Waterfalls -- Part III

Article and Photography by Ron Bigelow

www.ronbigelow.com

Photoshop CS or Photoshop CS2 Used in this Tutorial

Shutterspeeds and Undesired Movement

The ability to use different shutterspeeds to blur waterfalls is great. It allows photographers to create different moods in waterfall images. However, a problem arises. The slow shutterspeeds that are used to produce those beautiful waterfalls with the blurred water also blur anything else in the scene that happens to be moving. Since many waterfalls are surrounded by plants, or have plants growing amongst the falling water, this creates an issue. These plants often move quite rapidly. The falling water creates turbulence in the air surrounding the waterfall. This turbulence bounces the plants around. In addition, spray from the waterfall can cause even more motion. Any shutterspeed that will blur the falling water will also blur the plants. This creates a strange looking image where the rocks and other stationary objects are sharp, but the plants are blurred. On the other hand, a shutterspeed that will stop the plant movement also freezes the water. This is particularly a problem with waterfalls that are shot fairly close up. In this type of waterfall imagery, the plants loom large, and any movement of the plants is clearly seen.

Luckily, a solution exists. Two shots can be taken, one shot uses a slow shutter speed to blur the water, and the other shot uses a short shutterspeed to freeze the movement of the plants. These two images are then combined in Photoshop through the use of a mask to produce an image with blurred water and sharp plants.

Figure 1: Image with Plant Movement Problem

Figure 1, first seen in the last article, presented just such a challenge. While the water in this image only fell a short distance, it was bounced around a lot on its way down. This created turbulence in the water and a persistent spray. This turbulence was transferred to the surrounding air. The movement of the air, along with a constant spray, caused the plants to bounce around. Furthermore, the movement of the plants was constant. Had the plant movement been caused by wind, waiting for a while might have resulted in a lull in the wind during which the image could have been shot. However, since the plant movement was caused by the waterfall itself, the plants never stopped moving. The problem was resolved by taking one shot to blur the water and another to freeze the plant movement.

Figure 2: Layers Palette

Figure 2 shows the Layers palette for this image. The Background layer contains the image with the slow shutterspeed that was used to blur the water. The Layer titled Layer 1 contains the image with the faster shutterspeed used to freeze the motion of the plants.

Figure 3 shows the mask that was used to combine the images. It might be noticed that the mask does not reveal all of the plants in the image. This is for two reasons. First, some of the plants were in the background and were not in sharp focus due to depth of field issues. These plants would not be sharp in any case, so they did not need a shorter shutterspeed. Second, some of the plants were in areas of less turbulence. Therefore, these plants were not moving so much and did not require a faster shutterspeed.

Figure 3: Mask Used to Combine the Images

Of course, when using this method, the camera must be set up on a tripod. In addition, the photographer must make sure that all camera settings, except the shutterspeed and aperture, are locked in place. In other words, the white balance, focus, and other settings can not change between the two images. This is best accomplished if the settings are set manually (i.e., the auto focus, auto exposure, auto white balance, and so on should be turned off). Needless to say, the photographer will need to compensate for the change in shutterspeed by appropriately adjusting the aperture so that the total exposure stays the same.

Even with this technique, an additional problem can remain. The shorter shutterspeeds required to freeze the plant movement will require a larger aperture. This will limit the depth of field. It may occur that some of the plants in the image with the faster shutterspeed will not be in focus because they are not within the depth of field. This requires an additional technique covered in the Waterfalls and Depth of Field section.

Aperture

With waterfall imagery, the aperture is often one of the last things to be decided. The shutterspeed is, generally, resolved first in order to determine the amount of blurring of the water. Then, the aperture is adjusted to whatever setting will produce a proper exposure for given amount of light. Thus, there is not always a lot of leeway with the aperture setting. While some other factors can be changed in order give more flexibility to the aperture setting (e.g., ISO changes and neutral density filters), even with these adjustments, the aperture setting usually has less flexibility than the shutterspeed when waterfalls are photographed. This can create problems when a wide depth of field is required.

Waterfalls and Depth of Field

As mentioned directly above, some waterfall images can present depth of field issues. For instance, it is often the case that adding some foreground to a waterfall image can dramatically increase the impact of the image. Figure 4 is a case in point. It is the beauty of the adjacent area that gives this waterfall its splendor. For my image, I considered it critical that the lush moss and grass of the foreground be included in the image. In addition, the diagonal line created by the edge of the foreground cliff added a dynamic element. Therefore, it was decided that that the foreground would be a very important part of this shot.

