Now that we have a basic understanding of what correct exposure is (or the beginnings of one) let’s take a look at how modern automatic exposure systems do the job of setting it. My theory is that understanding the assumptions that are built into your system will help you to get the most out of it. I will also provide some tips and guidance on adjusting, and tricking, your auto and programed exposure system to achieve the kind of exposures you are after in landscape, nature, and creative work.
The Auto and Programed exposure systems in today’s digital P&S cameras are incredibly sophisticated and incredibly accurate over a wide range of lighting conditions. In my experience, they handle situations which would have baffled even an experienced photographer with a good lightmeter not so many years ago…requiring a trial and error, take a lot of shots at different settings, approach (aka bracketted exposure).
Auto and Programed exposure systems pick both the shutter speed and the aperture for any given light condition. If you are in full Auto or in Program with the ISO set to Auto, the system also picks the ISO setting.
Clearly it is the goal of the folks who program these systems at the factory to ensure that the camera captures the best possible image in the greatest number of situations. To accomplish this feat, they have to factor in the strengths and limitations of the hardware, but they also have to make some assumptions about what the average user is going to be trying to do with the camera.
And the average user, they assume, is taking pictures of friends and family…people shots…at moderate distances. Often the people are not posing…there is likely to be least some subject motion. Also, they figure the average user is not using a tripod, so there is the potential for camera motion too. They assume that up to ½ of the images will be taken at the wide end of the zoom, with people in the foreground against an open sky. They know that there will often be a significant brightness difference between the foreground subjects and the background sky.
They know the noise characteristics of their sensor at various ISOs. They know the optical characteristics of the zoom on that particular camera…where it is at its sharpest…and how zooming reduces the effective aperture and the light reaching the sensor.
It is true that, to some extent, different companies have slightly different assumptions about the exposure process, and different ways of implementing their ideas. The is also some variation in aesthetic perception among exposure programmers. There is enough consistency, however, to outline what the assumptions programmed into your Programed exposure system might be.
bias the exposure toward larger apertures (where the lenses on most P&Ss are at their sharpest, and to achieve #2)
bias the exposure toward shutter speeds above 1/125th of a second (to avoid the effects of subject and camera motion).
set the ISO to the lowest setting constant with #s 1 and 2. (on many cameras there seems to be a bias toward ISO 100, as opposed to ISO 80 or 50)
as the scene brightens, increase shutter speed before aperture
once the aperture reaches f8 increase shutter speed toward maximum before decreasing aperture any further (small zooms decrease rapidly in sharpness below f5.6)
as the scene darkens, decrease aperture first
when out of aperture, decrease shutter speed, but only to about 1/40th second.
below 1/40th second, increase ISO
when flash is called for, increase ISO to 400 (to conserve battery power and to afford higher shutter speeds to stop motion)
as the zoom level increases (moves from 1 to 3x, or 1 to 10x or whatever), bias toward higher shutter speeds, even if it means increasing ISO (to avoid the effects of camera motion, which are also magnified at higher zoom settings)
The classic P&S image. What the designers and programmers of your Auto and Program exposure systems expect to be in front of the camera.
Of course it is not as simple as that in these days of multi-pattern metering. Today’s systems actually read the brightness of several different areas of the scene and have sophisticated routines for comparing the different regions and biasing exposure based on what is likely to be in front of the camera.
For instance, a multi-pattern system might determine that the upper third of the scene is significantly brighter then the bottom two thirds. The program might be set to assume that is a classic rule of thirds landscape (or suggestion of thirds if you have read the first composition article) and try to select an exposure that will hold detail in both the sky and foreground. Or…the multi-pattern readings might be quite similar over a roughly circular center half of the field, and then dramatically different outside that circle. The program might be set to assume that it is dealing with a conventional head-shot portrait, and bias the exposure toward wide apertures, (to throw the background out of focus) while letting the brightness of the background fall wherever it will.
A rule of thirds landscape and the classic head shot.
Then there would be routines for backlit situations, and routines specifically for scenes of overall uniform brightness (outdoor, full sun light).
And all of this is on Auto or the basic Program setting. When you press the shutter release, all this measuring and computation goes on in a fraction of a second, and, nine times out of ten, produces something as close to the correct exposure as you would likely be able to achieve with a spot meter and the full zone system (you can google that, or wait for a future article.)
