Exposure Modes: Choosing The Right One To Match The Scene
Another issue pertains to depth of field. How do you control how sharp the background is when using flash? In the photo of an oncilla (#2) could I have had compete focus throughout this image? Let’s explore how Exposure modes work and how they affect these issues.
I use Program mode in conjunction with ETTL when I’m shooting fast and I just don’t have time to deal with the details and complexities of the technical aspects of using flash. For example, in photo (#3) the Makishi dancers in Zimbabwe were moving fast and Program mode was the easiest approach. I wanted to concentrate on shooting at the right moment rather than focusing on my equipment. Because the background was fairly close to the performers, the exposure is relatively uniform from front to back.
When using Program mode, this is not often the case. If background elements are far enough away from the flash such that they don’t receive enough light, they are either very dark or black. The picture of the green tree python (#4) is an example. Sometimes black backgrounds are complimentary, but much of the time it would be nice to see well exposed detail behind the subject. With animals in particular, if they are diurnal it doesn’t look right to have a black background.
In Program mode, the camera determines the lens aperture as well as the shutter speed. The shutter has to be able to sync with the flash, so it usually ends up being between 1⁄125 and 1⁄250th of a second. The aperture is determined by the ambient light, although usually the exposure system will shut down when it detects that enough light has reached the foreground—or flash illuminated subject.
Aperture Priority Mode
When the camera is set to Av (on some cameras the designation is simply “A”), the parameters are different with very different results. You now have the option of determining the amount of depth of field, and of course this gives you much more creative control. In addition, you can also get a good exposure in the background.
Instead of it being underexposed, you can have as much detail as you want. However, there is a price to be paid. In Av, the camera wants to expose correctly for both the foreground subject that receives the light from the flash plus the background that is illuminated by ambient light.
If you use a small aperture for extensive depth of field, the shutter speed becomes too slow to hand hold the camera. That means a tripod will be necessary to ensure sharp pictures.
Photo (#1) is an example. The shutter speed I used was .4 seconds because of the dim lighting in the room, and this obviously required a tripod. In addition, I had to make sure Rexie wasn’t being uncooperative and trying to escape the photo session. If he were moving, there would be a ghost image of him because the flash exposure would be sharp while the secondary image would be blurred from the ambient room light due to the long shutter.
When I photographed a model in Venice with flash and Aperture Priority in the moody light of dusk (#5) I used f/9 for extensive depth of field (the wide angle lens I used also contributed to everything being sharp), and I purposely diminished the exposure on the background.
I did this by using the Exposure Compensation feature on the camera, not the flash. The camera’s Exposure Compensation dial controls how light or dark the ambient light is. If I wanted to reduce the light from the flash on the model, I would have used the Exposure Compensation feature on the flash.
Shutter Priority Mode
I use this Exposure mode when I specifically want a particular shutter speed. There are many creative things you can do by varying the shutter. For example, you can combine a long exposure with the flash such as (#6), a picture of the Huli tribe in Papua New Guinea. My shutter speed was 1⁄2 second because I wanted to capture the blurred movement of the dancers and at the same time I wanted aspects of the picture frozen from the flash. Depth of field is not a consideration when this mode is used.
A very different photographic situation occurred when I photographed funny cars at a race track in Southern California (#7). Long exposures give you the ability to drag the shutter. This means that you can set the camera to fire the flash at the end of the exposure rather than at the beginning of it. The result is that you capture streaks of light and/or color that trail a moving subject across the frame. Usually this is done with your flash, but in the case of the funny cars, I used the light from the flashes of the photographers along the track. I used a one second exposure here (on a tripod), and I caught several flashes after the cars had left long streaks of sparks.
When I photographed Chinese dancers on stage in Beijing (#8) I used a 1⁄4 second exposure. You can see that this looks like a double exposure—one exposure comes from the slow shutter while the other exposure freezes the movement of the dancers.
I use Manual Exposure mode on the camera when I want to control both the lens aperture and the shutter speed. For example, I instruct my students during the frog and reptile workshops to use Manual mode on the camera and ETTL on the flash (iTTL for Nikon) and to set their aperture at f/32 for maximum depth of field. This means the camera is shooting on Manual but the flash is still operating on Automatic Exposure. Many of the animals we shoot are extremely small, as you can see in (#9), and therefore this required the smallest lens aperture to maintain focus. It seems to me there is no point in doing macro photography if the subjects are mostly out of focus. The intriguing aspect of getting close is to reveal all of the wonderful detail. If I used Aperture Priority, the shutter would be too slow. For wildlife, even in captivity, this doesn’t work.
By using Manual mode, I can set the shutter so none of the ambient light is recorded in the shot. At 1⁄125 or 1⁄250, the only exposure comes from the flash.
Of course, because the lens aperture is so small—f/32—that means that the flash has to be placed close to the subject. In the photo of the chameleon (#10) and the frog on the magenta flower (#11), the flash was about 5” from the animals.
Metering modes are different than Exposure modes. Metering modes (figure A) tell the meter which parts of the viewfinder it should look at in determining the exposure, and how much “weight” each area should receive. Metering modes are just as relevant in flash as they are when using natural light.
The most accurate Metering mode is Matrix in Nikon and Evaluative in Canon; it is sometimes called Intelligent or other phrases in other brands. Both systems are exceptionally good for most lighting situations. The information from many areas of the viewfinder is fed into a microprocessor which then comes back with a programmed exposure solution to the lighting pattern it detects.
Whether you are photographing stage performers as in (#12) or leopards as in (#13) this kind of metering can handle most subjects surprisingly well. I shoot with Canon, and I rarely take my camera off the Evaluative Metering mode. It can accurately interpret images as diverse as a silhouette (#14) and a typical tourist shot in a cruise ship (#15) where a person is photographed in a huge room and flash is mixed with various types of ambient lighting.
Center-weighted metering evaluates the large center area of the frame or any other area you choose and lock using the AE lock feature.
This method is accurate as long as the center of the frame is largely middle toned as in (#16). However, in (#17) where the sky is a large part of the picture—and it occupies a significant portion of the center—this Metering mode will be fooled into underexposing the picture because it wants to make the light sky middle gray. The solution in a situation like this is to place the subject in the center of the frame so the meter takes a reading on it, then you press the AE lock button, recompose the picture as you wanted in the first place and shoot. The camera will give you the exposure value that you locked into place, and then it releases that information so the following shots won’t be affected by the locked exposure.
Partial metering and spot metering are very similar. Partial metering typically reads the center 9 percent of the viewfinder, and spot metering reads the center 3-5 percent of the viewfinder, depending on the camera. Spot mode would be used when you want to read a small section of the frame such as the performer I photographed in China (#18).