Part 5 - Putting It All Together - Step by Step

Let’s end this exposure discussion by walking through the process I used for taking the landscape picture shown below. I'll base my exposure on histogram results and the second question photographers must address to determine the correct exposure (depth of field and subject motion considerations).

This picture taken at Zion National Park utilizes depth of field that is measured in miles -- from the blades of grass in the foreground to the farthest mountain top. In terms of densities, the full range of deep blacks to the whitest parts of the clouds require a careful exposure to ensure that both extremes retain the detail of the original scene.

Here's my typical sequence of photographic considerations and decisions:

1. The camera is mounted on a tripod. (See my footnote at the end of this walk through.)
   
2. I composed the image through my viewfinder. That was easy enough to say. Composition is a learned skill that will be the topic of later posts.
   
3. In the case of this image, stopping action is not a major concern. Mountains move very slowly. However, depth of field is of critical importantance. I wanted all the objects, from those closest to those farthest away, to be in focus. This requires an extreme amount of “depth of field” – a very small aperture opening. Remember to think backwards at this point. Great depth of field distances are achieved by using f/stops with high numbers (i.e. 8, 11, 16 and 22). The larger the number, the smaller the physical aperture opening.
4. Realizing the importance of the aperture setting to this scene, I selected the “aperture priority” mode and dialed in an f/stop of 16. (Refer to your camera's manual and learn to love "aperture" and "shutter" priority modes.) Now the camera will make exposure adjustments using only the camera’s shutter speed controls. (If the camera determines more light is needed, a slower shutter speed will automatically be selected. If the camera decides it needs less light, a faster shutter speed will be automatically used. The f/stop selection I make will NOT be touched.)
5. I decided to use the histogram display on my camera instead of a gray card. Knowing that I’m taking a general landscape scene, my meter should provide an exposure that’s close.
6. I took a test shot using the auto mode function and immediately evaluated the histogram display shown below:
   
   
   
   
   The histogram from the first test exposure indicates that the exposure settings will produce an image that’s too dark and lacking significant detail in the darker parts of the picture. A new exposure that allows more light to enter the camera must be determined. Increasing the exposure will move all the densities toward the right.
   
   
7. The exposure is close, but too much of the density range is pushed together at the dark (left) end of the graph. This will probably result in dark areas of the picture that lack any detail.
8. I adjusted the exposure compensation control on my camera to allow more light to enter the camera and move the histogram toward the right. Remember, because I fixed the f/stop by using the “aperture priority mode”, the camera adjusted only the shutter speed control to increase the light entering the camera.
9. Another picture is taken and a new histogram is presented on the LCD display. (see below) The densities have moved position on the graph, away from the left border. I know that my highlights and shadows will contain all the detail I want in my final print. Don’t be lulled into thinking that your image editing software will save a bad exposure. Light and dark areas that are totally devoid of detail data in the digital file cannot be fixed. There is no information in the file to fix! Correct exposure is everything. Get the detail in the original exposure.
   
   
   
   The second exposure resulted in this histogram. Notice that all of the densities have moved to the right to cause a separation in the darker densities. This density shift was accomplished by using the camera’s exposure compensation control to temporarily override the auto exposure and increase the amount of light that enters the camera. The print from this digital file will contain a full range of densities and detail.
   
   
10. The image preview on my camera’s LCD display confirmed that my composition was just what I was expecting.
11. Done. Well, not quite. Just to make sure that I didn’t accidentally shake the camera or that mountain didn’t unexpectedly move during my exposure, I took one more picture as a precaution. This practice has saved me on more than one occasion and is especially true when taking people pictures. Everyone tries not to blink. But someone always does. Take extra pictures - including pictures taken with the surrounding shutter speeds if you have any doubt. Better safe than sorry. You can always throw them in the virtual trash.
12. Make notes on the conditions, date, time, location, etc. for future reference. Your digital camera will automatically log the technical details of the picture with your picture file. (Metadata - a subject for a later post.)
13. When you return home, download and review ALL your files. Make special note of everything that worked and determine what might have caused disappointing images. Each successive photographic shooting session will result in fewer poor images. You may well decide you don’t like an image after you see it on the large monitor, but these will be rejected for artistic reasons – not as a result of incorrect exposure.

A note about tripods: Tripods make interesting fuel for camera club and Internet blog debates. When I hear these discussions, I’m reminded of a study I read over 20 years ago in the heyday of conventional film and 35mm cameras. The study was conducted by one of the popular camera magazines. The objective was to determine if there was a visual difference in the sharpness between pictures taken with and without a tripod. The researchers took hundreds of pictures at virtually all shutter speeds with and without a tripod. The initial results were logical and expected. At slow shutter speeds, the pictures taken with cameras mounted on tripods were noticeably sharper.

What was surprising was that when all of the pictures were magnified and examined, the same was true at all shutter speeds. Even at 1,000th of a second, the pictures taken with a tripod-mounted camera were sharper than the images taken with a hand-held camera. Since then, my camera can always be found on top of my tripod. (I occasionally use my tripod's smaller brother - a monopod. Some camera stability is better than hand holding.) If you're just beginning, I suggest that a tripod be your second purchase. As Adrian Monk would say: "You'll thank me later."

A note about depth of field previewing on DSLR cameras: Modern cameras show you the image in the viewfinder with the aperture open to its maximum setting. This is done to make the image as bright as possible for composing the scene. Check your camera's manual. You should find that your camera is equipped with a "depth of field preview button". The depth of field preview button mechanically closes the camera’s iris to the f/stop you have selected as long as your finger remains on the button. This is a great feature but takes some getting used to. By actually seeing the depth of field through your lens, you’ll know exactly which f/stop to use for your situation. However, when the camera’s iris is stopped down to its smaller openings, the viewfinder becomes very dim and it can become difficult to see which objects are in and out of focus. Learn to "look through the darkness" and see which portions of your image will be in focus. If you need more depth of field, select a smaller aperture opening (a larger f/stop number).

This is certainly not everything there is to learn about taking pictures. But by following these basic techniques, you will return home with pictures that are well exposed and very printable.

As always, if you have questions or comments, you know where to find me.