Figure 4: Waterfall with Depth of Field Issues

Unfortunately, the decision to include the foreground immediately caused a challenge. The foreground, with its prominent tree stump, was only a few feet from the camera. Conversely, the waterfall, and the immediately adjoining cliffs, were relatively distant. Yet, for this image, it was important that everything be in focus. It was this requirement that created the challenge. Normally, one would consider stopping down the lens to a very small aperture in order to increase the depth of field. However, this solution had a number of problems.

These problems, combined with the requirement that both the foreground and background be in focus, resulted in a decision to use that digital panacea: multiple shots. With this technique, the depth of field is dramatically increased by taking one shot with the camera focused on the foreground and another shot with the camera focused on the background (actually, many shots can be taken if necessary to get everything in focus). The images are then combined in Photoshop through the use of a mask to produce an image with everything in focus.

Figure 5: Layers Palette

Figure 5 shows the Layers palette for this image. The Background layer contains the image with the focus on the foreground. The Layer titled Layer 1 contains the image with the focus on the background.

Figure 6 shows the mask that was used to combine the images. One point to keep in mind when creating such a mask is that, when possible, it is best to have the mask cut across areas of relatively little detail. This will make it easier to combine the images so that it is not possible to tell where the images were blended.

Figure 6: Mask Used to Combine the Images

As with the previous multiple shot technique, when using this method, the camera must be set up on a tripod. In addition, the photographer must make sure that all camera settings, except the focus point, are locked in place. This is best accomplished by using manual settings.

When using this technique, there are a few of things to keep in mind. First, the tripod must be very firm so that the camera does not move while the focus is being changed. Second, the focus should be changed very gently for the same reason. Lastly, it is desirable that the images be shot in identical light. If the light changes rapidly, the images will need to be adjusted in Photoshop so that the exposure and contrast match.

One last point, this technique works better in some circumstances and with some lenses than with others. I have seen some lenses that seem to change the field of view slightly as the focus is changed. This technique will not work well with such lenses, as it will be difficult to line up the image detail in the images.

Exposure

Getting a proper exposure with waterfall images can sometimes be a challenge. Often, requirements for the blurring of the falling water and depth of field drive the shutterspeed and aperture choices that we would like to make. Unfortunately, these choices may not yield a proper exposure. In general, three types of exposure problems can occur:

Exposure: Underexposure

This is a very common challenge, particularly when shooting waterfalls with large volumes of water where faster shutterspeeds are required or in those cases where small apertures are required to produce a large depth of field. The only solution here is to increase the ISO setting in the camera (or use a faster ISO film if a film camera is being used). This will make the camera more sensitive to light. However, this does have its drawbacks. The higher the ISO, the higher the noise in the image. Fortunately, many of the newer digital cameras have very good noise characteristics even at moderately high ISOs, and the noise characteristics tend to get better with each new generation of camera.

However, even the newer cameras do have their limitations when it comes to noise. If forced to shoot at higher ISOs, the following points should help the photographer deal with the noise.

Exposure: Overexposure

This often occurs when longer a shutterspeed is desired to significantly blur the water. The first resort is to compensate for the long shutterspeed by using a small aperture. However, this has its limitations. When very small apertures are used, the image quality will degrade due to diffraction. In other cases, even a small aperture will not reduce the light enough to produce a proper exposure. This is a fairly easy problem to solve. A neutral density filter or a polarizer can be put on the lens. This will significantly reduce the amount of light that enters the camera. Most polarizers reduce the light by 1.5 -- 2.5 stops. In addition, the polarizer allows the photographer to reduce the effects of any polarized light (if the photographer does not want to reduce the effect of the polarized light, she can adjust the polarizer to the position that produces the least impact). Neutral density filters can be purchased in varying strengths and will reduce the amount of light accordingly. One option that some photographers may want to consider is the use of a variable neutral density filter. This is actually two polarizers in the same filter. It allows the photographer to adjust the filter to produce the amount of light reduction that the photographer requires. This prevents the photographer from having to purchase and carry several neutral density filters.

