One of the ongoing challenges in photography is in converting subject matter, a third dimensional object, into a two dimension image while still maintaining a sense, or an illusion, of depth.  With practice we are able to utilize several design elements to our advantage in helping us achieve this goal. 

In outdoor photography, we’re generally dealing with two types of light: sunlight and skylight.  By positioning the sun at right angles from camera position, we add shadows to our scene.  If fill light is added to the scene, it’s weak.  In the natural scene, fill light can come from a variety of sources and it is the sun light being reflected:  clouds, water, and rock walls are but several sources of fill light.  

Another way to help create depth is by overlapping.  This is a common technique and is easily achieved.  In the example photograph above we have the foreground overlapping the sand and water which is overlapping the distant shoreline.  The rocky shoreline is then overlapping the clouds which are overlapping the blue sky.  You can effectively control depth by the amount of overlapping you place into the scene.

We don’t need sunlight to create depth in an image.  It can be achieved on cloudy or stormy days just as easily.  In the second example, the morning was spent in a light but steady rain.  Clouds and fog developed to add depth to a scene where overlapping hills were already in existence.  Atmospheric effects are a great way to create depth.

Emphasizing the use of diagonal lines is another way to create depth.  Again in the top image, there is a diagonal foreground line as well as a diagonal horizon line and at the bottom of the cloud formation is yet another diagonal line.  By emphasizing diagonal lines, we can effectively lead the viewer back into the image space. Note the feeling projected by this image, with its use of diagonal lines.  It's completely opposite the feeling of the mountains in rain and fog.  There, while still using the overlapping technique, we have lazy S-curve lines projecting a feeling of peacefulness.

Selective use of camera focus is another way to create depth.  Sometimes we can focus on a single object and create a sense of depth by throwing the background out of focus.    This is a tricky one because we can also create depth by having everything in focus, provided we’re using several of the mentioned depth cues. 

Arranging your subject matter so that it extends into the scene also helps create depth. By positioning the camera angle we can effectively create converging lines or a diminished size.  A couple of examples are railroad tracks extending to the horizon line and the long straight highway disappearing in the distance.  

In color photography, we can place contrasting colors over one another to help create a sense of depth.

We can decrease depth by placing the sun at a frontal position, or directly behind camera position.  This reduces shadows, creating a flat light with little depth.  A strong fill light will also reduce depth.

Just as we use overlapping to create depth, we can reduce depth by excluding overlapping in the chosen scene.  Additionally, emphasize the use of vertical and/or horizontal lines in place of dramatic diagonal lines. 

Different lenses can help create or diminish depth.  A long lens, or a longer focal length lens, can magnify the scene and help compress design elements.  Conversely, a wide angle lens can open up the scene, and with strong placement of foreground objects, help create depth.

By placing your subject matter on the same focal plane, equal distance from the camera, similar to the example with the leaves on log, you reduce the sense of depth.

Last, use diffused lighting, such as on an overcast day.  Remember as previoiusly mentioned regarding the mountains and fog image, you can also create depth on an overcast day.