Here is some cause and effect to consider when selecting modifer size.
Natural light comes from overhead, and key light must be at about a 45° angle to the eye line both look natural and get past the brow into the eye. At 45° above and 45° to the side of the nose the nose shadow falls over the nose at a 45° angle which covers half of it — without hanging out much or at all — depicting its 3D shape realistically by covering 1/2 the nose with the shadow.
Now consider how high the key light must be to keep it at a 45° angle in both a H&S and full length shot if a subject is 6\' tall. For a H&S shot with key light 3\' away the center of the light will need to be around 8\' hight to place it at 45° relative to the eyeline. As crop gets wider and light stand is moved back to keep it out of the shot it will be necessary to increase the height of key light to maintain the same 45° angle and lighting pattern on the face.
Now add 1/2 the diameter / length of the SB you are thinking about getting. Will your ceilings be high enough?
There\'s a concept with modifers known as \"apparent size\". A medium and large SB viewed with the larger one behind the smaller will at some point appear to be the same size. If the large one is 4x bigger it will look similar relative to the smaller one from the POV of the subject when it is about twice the distance. That\'s factors into the modifier decision because as the light is moved further back to go from H&S to full length crop it must get larger to maintain the same apparent size and characteristics.
Unless you use the modifier outdoors — where there is no reflective ceiling and walls — as you either move any light back, or substitute a larger modifier at the same distance the foot print of the source increase. Double the distance from 3\' to 6\' and the footprint of the source will increase by about a factor of 4x. If shooting in a small reflective room in your house with large modifiers you may find more \"spill fill\" light is bouncing off the ceiling and walls than is hitting directly.
Much of the \"wrapping\" quality which lightens the tone of the shadows comes from the spilled fill. A SB isn\'t needed to see this cause and effect. It\'s commonly understood that cap modifiers like StoFen and LightSphere work great indoors in a room with 8-10\' ceiling and light tone walls and why they are no more effective than the flash alone outdoors.
The degree a modifier \"wraps\" light and actually lightens shadows can be seen by taking any modifier outdoors at night and trying where there is no spill fill, then take it indoors at the same distance and compare the lighting on the face. Outdoors without \"spill fill\" it possible to observe more objectively how the size of the modifier is creating a variety of angles from center to outer edge and how well the light wraps around a high object like the nose when the light is at 45°/45° — not as much as you might assume.
As the modifier gets larger it will wrap around the round forehead and cheeks, but not the flat side of the nose. A characteristic of \"single light\" strategies is a two-tone shadow pattern on the face with the shadow on the nose winding up being the darkest, and most distracting one of the face. Outdoors where there is no spill fill bouncing back into the side of the nose even a big source will not magically make a U turn round the nose to hit the opposite side.
What photographers try to do with \"wrapping\" is make the key light also function as fill, which has the job of controlling shadow tone. I\'ve always found it better to use separate key and fill lights for the tasks of creating highlights and controlling the tone of the shadows.
If you start initially with only the fill source, centered and near chin level just under the lens of the camera it is not \"flat\" except on a flat surface like a wall. On a 3D face it will be brighter on the nearer stuff, darker on the things further away because of the inverse-square fall off. What winds up closest to the fill light when positioned that way? The nose. What will wind up having the lightest and least distracting shadow on the face? The Nose.
The fill light, falling off front > back will create a light > dark gradient from nose to ears which in a portrait will make the nose shadow noticed less because it is lighter and the ear noticed less because it will be darker. There will also be a spill fill factor from the fill source. If there is spill bouncing off ceiling and walls the fill shadow gradient from nose > ear will be different than the same source / distance outdoors on the sides of the face.
If you have never tried centered fill you will have never noticed that cause and effect, or that getting \"soft\" or \"hard\" looking lighting is mostly a matter of starting with more or less fill at whatever aperture you decide to set the lens at. Try it with direct flash. Set the lens to f/8 to keep the entire head in focus, put a flash just under the lens at chin level and then adjust power until you see detail in the black suit coat the subject is wearing. Then turn on your off axis key light and raise it\'s power until the highlights in the subject\'s white shirt are exposed just below clipping. The face in the middle of the range between the fill controlled shadows and key controlled highlights will be perfectly exposed with an \"average\" seen by eye ratio of key and fill — it will look very normal.
What you will notice by starting from a baseline of using two direct flashes is hot spots on the skin if it is damp or oily. That\'s less of a problem if the subject has a clean freshly washed face. What you\'ll observe if you repeat that test with progressively larger modifiers is that the catchlight reflections in the eyes get larger (they are the reflection of the sources) and the highlights will look less distinct, hot, and \"hard\". With key and fill at the same angles the pattern will not change.
What you will learn with this exercise is two things: modifier size has a noticeable effect on the character of the highlights and the character of the highlights affect the perception of \"hard\" and \"soft\" with lighting.
The ideal situation is to have separate key and fill sources so exposure of shadows and highlights can be precisely and separately controlled, with modifiers large enough to eliminate any \"hot spot\" specular reflections the skin. Once the modifiers are large enough to eliminate the hot spots (i.e. control over the character of the highlights) making the overall lighting seem harder or softer is mostly a matter of using more or less fill than the amount used in the test that expose the black suit correctly.
Because I worked for many years with a pair of direct flash I tend to use the smallest size modifier that is practical. For speed lights that means one that is easy to move around with. With my studio lights what is practical is limited by the 8\' height of the ceilings and I usually use a med 24 x 32 SB and 22\" dish for key and fill, respectively. I have a large SB but I rarely use it except for seated family groups sitting on cushions on the floor because I can\'t get it high enough to put a flattering pattern on a standing subjects.
On Star Trek it was said space is the final frontier. For effective lighting having enough of it is the factor which will limit gear choices and strategies for using it.
Apr 06, 2012 at 07:38 PM
Previous versions of cgardner's message #10517810 « Which size softbox? »
