2D Light Depth Calculator

Last time I talked about light depth and calculating it in one dimension, now I will add another dimension. The 2d depth calculator I have created lets you handle more complex scenarios and is more visual. The drawing is to scale, but the scale is whatever you want it to be. If you want to use centimeters, then each square represents a centimeter. If you want feet, then each square is a foot (a square foot more accurately). Each solid cintrifical line represents a full stop of light difference from the previous solid line. Dashed lines, available at greater distances represent 1/3 stops. The amount of light loss you are willing to accept from the front of the subject to the back of the subject is up to you.

To use the tool:
Determine an appropriate scale for your subject. ie. Shooting a car or group of people you may want to use feet. Shooting a lego design, you may want to use a lego standard, 1 stud. etc.
Measure your subject in the scale you have chosen. (A lego figure is about 1 stud deep, and 2.5 studs wide)
Using another piece of paper with the same grid on it, cut out your subject based on your measurements.
Place the cutout on top of the lighting calculator and move your subject around to find the perfect distance for your effect.

So if you move your subject real close to the light source, you will notice the front of the subject will be 1 stop brighter than the back. Move your subject back and now your subject bay only have 1/3 stop difference from front to back. But this is a 2D calculator, so you also see where the edges and corners start to drop in light.

Attached is a low res version. It will still work fine. So go ahead and print it full page.

Professional Photogaphy Lighting Depth

I have recently been thinking of lighting depth for use in photographing anything from a group of 40 to a shot of a toddler. When shooting an older child, adult, or small group you can get away with just placing the light and exposing. However when shooting a toddler, the risk is the little one will move closer and farther from the light as they squirm and do anything they can to not cooperate. When shooting a large group the issue becomes getting the people in the front and the back exposed the same.

Lighting depth works just like lens apertures, using the inverse square law. Because we are already used to aperture numbers (2,2.8,4,5.6,8,11,16), we can apply the same numbers to our distance calculation. For example. If our light is 4 feet away from the subject and our background is 8 feet away from the light, the background will be 2 stops darker. This is the same as the brightness difference between f4 and f8. If the background was 5.6 feet away it would only be 1 stop darker. Knowing this you realize you can do a bit of calculation in your head.

Something else to consider. Just to point out the relationship here, you can make your background darker by moving the light closer to the subject or by moving your subject closer to the light. If you move the light closer to the subject, it will also get closer to the background, but the background will actually get darker when you've properly exposed the subject.

This can be a bit to think about, so I will leave this here and follow up with my 2D Lighting depth calculator next time. I am going to try to make this available as a download for you to use.