Chances are your P&S also has several other programs to choose from, besides the basic one. You may have specific programs for portraits, which bias the exposure more for wide apertures as above. You may have a program for action or sports which biases the exposure for higher shutter speeds and may boost the ISO setting (even beyond 400).
I bought my daughter an inexpensive (< $100) 5 Mpix Kodak P&S for a trip we are taking next month. It has programs for museums (shuts off camera sounds and flash), beach, snow, self-portrait, portrait, landscape, sports, children, backlight, sunsets, night portrait, text, and flowers…in addition to full auto and standard macro settings. Each of those programs biases the exposure subtly (or not so subtly) depending on the desired results. Children is an interesting one…it says specifically that it is for children playing outdoors in bright light, which implies to me that it is biasing toward higher shutter speeds to stop action. Sunset, on this camera, if it is well done, might also be a very useful program, since sunsets are notorioulsy difficult to expose correctly.
On the other hand, my much more sophisticated Sony DSC H9, the top of the line P&S from Sony, only has High ISO, Portrait, Advanced Sports, Twilight Portrait, and Landscape programs besides the regular Program setting and macro. But then it also has aperture prefered and shutter prefered auto, and, much more significantly, program shift (about which much more in a future article).
The Kodak has all those built in programs because it gives no control to the user over exposure…or rather, the user is given control over exposure by the wide range of programs available, and not by more conventional means like manual controls or program shift.
(It is not a bad system, and might, in fact be very good. I can see that I’m going to have to spend some time with my daughter before the trip pointing out the situations where she should get off Auto and try one of the program settings.)
For the landscape, nature, and creative photographer the built in standard program and its assumptions have implications for daily use. It should be clear that apart from specialized programs for landscape, beach, snow, etc., the programed exposure in most P&Ss is not particularly well suited to landscape, and may misread the kind of nature and creative shots we are often taking. Even the specialized programs may misinterpret what we want to capture, since what we are after is not necessarily what the average user is after.
Take a case in point. When faced with the classic rule of thirds landscape, the programed exposure still assumes that there is a subject, a person, somewhere in the foreground. Therefore it biases exposure to brighten the foreground so the face will be properly exposed. In doing so, it washes out the sky. That is the most common problem with landscapes taken on Program or Auto. The foreground is properly exposed, but the sky is bleached and uninteresting.
Many people who do landscape, creative, or nature work with a P&S adjust for this by setting Exposure Compensation (if their cameras have that feature…and many do). Exposure compensation may be on a dial somewhere easy to get to, or it may be several layers deep in the menu system. What it does is to tell the program to reduce or increase the exposure by anything from one quarter stop to two full stops…to underexpose the image by increasing the shutter speed or decreasing the aperture, or, most often by a combination of both, so that the image is darker than correct exposure, or to overexpose the image by decreasing the shutter speed and increasing the aperture so that the image is lighter than it should be.
Exposure Compensation is often called the EV setting. EV stands for Exposure Value, and it is a way of defining the brightness level for any given combination of ISO, shutter speed, and aperture…or, to put it another way…the brightness of the scene in photographic terms. Setting the EV to a minus value decreases the exposure and darkens the image. Setting the EV to a positive value increases the exposure and lightens the image. The scale, as mentioned above, most often goes from -2 to +2, with 0 being the theoretically correct exposure.
Setting the EV to, say -.7 biases the exposure to darken the sky, at the expense of darkening the foreground as well. In a landscape that can be an acceptable compromise. It can also be acceptable in macro work, where the basic program is likely to overexpose the subject, and in wildlife work, where the subject many not take up enough of the frame to expose it correctly. Only experimentation with your particular camera and its program will tell for sure.
The other classic EV compensation situation is the backlit subject. When the subject is basically a silhouette, but you want to maintain detail, you can do so by adjusting to a + EV setting. Since we are dealing, most often, with a live-view lcd which shows the change immediately, you don’t evan have to guess as to the effect. Just adjust the EV until you see the effect you are after.
A candidate for +EV compensation, or spot metering (see below)
Some nature photographers, especially those brought up on slide film, automatically set the EV to -.5 to -1, since they assume that the exposure system is balanced for flesh-tones and will overexpose more complex scenes, and since slight underexposure increased the saturation of color slides (made the colors more intense). When you are projecting an image, such added intensity is an advantage.
