To understand telephoto lenses, is to appreciate its operational characteristics on both sides of the aperture ring.
As one increases the depth-of-field of a telephoto lens (stop it down toward f/16) the background becomes sharper (greater depth-of-field). The background will also appear closer (more compressed) to the subject, as compared to a wide-angle lens.
Objects in a photograph shot with a telephoto lens appear closer together, than in “real life.” The longer (more powerful) the lens, the more compressed the subject will appear. A sports photographer may use a telephoto to bring a baseball pitcher closer during his windup.
Using a medium telephoto lens for portraits will show faces in a normal perspective as compared to the distortion of a wide-angle lens. A comfortable distance for shooting head and shoulders portraits is about 5 to 7 feet from camera to subject.
When photographing wildlife, the rule of thumb is to use a minimum of 300mm to fill the frame. Getting 5 to 7 feet from wildlife is difficult. That’s why many wildlife photographers use 400mm, 500mm, 600mm or as long as 800mm lenses.
Controlling Depth of Field
One of the most creative tools a photographer has at his controlling is depth-of-field. Depth-of-field is simply the area in focus in front of and behind the point focus. Telephoto lenses have shallow depth-of-field, as compared to wide-angle lenses.
With either lens, a larger f-stop number (i.e. f/16) will produce a greater the depth-of-field. Of course, the reverse is true, a smaller f-stop number (i.e. f/4), will produce a shallow depth-of-field.
By controlling the depth-of-field one can force the viewer‘s attention to specific areas of the frame.
Think Fast when Shopping
When shopping for a telephoto lens there are many choices with the same focal length, but different apertures. Long lenses with more glass are more expenses, (i.e. f/2.8 or faster). There are two advantages to faster lenses. First, fast lenses (f/2.8), allow taking photos in less light. It’s important for wildlife photographers shooting at dawn or dusk, when the animals are out. Secondly, fast lenses produce shallow depth-of–field.
Mastering the relationship between shallow depth-of-field vs. greater depth-of-field is a basic lesson of the craft. It will open up a new world compared to the auto-everything shooting.
