wavelengths ranging from 7x10-5 cm (red) to 4x10-5 cm (violet). This correlates to somewhere in the 1000 million megahertz range, just below Ultraviolet and X-Rays, and that is way up there! These waves travel away from their source at the same speed as radio waves, approximately 186,300 miles per second.

As you might have guessed, not all light is visible. What makes visible light visible is, well, us! by design our eyes can generally see light waves in the range from just above infra-red and all the way up to, but not including ultraviolet. All of these wavelengths and more are contained in sunlight. Fortunately for us, the sun's radiation that hits the earth is concentrated in the visible light wavelengths, which neatly fits our eye's adaptation. Wikipedia has some great articles on light and in particular, sunlight. http://en.wikipedia.org/wiki/Sunlight

The main point is that there are some serious physics involved and for the most part, they are well understood. The last article I read about light had dealt with slowing it down to a literal crawl, nearly stopped. There is also some discussion about light having zero mass at the wave's zero crossing points and possibly entering into another space-time continuum. I'll leave that for the physicists and simply rely on the known principles of light that I can control.

As you can see, I am trying to skirt around the physics of light and thereby not reveal my ignorance of physics. So then you ask, what is the photographer's interest in light? Glad you asked. Primarily we are concerned with three aspects of light, the quantity, the quality, and the temperature. These are common photographer terms for describing light. The more quotidian terms are, Brightness, Contrast, and Color. This is where the next few postings will delve into more detail, so stay tuned.

Continue on to "Quality of Light (Intro)"

Welcome to Studiography!

My name is Gene Lee and I am the owner and principle photographer for TTL - Through The Lens Photography (http://www.ttl-biz.com/). I will be your host on this blog and moderator for all postings.

Your active participation is welcome and encouraged. If you see an error or feel that something relevant has been omitted, please sound up! The goal here is to explore any and everything pertaining to studio photography. This includes lighting equipment, support apparatus, any kind of light modifier and different ways to use it, camera equipment, posing, advertising, networking, taxes, etc. If it pertains to studio photography, it is fair game for this blog.

In the interest of the broader community, I do read all postings and will remove or edit any that I feel violate the spirit of the blog, namely anything that I think might be offensive to other participants. The goal here is to share information and experience for the betterment of the art. Everyone is welcome here; one need only to have an interest in photography to fit in. Whether you are a beginner, advanced amateur, or seasoned pro, make yourself at home, share your knowledge, and ask any relevant question.

Thank you for stopping by.

-Gene