What creates soft shadows in photography?

Answer 1

Sharp shadows are indicators of 'sharp', high-contrast producing lighting.

A relatively small light source will produce a sharp shadow regardless of intensity.

The son and the moon are large, but are relatively small sources of light.

On a bright, clear day you can hold your hand out and cast a shadow of your hand on the ground that is sharp enough to see the fingers.

On a bright, clear night you can hold your hand out and cast a shadow of your hand on the ground that is sharp enough to see the fingers against a light surface.

Inside, the exact same idea applies. The flash on a camera is a tiny, almost point light source. It always creates sharp shadows. The angle from lens to subject and back to flash is usually very small. A light source never 'sees' the shadows it creates, regardless of how sharp they are.

On a clear day or night as the sun or moon is setting, you can minimize the shadows by making sure the light source is behind you as well as you can and that the subject is not too near another object to reveal its shadow. If you were on the moon, the sun would still appear as a small light source. When the relatively small object of the Earth got between you and the tiny light source, it would very quickly become very dark. If you are on Earth for the same occurrence you see the sharp shadow of the planet you are on eclipsing the moon.

Answer 2

Short Answer: Use diffuse lighting - the larger the diffused light source, the softer the light and the softer the edges of the shadows. A cloudy sky (not direct sunlight) is a good example of very soft light.

Why a Cloudy Sky?

Actually, a cloudy sky will diffuse the light of the sun. Sunlight passes through clouds and is diffused, or, no longer focused. Any material that breaks up a strongly focused light source (like the sun) will diffuse the light. You could use a bedsheet to diffuse the light, but it would probably also make the light darker.

Photographers use large boxes called soft boxes to diffuse highly focused strobe lights. These are often large black boxes made of material in which one side is a thin, translucent white material that diffuses the light, so that it creates soft shadow with no hard edge. The bigger the soft box, the softer the shadow.

Clouds are the biggest light box you will ever find and they create the softest shadows.

Why not the Sun?

The sun is the most powerful light source you can use. From the distance that we see it, the sun is effectively a point source of light. That means all of the light we get from the sun is efectively coming from the same direction. This creates very crisp shadows with very hard edges.

What about Strobe Lights?

Strobe lights are also effective point sources of light. They create very harsh shadows unless you use something to soften the light. This can be a screen, a thin sheet of translucent material (plastic or cloth) or some other similar material. Professional photographers often use soft boxes to diffuse the light from a strobe light.

This is also why on-camera flash pictures usually look horrible.