Underexposure has the same effect in digital systems, and a slight exposure compensation on the negative side can improve the nature and landscape performance of many digital P&Ss. it makes sense really, since most of the time we are viewing digital images on an lcd, which is more like projection, in the the light passes through the color to our eyes, than it is like prints, in which the ligth reflects off the colors on the way to our eyes.
Of course, the folks who program these systems do know all this too, so if your camera lacks EV compensation (as, for instance, my daughter’s little Kodak does), but has a unique program for macro and one for landscape (as, again, the Kodak does), chances are the programmers built the exposure compensation needed into those programs (or at least we can hope they did until proven otherwise).
Experienced photographers also use a few techniques to fool or trick the exposure program into giving them the exposure they want. For instance, almost all P&Ss will lock the exposure once the shutter release is pressed half way down. It even has a name: exposure lock. A few really sophisticated P&Ss might even have a separate button to hold exposure. Whichever method your camera uses, it is possible to trick the exposure program by pointing the camera at something darker or lighter than the overall scene and locking exposure. This is particularly effective on digital P&Ss since you can see the effect immediately on the lcd. The scene darkens and lightens as you move the camera, and you can lock exposure when it looks right to you.
This is most often used for landscapes, to quickly, without touching any camera controls, adjust the exposure balance between sky and foreground. To darken the sky, you simply tilt the camera up so there is significantly more sky in the frame than will be in your final image. Tip until the sky looks right on the lcd. Lock exposure. Then you reframe by tilting the camera back down to put the horizon where you want it. If the foreground is now too dark, then try again. When the scene is balances as you want it, or as well as you can get it, take the shot.
Conversely, if you are shooting a classic rule of thirds landscape, where the sky takes up 2/3ds of the image, you might end up with a foreground that is too dark. To reclaim some detail there, you simply tip the camera down until you see what you want to see in the on the lcd, lock exposure, reframe and shoot.
It is quick, easy, and a lot simpler than fiddling with menus or dials.
Another trick, especially useful in macro work, or where you actually do have a person in your landscape, is to put your hand into the frame so that it takes up a significant portion of the image and catches the average light in the scene. Lock exposure. Take your hand out and shoot. For macro work that insures a balanced exposure. For landscapes with figures (as they say), it insures that faces will well exposed.
Often you can adjust exposure a stop or two just by relocating a bright or particularly dark object closer to or further away from the center of the frame than it will be in the final image. Again, reframe to trick the exposure program, lock exposure, reframe for the final image and shoot. Quick. Easy. And with modern live-view lcds, you don’t even have to guess. You can see the effects of reframing, most often before taking the shot, and always after taking the shot by reviewing the image.
Finally, on may P&Ss, you do have control over what portions of the scene are measured by the exposure system.
Most P&S give you at least the choice of center or wide area exposure (sometimes called average or center weighted). Some also add spot exposure measurement (and a few of the more sophisticated even allow you to move the spot measurement around in the frame). And some have what is called multi-pattern measurement, where the camera choses which parts of the frame get the most exposure emphasis based on pre-programmed routines.
As you can see from the diagram, the areas measured by each choice are very different.
For most scenes, multi-pattern, wide area, or average exposure is adequate (especially if you use the techniques above). Multi-pattern, if available, is generally more accurate in complex scenes than wide area or average, and should be your choice.
Center or center weighted exposure would be used when you want more control over what gets the exposure emphasis in the scene. Shooting people against a particularly bright or dark background? Wildlife? Flowers? Or are you going to use the frame lock and reframe method above? Then center or center weighted may be very useful.
If your camera provides spot measurement, then you would definitely use that in strongly backlit situations to pull detail out of the silhouette. You might also use it for wildlife, birds especially, where the intense color differences between the subject and surroundings might otherwise lead to exposure errors. Of course, a movable spot can be even more useful if you have time to deal with it…however the frame, lock, and reframe method is generally faster and just a accurate.
You might use spot metering on a shot like this.
So, there you have it…understanding the choices your Auto or Programmed Exposure system is making for you, and making a few creative choices yourself, will just about ensure correctly exposed images, image after image, day after day.