One of the great advantages of modern digital cameras is that you can instantly see the results of the pictures that you have taken and erase those that don’t meet with your expectations. If you’re still using a 35mm single reflex camera, or even a more sophisticated 6 x 6 camera, you don’t have that luxury.

So it is important to know what you are trying to achieve with each picture, and know how to adjust your settings appropriately, so that you get the results you want, hopefully with the first shot.

photo by D. Sinclair Terrasidius

There are certain situations that will not wait for you, such as fast-moving scenes, (a sporting event, or an airplane flying by). If you have time to make the proper adjustments ahead of time, you will have a better chance of capturing that once-in-a-lifetime moment. To do this, you have to understand the basic principles behind the optics involved in cameras and how they interact with each other.

Let’s Start from the Beginning

There exists a delicate balance between the aperture that you choose and the depth of field that you will get as a result. Let’s start out the quick review of what aperture is and how it works.

• The basics of aperture: in traditional 35mm cameras, each lens have inside of it is series of leaves that close or open, depending on the setting that the user chooses. On digital cameras, this is most often controlled electronically.
• How small or large the opening is will determine how much light comes through the lens. Obviously, the wider the opening, the more light is allowed through, and the smaller the opening, the less light is allowed to enter.
• The size of the opening is known as the F-stop, and is expressed as a number. Somewhat counter intuitively, the smaller the number, the wider the opening. For some people, this takes a little getting used to, but with time, it is an easy concept to grasp.
• The larger the F-stop (which means the smaller the opening), the more depth of field you will have.
• Depth of field is basically how much of your picture will actually be in focus. If you’re taking a picture that has both foreground and background objects that you wish to have in sharp focus, you need to use as large an F-stop opening number as you can.

Different Lenses Have Different Characteristics

It is important to recognize that different types of lenses, besides giving you a different view through your viewfinder (or screen on your digital camera) also have different optical characteristics that both affect the aperture and the depth of field.

• If you’re using a digital camera, and are trying to concentrate on a distant object, you will probably want to zoom out as much as possible. On many modern digital cameras, you can either use just the optical zoom, that is to say the amount of zoom length that the actual lens will allow, or you can opt to increase it electronically. Bear in mind that if you use the electronic zoom setting, you may experience a slight degradation in overall picture quality.
• With 35mm cameras, you have the option of either placing a zoom lens directly on the body the camera, or choosing a lens with a predefined, fixed focal length. On all cameras, including digital ones, the focal length is defined in millimetres. For most uses, a 200 mm lens (known as a telephoto lens), or similar zoom setting on a 35mm camera’s zoom lens will give decent results. For more distant objects, a lens of approximately 500 mm, which tends to be fairly big and bulky, may be required.
• Telephoto lenses by definition have a very narrow depth of field. This is just a basic intrinsic principle of the optics involved. Therefore, it is difficult to get objects in focus at various distances, even if you use a fairly large F-stop number.
• The same is true for the zoom settings on digital cameras. The optical principles are exactly the same. The frustrating thing for many people who may have been used to 35mm cameras and have transitioned to digital cameras is that the focal lengths that are expressed are not the same. But the fact remains that the longer the zoom length used, the shallower the depth of field will be.
• Wide-angle lenses, or the widest setting on your digital camera, which shows you the greatest amount of information on your screen, will have a much greater depth of field, all things being equal. Again, this is just an optical principle.
• Because modern digital cameras use digital sensors, there is no direct way to exactly convert the focal length of a lens on a 35mm camera to the equivalent on a digital camera. As a general, but only general, rule of thumb, if you divide the focal length of a 35mm lens by 1.5, you will get the approximate equivalent for a digital camera.

So How Do I Take the Picture I Want?

There are so many variables that sometimes people get confused about how they should set the camera up to get the picture they want. It must be also noted that most “point and shoot” digital cameras sometimes don’t even offer a lot of control over the picture itself. They often have some predetermined settings, such as “landscape” or “night picture”, or even “sports” which automatically adjust all the settings, but take control away from the photographer. More sophisticated digital single lens reflex cameras and traditional 35mm cameras offer far more control.

Follow these general guidelines:

• For fast-moving scenes, you will want to use a very fast shutter speed, and as a result may have to sacrifice your aperture (using a low F-stop number), and therefore your depth of field. Try to get as sharp focus on the object or person you are taking a picture as you can.
• For portraits, most people find that focusing on the subject, with a shallow depth of field (which means a small F-stop number) provides a pleasing effect, leaving the background blurry and focusing on the person.
• For landscapes, one will typically want a wide angle setting. This will automatically allow for a great depth of field. If one can, they should choose as high an F-stop number as possible to ensure that everything is in sharp focus.