Digital 101 Exposure Part 3

In conjunction with the Nikon Talk Forum at DP Review

Camera Exposure Control...

Exposure controls on cameras can be divided into two groups, automatic and manual. The automatic group controls every aspect of the exposure and provides limited and in most cases no ability to override. While this will do an adequate job for 80 % of images the 20 % that need the photographers touch you are just out of luck.  Why would you use this mode, basically its quick and simple. You don’t always have time to judge and adjust and this gives a very good option for these times.

Next is the manual or semi-manual modes. These include shutter priority, aperture priority, and program mode, manual mode, preset modes and exposure compensation. Once you get used to the camera you will find that these modes give you more creative control over the exposure. Most prosumer digital cameras offer a variety of ways to meter and control exposure. In this section we will look at each and how it affects exposure.

1. Shutter priority
This mode gives you control over the shutter and the camera sets the aperture. Use this mode when you want to control over action in an image.

2. Aperture priority
This mode gives you control over the aperture and the camera sets the shutter speed. Use this mode when you want to control depth of field or want both a slow shutter speed and depth of field. For instance for a shot of a waterfall where you want both a large depth of field but want to veil the water use the aperture priority mode.  View the following for an example...

http://www.pbase.com/image/2089318

3. Program mode
The program mode will take the photo automatically but does allow you to adjust the exposure. Once again this is quick and easy and if you don’t have time to adjust it can keep you from missing that important shot. Generally the camera is programmed to give you a safe shutter speed and adequate depth of field.  Here's an example of when to use the auto or program mode...

http://www.pbase.com/image/1633040

4. Manual modes
The manual modes gives you control of both aperture and shutter. I use this mode only when I want to lock in the exposure for a period of time and not have it change. This mode is very helpful for concerts where I want to hold the exposure and not have the camera change the exposure unless I want it to change.  But if you are new to photography I strongly recommend that you learn to use the manual mode, as you will learn the relationship of aperture and shutter and how to balance them.  This not a good image but what I want you to see is that the exposure is good. Used the spot metering mode, zoomed in so dark background was eliminated and then took my reading off the performer then set that reading in the manual exposure mode so the camera would not change it. All 15 exposures with this lighting are exposed exactly the same.

http://www.pbase.com/image/2382550

5. Preset Modes
Preset modes are like program modes for certain photo situations.  These modes are programmed into the camera so when you select a mode it will load preset instructions on how to deal with say for example a picture at the beach, or actions photos, or close-ups.  These modes can be very effective but it is important that you don’t totally rely on them, as they don’t cover difficult lighting situations.

6. Exposure Compensation
Exposure compensation is a very valuable tool on a digital camera.  Unlike a film camera where you most know how to use compensation A digital camera shows you how to use a digital camera.

For example…
Snow is a very difficult to properly expose because it is so white.  The metering system looks at snow and thinks the picture is too bright and then shortens the exposure and you have gray snow.  With exposure compensation you can set a plus 1.5 exposure compensation and your snow or beach pictures will be properly Yes, beach and water and sun when combined, will cause the meter to do the same thing.

The next part will be on determining exposure. About ten years ago I attended a seminar by John & Barbara Gerlach who are well know nature photographers from Michigan. John who at the time was shooting only slide film needed a way to determine exposure quickly and more importantly, accurately.  I have used his ideas and suggestions for years and they Work for both film and digital images. What I like about slide film is that it has such a small exposure latitude, of only about a ½ stop of light over or under.

You have to be right on so it is a good training tool cause if you can properly expose slide film you can expose any image properly.

But before the next post start thinking about how the exposure meter in your camera will try to average the different lighting in an image to give you an average exposure.  In other words a middle of the road type exposure.  Now as you look around you at colors start to look for the middle tone color in any image. By middle tone I mean if you have a color chart from dark brown to ivory then the middle tone would be a tan.  Not to dark and not to light like faded blue jeans, or grass, or dry wheat ready to harvest.  Everywhere you look there is a middle tone. But enough for now. Got to save something for the next post.

Click here to discuss this tutorial on the Nikon Talk Forum at DPReview...

<< [ Back ] [ Next ] >>