Digital 101 Exposure Part 2

In conjunction with the Nikon Talk Forum at DP Review

Exposure Metering Systems-How they work...

In part one we reviewed how metering systems worked on an 18% reflectance, which takes the whole frame into consideration in making an exposure. For 80% of your pictures this works fine, but for the other 20% which has a variety of conditions this will not result in a proper exposure. In part two we will look at the different types of meter types.

The typical camera manual is designed to tell you how the camera works. They hardly ever tell you how the camera works to take a picture. Gee maybe a photographer should write the manuals. Wow what a radical concept. But it’s true so for months you wonder around with your first camera that has all the settings not knowing how to use any of them properly.

 Metering Types

The first metering type is center weighted. The center weighted metering system will have metering emphasis in the center of the frame. Since the subject is always in the center of frame if is thought that by putting the most of the emphasis on the center this will result in a good exposure. This was the main metering system for years in 35mm cameras and as you know the subject is always in the center. No way Jose.

Next there is the matrix metering. This means you can take a photo will bending over backwards dodging bullets in between jumping from building to building. Sorry I think I got confused with a movie.  With Matrix metering the frame is divided into many segments. The metering system will look at each segment and then average them all together for the final exposure. Most metering systems use some type of this system for the primary exposure settings on your camera. The amount of segments vary from camera to camera and this metering system generally gives better exposures than center weighted.

Spot metering is an over looked and seldom used metering system on most cameras. That is a shame because in most of the 20% of your pictures that have some kind of difficult lighting the spot metering is very useful. With the spot metering the camera only looks at the center of the frame and all of the exposure is based on this center 5 to 9% of the viewfinder. Let's say you are going to a concert. Most concerts are at night either indoors or outdoors. But one thing remains the same the background is generally dark and the band is in the spotlights. The exposure meter on your camera will look at the whole frame and see all this dark area and try to calculate it into the exposure.  This will result in a longer then necessary exposure in which the entertainers will be overexposed and sometimes burned up with no detail.

If you take your camera and put it in the spot metering mode then get as close to the entertainer as possible and the use your zoom to fill the frame with the subject. If you are close enough you have now eliminated the background from the photo. Now take an exposure reading with the camera in the spot mode. This exposure is based on the subject only. Take two readings, one in the brightest spot, one in the lower light spots the dark blues or reds. You might ask put why do this, since as soon as you move back these settings will change. Manual exposure is made to order. Let's say you took your readings and the bright light was f4 at 1/125th of a second and the low light was f4 at 1/60th of a second. You set either of these exposure settings in the manual mode and the camera will not change the exposure. Now it makes no difference if you are 10 feet or 50 feet from the stage your exposures will be close to the same. Distance has a filtering effect on light so you may have to add a little exposure if you are far from the stage but setting the basic exposure in manual will get you good images.

There are a few 35mm camera that have multi spot metering which allows you to take spot readings from multiple spots in the viewfinder. The camera then averages then all together to come up with the final exposure. This is a great metering system and works like a hand held light meter. But it is too expensive to be an option on only the most expensive cameras.

I’m going to stop here for tonight and the next post should be Sunday night. We will look at the various metering on your camera such as aperture priority, shutter priority, and exposure compensation and the automatic modes and how to use each.

Then we will look at difficult lighting situations such as backlighting, side lighting, dark subject light background and the reverse of light subject dark background. For homework I would recommend a search of Dirk Vermeirre posts. All photographers have their individual strengths. Some can see an image that others would pass by, some see light better than others, and some are good with exposures. Dirk takes images that are dramatic because of his use of light to make the image more powerful. He also takes images of animals at the zoo that make you forget these are zoo pictures. He captures personalities and emotion. Dirk and Jarrell Conley are the first posts I open in the forum. Find those individuals that inspire you and learn from them.

More soon.

Troutman

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