Use Motion and Depth Of Field In Your Photos
While digital cameras offer the potential to bring back better pictures more easily, I find many aspiring photographers are overwhelmed and confused by the technology and abundant options for shooting. It's time to focus on the essentials, and then take advantage of the technological enhancements.
Digital cameras are still based on the use of an aperture and a shutter for both exposure and creative control, just as film was. Working with the basic principles of each still applies to every photograph you take. Exposures are all modified by adjusting the diameter of the aperture and the speed of the shutter. For determining creativity, though, the key is to remember that changing the aperture’s diameter determines the amount of depth of field, and adjusting the shutter speed determines how motion is portrayed.
Working with the automatic modes on today’s cameras helps make getting a good exposure as easy as it’s ever been. First, I’ll take a photo and visually check it for composition on the LCD. With the ‘Highlights’ feature turned on, any overexposed areas flash and show up right away. Next, check the histogram for more detailed exposure information. The extreme left of the graph is the black point, and the extreme right is white. If any portion of the graphed line touches or piles up against the white or black ends, some sections of the image are either pure white or black and have no other detail. There is no ‘perfect’ curve for the middle, the graph simply reflects varying amounts of image detail at different tonal values.
Exposure compensation allows me to easily adjust for the correct exposure. If an image is too dark, add some overexposure compensation and shoot it again. If it’s too light, use underexposure compensation to darken it. And bracket!! In any situation where exposure is questionable, or where the dynamic range of the landscape exceeds the capability of the camera to capture it, bracket by at least one full stop over and under - and up to 2 or 3 stops over and under when necessary. Although this is a very simplified synopsis of my methods for adjusting exposure, it works!
While understanding exposure and HDR (high dynamic range) compositing techniques are essential today for creating top quality digital landscape photographs (learn more about Dynamic Range here), understanding the practical applications of the aperture and shutter gives you full creative control of your camera. Pretty much any creative photographic technique works with depth of field or motion.
When setting up to take a photo, I first consider whether depth of field is more important (the amount of the image that appears in focus from foreground to background), or whether creating —or stopping—motion blur is most essential. If depth of field is more critical, as it is in most of my landscape images, I’ll set the camera to Aperture Priority Mode. I select the aperture and focus point, and the camera selects a corresponding shutter speed. If controlling motion is most important, I’ll work in Shutter Priority Mode so I choose the shutter speed, and the camera selects an appropriate aperture.
Digital cameras also have the option to change the ISO to adjust the sensitivity of the sensor to light. This allows a person to work with specific depth of field and motion requirements in varying amounts of light. While the lowest ISO settings offer the sharpest and most noise-free images, the higher ISO settings still provide better images than were available with comparable high speed film and allow us to capture images that weren’t possible with film.
Using automatic exposure modes helps cut through some of the overwhelming technology and opens up more freedom for personal creativity with less thought to mechanics. Determining creativity, though, still requires a level of understanding about how the size of the aperture affects depth of field, and how different shutter speeds can stop action, or create motion blur.
Apertrure Priority and Hyperfocal Settings
Working with Aperture Priority Mode and hyperfocal settings to maximize or limit depth of field is the best way to draw the eye from a main subject to the others in an image, or highlight specific subjects. Understanding hyperfocus settings to set the aperture and focus point so both near and far subjects are in sharp apparent focus was one of the biggest advances in my landscape photography. Most photographers understand the principle that a smaller aperture has greater depth of field than a larger aperture. Fewer photographers though, understand how to maximize the depth of field at each aperture setting by setting the hyperfocus point.
The amount of depth of field is directly related to the size of the aperture and the focal length used. The smaller the aperture and shorter the focal length, the greater the depth of field potential. When using any lens at its largest diameter aperture opening (smallest number - for example f /2.8) and focusing on a subject that is between the closest focusing point and infinity, everything in the same plane as the subject is sharply focused, while objects both closer to and further away from the camera are in progressively softer focus. Focusing on the same object while using the smallest aperture opening (largest number - f /22) increases the depth of field both in front of and behind the plane of focus.
Every lens has a specific focusing distance at each aperture setting that will maximize the amount of detail that can be in apparent focus from a near point to infinity. This hyperfocus point can be determined, with a chart, or a phone app, as well as the settings on some prime and zoom lenses. Depth of field is specific to focal length no matter what size sensor the lens is used with. The small chart I’ve created shows the depth of field for f /22 at various focal lengths. There are full charts with hyperfocus settings for different focal lengths and aperture settings in my books.
With the aperture set at f /22, and the actual focus point set to the HF (hyperfocus) distance, the apparent depth of field sharpness will extend from the NF (near focus) to infinity. When working with prime wide angle lenses I often do my focusing using the hyperfocus settings on the lens. I’ll set up the camera so it’s the right distance from the nearest subject, and then set the hyperfocus on the lens so the image is in sharp focus from the nearest subject to infinity.
For example, with a 24 mm lens at f /22, I would place the camera 1' 6" from the nearest subject, compose the shot, set the hyperfocus point to 3', and shoot without ever checking focus in the lens. Everything in the final image would appear sharp from foreground to background. If there aren’t any focus distance settings on the lens, just focus on an object at the correct distance away.
