Welcome to the Essential Light Photography Blog By Jim Sabiston

Sunday, September 19, 2010

Hey! Meter THIS, buddy!

Last post we took a look at exposure compensation on the family point-n-shoot camera. Today we will look at a different way to control the camera's automatic exposure mechanism that doesn't require fussing with all the controls.

Whenever you point your automatic camera at a subject, the camera's light meter adjusts the aperture and shutter speed to what it 'thinks' is the best combination of settings to give the best photograph. Modern cameras have gotten very good at this. As long as there is sufficient light and the level does not exceed the dynamic range of the sensor, it is quite easy to end up with very respectable images from a technical point of view - sharp focus with a decently balanced exposure. As we covered last time, adjusting the exposure compensation moves the 'center point' that the camera uses for averaging the exposure either up or down as desired. This works quite well, but once set you have to live with those settings unless you go back to the menu and change the setting yourself. No big deal really, but it is just one more thing to forget when you are supposed to be having fun.

There is another easier, faster way to achieve the same result, and it does not require accessing any menus that you have to remember to go back and reset. All you have to do is point the camera at a spot that is lighter or darker than your subject, push the shutter button half way down to set the exposure and focus, swing the camera back to the actual subject you are interested in and push the shutter all the way down to complete the shot. It's that easy and fast.

One of the great advantages of the modern family camera is that the image on the sensor is shown on the rear lcd screen. It is this feature that makes our little trick workable. Lets try a little exercise:

Take your camera somewhere where there is a significant variation in light range. This can be inside near a lamp or outside in an area with mixed sun and shade. Turn on the camera and slowly sweep it across the scene such that you cross both dark and light areas during the sweep. Watch the lcd to see what happens to the different light and dark areas as you sweep across the scene. What you are seeing is the camera constantly adjusting to the light conditions as you move it. These changes are reflected right on the lcd! You can actually see the averaging being done in real-time.

Now, do the same sweep again, but this time at some point pick a fixed target, say the brightest spot in view, and push the shutter button down half way. You will see (and probably hear) the camera set the exposure and focus for that particular scene. This happens very quickly, usually in about one second. Once locked, continue the sweep while continueing to hold the shutter button in place at the half depressed point. Notice that the camera is no longer adjusting for the changing light conditions! Once the shutter button is partially depressed, the camera locks its settings until either the button is released or you push it down all the way and activate the shutter, taking a photograph. You can use this characteristic to your advantage.

The idea here is to simply use the natural automatic meter function of the camera to do the hard work for you, but to still have the camera take a picture that is quite different from what the automatic settings would give. I have included two images below for examples. Both images are of the same stairway outside the Morgan Library in Manhattan. I selected this spot as it had some interesting detail and textures and, most of all, some great reflected dawn sunlight shining right on it. The photographs are taken within seconds of each other, so the conditions are identical in both frames. Notice the dramatic change in the images, however!

The first shot is taken 'straight'. I placed the camera between two upright columns, framed the details I wanted and then activated the shutter. The camera did all the work. The reflected lighting is fairly soft, so the entire scene is within range and we end up with a good detailed image. While the camera did a great job of recording the actual scene, the image is otherwise rather uninspiring  and the brightest areas are actually a bit 'hot'.

(click on image to enlarge)

Next, I took the camera and pointed it at the bright blue sky and pressed the shutter down halfway. Once the camera audibly registered the exposure, I turned back to the stairs and tried to repeat the composition from the first shot - all the while holding the shutter button in the halfway position. Remember, this prevents the camera from readjusting the exposure to the darker stair scene. Once in position, I activated the shutter. Notice the dramatic difference between the two images.

(click on image to enlarge)

This image is probably a little too dark, depending on exactly what I was going for, but notice how much more dramatic the light is!  This shot illustrates one of the two main drawbacks of this method of adjusting the camera metering: the inherent lack of precision. The good news is, assuming you have the time to try different settings, is that you can see the effect right on the lcd and quickly meter to a different lighter or darker target as needed. With practice, you can get fast, consistent results. The second drawback is the potential impact on sharp focus. The camera sets the focus on your target at the same time it sets the exposure. If the difference is extreme enough, your shot can be noticeably out of focus. The trick is to try to find a metering target that is roughly the same distance as your final target. This is potentially more of an issue with closeup shots. The small lenses in these cameras are actually pretty forgiving on this point, but it pays to be aware of the issue so you are less likely to be surprised by it.

So there you go! Quick and easy 'manual' exposure control of your automatic camera.

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