My primary camera, the Canon ESO 5D Mark II has 4 metering modes:
Evaluative - Meters the entire frame
Partial Metering - Meters 8% of the viewfinder around the center
Spot Metering - Meters just 3.5% of the frame at the center
Center-Weighted Average Metering - Weighted at the center, but averaged for the entire scene
Typically I use the camera on evaluative metering, but I do check the histogram and overall balance on the display for more important shots and when I have the time. Where the scene is marginal, such as snow or sunsets I use a hand held meter, either in incident light mode, or using the spot metering. A recent example where I had to use spot metering was a sunset with buildings silhouetted in front of the sky. Spot metering the sky and the clouds enabled an average exposure that worked for the scene - provided black buildings and detail in the clouds.
Digital also brings the advantage of being able to bracket exposure without generating huge cost. Even with a 21MP sensor, I can get 300 images on a now mid-sized 8GB card. The risk is blazing away and not thinking enough about correct exposure. Furthermore RAW conversion tools such as Adobe Lightroom bring another 1-2 stops of exposure latitude. This again is risky as it can lead to laziness, however, I believe it does free the photographer to think creatively without the burden of the technology. Ironically it is the massive improvement in technology that is reducing our need to think as hard about the technical aspects of photography.
On the lighter side, the image by Alfred Stieglitz of the flat iron building in New York is very light, flat in tonality - conveying a feeling of tranquility away from the crazy bustle of the streets normally portrayed in New York. The first image in the book by Cartier-Bresson has the opposite affect to those of Weegee, the large expanse of White Wall pushes attention to the darker children in the foreground. A couple of the abstract images in chapter 10 use a bright background to drive contrast - Mohly-Nagy flattens the background in image 110 to focus on the subjects whilst Man Ray brings attention to the structure of the face by almost washing out the skin tones in image 112.
Lighter and Darker
Currently we have significant snow cover in Munich and with the Sun never getting very high in the sky, exposure compensation is more or less essential for any outdoor shots.
The first image is of recently fallen snow in a construction site nearby where I live. In order to ensure that the snow was white rather than gray I have deliberately overexposed the image by 2 stops
5D2, 24-105mm, 24mm, f/4, 1/30s, ISO 800
The following image presented a different challenge for which the solution was again an overexposure, although this time by about 1 stop. I wanted to place the building in such a way that the foreground was visible, but as the foreground is not too interesting I also wanted to include the sky. The problem is that the sky is very much brighter than the building. Because the sky was relatively featureless over-exposure would not lose very much detail, so I locked the exposure with a frame excluding the sky and then recomposed before shooting. With the sky so frequently just white cloud, little is lost by exposing for the foreground and letting the sky blow out to some extent.
5D2, 24-105mm, 24mm, f/4, 1/125s, ISO 400
The next image is the exact opposite. I was out shooting the twilight and wanted to include a building in silhouette. I framed the shot to also include the branches of the tree framing the outline of the building. An average exposure would have been dominated by the building which would have heavily over-exposed the sky. In this case I have heavily underexposed versus the camera suggestion, but then shot around 5 frames 1eV apart.
5D2, 24-105mm, 55mm, f/4, 1/180s, ISO 100
The following image was made just a few seconds earlier, but exposed for the building rather than the sky
5D2, 24-105mm, 55mm, f/4, 1/10s, ISO 100
The difference in exposure is just over 4 stops, the difference in image is dramatic. I very much prefer the first image, it has drama and mystery, the building looks on fire - I guess some fiddling about with HDR software could combine them to produce a composite, however, I suspect the combination would look very unreal and not very convincing.
My final exposure adjusted image is very different. I have been experimenting with studio lighting set ups and producing a series of different flower images. I love experimenting with light and backdrops. In particular I have been trying to create pure white backgrounds. Neither white card not felt are white enough even separately illuminated from the subject. A light tent with a Speedlite behind it and slaved is better, however, I finally figured out how to achieve this. I positioned the subject in front of a 400W studio flash with a softbox acting as the background, with a second gun positioned in front of the subject. As I was hand holding I needed a reasonably high shutter speed - 1/125s and for depth of field with a 100mm macro I chose f/16. Trial and error got me to these values. Exposure was then completely managed by adjusting the balance between the flash heads. The background was set to heavily over-expose to ensure white. The front gun used to illuminate the subject was then stepped up and down to generate different exposures. I used a flash meter to help manage the process. The first image is more or less a "correct" exposure
The second image is overexposed by a couple of stops or so, this was very subjective so I did not count too carefully
Both images have their merits, I really like them, however, the second has an ethereal quality that I am very much drawn to. So exposure is not just f-stops, shutter speed, and ISO - light can also be controlled interdependently from the camera to influence the final image - I guess this is really for the next chapter!
I have selected 5 different subjects each intended to ask different questions of the cameras metering. I have printed the 25 images in a single contact print, in each case the exposure compensation is -1, -1/2, 0, +1/2, +1 running from left to right. In all cases the images are as they came from the camera, only conversion to jpg has been done
Image 1 - Snow: This is a deliberately difficult subject for the camera as the complete frame is white with a few darker details. In this case none of the images are correct, this would require exposure compensation of a least 2 stops - the +1 image is only just starting to provide correct coloring of the snow
Image 2 - Sun: Another tough one with the Sun in the frame reflecting strongly on the icy road. Foreground detail is best preserved in the +1 image, but the most pleasing to me is the -1, as the shadow detail adds nothing to the image, whilst the bluer sky and detail in the ice speak of winter. Each image is flawed as the lens is producing flare, although I personally think this adds to the image in this case
Image 3 - Doorway: Here I have tried to produce a dark subject with a bright surround. The underexposed images lose any detail in the doorway, I prefer the +1 image as more detail can be seen in the doorway without losing any detail on the surrounding wall.
Image 4 - Moped: This is similar to Image 3, but has more content with the addition of the moped and surrounding windows. In this case the non compensated image works best, it has sufficient detail and preserves the colours better.
Image 5 - Shopping Mall: This image is completely lit by the strip lighting on the ceiling. The lights are bright and so dominate the image alongside the strong verticals of the supporting columns (which are also covered in lights). This is a complex scene to meter as there are multiple different light sources. The underexposed images lose too much detail in the upper shop so do not work. I would choose the +1/2 image in this sequence as it captures a good balance between the internal detail of the store whilst retaining sufficient contrast
In all cases following a little image manipulation in Lightroom my choice would have changed. With the 5D2 shadow detail is handled well and so pushing an underexposed image can often yield good results, however, there really is no substitute for getting it right first time around