There are two things to keep in mind when purchasing and using either neutral density filters or polarizers. First, quality counts. Cheap neutral density filters or polarizers are likely to degrade the image quality. When I was first getting started with digital photography, I had bought a moderately priced polarizer. Many of my images kept coming out soft and had a yellowish colorcast. I eventually began to suspect the polarizer. I bought a better polarizer and the problems disappeared. Second, the more glass that is put in front of the lens, the more likely that the image quality will be affected. Thus, it is not a good idea to start stacking filters on the lens. For instance, if a lens has a protective filter and a polarizer is placed on the lens (a polarizer has two pieces of glass), there are now three pieces of glass in front of the lens. If a warming filter is added, there are now four pieces of glass -- not a good idea!

Exposure: Dynamic Range Limitations

Here, things get a little bit tricky. The falling water is white (or very close to it). The surrounding area may be dark forest or dark rock. The falling water and the surrounding area are likely to have a large difference in tonality. The reality is that the exposure has to be set to preserve the detail in the water. Unless a photographer wants totally white water with no detail, he has no choice. If the waterfall image is shot in overcast conditions (as recommended), the digital camera will, likely, be able to capture both the water and the surrounding darker areas. However, this does not get the photographer off the hook. In order to preserve the detail in the water, the surrounding area will probably get a fairly low level of light during the exposure.

It is now necessary to get into a bit of technology. When a digital camera is used, the primary issue in this situation is that the sensor is linear. What that means is that when the amount of light that reaches a sensor is doubled, the output of the sensor is doubled. That sounds innocuous enough. Actually, it causes some major issues because the opposite also applies -- when the amount of light that reaches a sensor is halved, the output of the sensor is cut in half. In other words, the darker parts of the image (i.e., the areas surrounding the waterfall) get a small signal. For those of you non-technical folk, let me translate. The darker parts of the image will not have very good detail. What it will have is a relatively high noise level (i.e., the signal-to-noise ratio will be poor). This is not a good thing. This means that the image quality in the areas surrounding the waterfall may not be as good as desired. This will be particularly true if the photographer attempts to perform image editing on these areas -- especially if the photographer lightens these areas. The detail will not be very good and the noise will become more prominent. In essence, the photographer has sacrificed the detail in the area surrounding the waterfall in order to preserve the detail in the water.

Digital to the rescue. We resort again to that digital panacea: multiple exposures. With this technique, one image is exposed to preserve detail in the water and another image is given extra exposure to increase the signal in the area surrounding the waterfall. This is extremely easy to do with the auto bracket function that many digital cameras have. The images are then combined in Photoshop through the use of a mask to produce an image with good detail in all tonal regions.

Figures 7 -- 11 show this technique in action. Figure 7 shows the first shot. This shot was exposed to preserve the water detail. While it achieved that purpose, it resulted in a very dark area around the waterfall. This is not what I saw when taking this image. I saw beautiful, lush, green foliage around the waterfall, and I desired to reproduce that in the image. In order to do so with good detail, a second shot was taken with the exposure increased. This produced the image in Figure 8. The foliage is rendered much better in this image, but some of the finer detail in the running water was lost due to clipping of the highlights. The two images were combined in Photoshop through the use of a mask. The final image is shown in Figure 9.

Figure 10 shows the Layers palette for this image. The Background layer contains the image with the exposure set for the waterfall. The Layer titled Layer 1 contains the image with the additional exposure for the foliage. Figure 11 shows the mask that was used to combine the images.
Figure 7: Exposure Set for Water
Figure 8: Exposure Set for Foliage
Figure 9: Final Image
Figure 10: Layers Palette

As with all of the multiple shot techniques, when using this method, the camera must be set up on a tripod. In addition, the photographer must make sure that all camera settings, except the exposure, are locked in place. This is best accomplished by using manual settings.

 

Figure 11: Mask Used to Combine the Images

In some cases, the two images may need to be adjusted for overall brightness in order to produce the proper results. It is often the case that the image with additional exposure may need to be darkened. This is okay. The darker areas will still have the additional detail and lower noise levels that the additional exposure rendered -- even if the image is darkened in Photoshop.

One thing that needs to be made clear is that this is not the same thing as doing two conversions in a raw converter from the same image. In that case, while the procedure may lighten the darker areas, the photographer is still dealing with an image that has poor detail in the darker areas. In other words, the photographer is using the raw converter to extract detail from the darker areas, but these areas are detail poor. With the technique in this section, the darker areas actually received more exposure; thus, these areas actually have more detail and will produce better image quality.

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Waterfalls -- Part II     Waterfalls -- Part IV