There’s also another method for setting the hyperfocus point on a lens. First, focus on the nearest object and note that point on the lens barrel. Then focus on the furthest object, and note that distance on the lens barrel. Since the hyperfocus point on the lens barrel is always half way between the near point of focus and the far point of focus, set the actual point of focus on the lens barrel midway between the near and far points you noted.
One option for checking the depth of field sharpness during composition is to use the DOF preview button. While this is most helpful for selecting a mid-range aperture with a telephoto lens to isolate subject detail, this can also be used to check depth of field for landscapes. Pressing the DOF button changes the lens aperture to the set value (rather than being wide open as it normally is when you look through the viewfinder). Since the amount of light reaching the viewfinder when using a small aperture is quite minimal, it can be difficult to see the image. Looking long enough to allow your eye to adjust to the low light can help, but in many situations it’s still tough to see fine detail through the viewfinder.
With digital cameras, the best option for checking depth of field is to take a sample photo, then zoom it to the next to highest level (just before the image pixelates slightly). Check the edge sharpness of foreground detail compared to edges of background detail. If the foreground is in soft focus and the rest is sharp, adjust the hyperfocus point slightly toward the foreground. If the background is soft, adjust the hyperfocus point toward the background. If both foreground and background detail is soft, use a smaller aperture and try again - or use a shorter focal length and recompose the image.
Shutter Speeds and Motion
The second creative camera option is using different shutter speeds to control motion blur. To best understand the concepts of using Shutter Priority Mode to control motion, it’s important to have a sense of how different shutter speeds affect the amount of motion blur with different focal length lenses.
The most basic premise is that fast shutter speeds will stop action, while slow shutter speeds allow moving objects to show some blur. In addition, the longer the focal length, the more apparent the motion. While we generally try to stop the effect of motion in an image with a fast enough shutter speed so subjects are all tack sharp, using longer exposures to create varying amounts of motion blur opens up many creative possibilities. Motion blur is created by camera motion, subject motion, or both.
The most common type of subject blur for landscapes is using a shutter speed of about 1/8 second or longer to soften the effect of the moving water. The longer the shutter speed, the softer the effect on the moving water. At about 20 to 30 seconds or so any water detail softens into a fog effect. Big waterfalls though sometimes show more of their energy when photographed with a medium shutter speed - one that is fast enough to stop action at the top, but have some slight motion blur at the bottom. A shutter speed of about 1/60 sec. does this when using a normal focal length lens.
Longer shutter speeds can be used to blur anything that’s moving - like flowers or branches blowing in the wind, moving clouds, or falling snowflakes. In bright conditions when it’s tough to get a slow enough shutter speed at the lowest ISO, 2 to 8 stop neutral density filters can be added to cut the amount of light coming through the lens and use a slow enough shutter speed to create the right amount of blur.
Using camera motion to blur subjects or backgrounds opens up a whole different range of fun and creative possibilities for working with motion blur. A camera can be panned on anything, whether it is moving, or still. To pan with the camera, use a shutter speed that is 2 to 3 stops slower than that needed to stop action. Follow the action, or lines of the subject, while taking a succession of shots through the process, so there are a range of images to choose from. Having a stabilized lens can help when tracking a moving object.
Variations on the theme include panning on still objects, like along the lines of a tree or flower stems. Or, pan on things you would normally photograph with the camera still - like falling water in a falls, or snowflakes coming down against an interesting background. Try changing the focus during the exposure, or zoom the focal length. With a rotating zoom you can adjust the focal length while holding the camera still, or rotate the camera while holding the zoom barrel still. The first method gives a zoom flare effect, while the second provides a whirlpool effect. I’ve found a shutter speed of about 1/6 sec. or so often works well for panning and zooming on still subjects.
Another option is to hold the camera still for a portion of the exposure (stabilized lens) and then pan during the rest. All it takes is having an exposure time long enough to do both processes during the single exposure time. And while this is fun to do in the camera, this doubling effect can also be accomplished by digitally combining images in an image editing program - or with multiple exposure features (Nikon, Pentax) - if your camera has that capability.
Since bright or dark areas tend to blend with opposing contrasts in the image, blurred images often have good overall dynamic range. While I occasionally work with bracketing when experimenting with motion blur, most often I find the exposure that works and has the full dynamic range, and use that for the rest of my exposures.
Experiment with these concepts and techniques wherever you are. It’s easy to set up depth of field situations and play with the camera in your home, so you are more comfortable with the techniques when out in the field. Once you comprehend the concepts of using the aperture for depth of field and the shutter to control motion, it’s all about playing, experimenting and having fun! The only constraints with a digital camera are battery life and how many images can be put on a card. With the LCD it’s easy to check and hone your composition, and then verify your exposure and image sharpness before moving on to another composition.
So, rather than working in the basic Program Mode and using your DSLR as a point and shoot, take control of your creativity with aperture priority and shutter priority. Use low ISO speeds for cleaner sharper images where there is enough light and higher ISO as needed in low light situations. Though the available depth of field and corresponding motion are somewhat dependent on the focal length lens being used, the imagination and creativity is all up to you!
The above article is adapted from Carl Heilman II's upcoming book, The Landscape Photography Field Guide, which will be available in August 2011.