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The Long and Short of Lenses
The lens is the heart of your camera. while lenses come in all sizes they form three broad categories. Namely wide angle, normal, and telephoto. For the purposes of this discussion, we will discuss lenses in terms of the 35mm camera.
The markings on the lens itself refer to distance in feet (ft), and in meters (m), distance is measured from the film plane. Also of concern is the diameter of the screw threads on the front of the lens as this determines the size of the filters that can be fitted.
Wherever possible, try to buy lenses that take the same size filters so that you do not need to buy duplicate filers of different sizes. The size of a filter is its diameter in millimeters (mm).
You may also find a red dot or line on the distance scale, this is the infrared focus
indicator and is used when photographing with infrared-red film. Of more important scale
is the depth-of-field indicators. This is an indication of the zone of
acceptable sharpness. We will discuss this later in Chapter 5.
Focal length is how long a lens is optically. The longer the focal length the closer the subject will appear when viewed through the camera.
The shorter the focal length the further away, and smaller, the subject will appear when
viewed through the camera. The focal length can be found engraved on the lens, usually
front, like so: f = 50mm.
Angle of View
This refers to the angle, measured diagonally, that the lens covers. Below are some
lenses and their angle of view. You can plainly see that the short focal length lenses,
wide angle lenses, have
a greater angle of view than the lenses with long focal length, telephoto lenses.
Wide Angle Lens
This lens has a focal length of less than 50mm on the 35mm camera. You can see a wider picture with this lens than a normal or telephoto lens will show you. Hence, the name wide angle.
These lenses are excellent for photographing a large group in a small room, landscapes, and any other application where you need a wide field of view.
The Normal Lens
This lens has a focal length of about 50mm on a 35mm camera. When you look through the camera and open your other eye, both images will appear the same size. This lens does not make the subject appear any closer or further away.
The focal length of the normal
lens is approximately the diagonal of the camera's frame. On a 35mm camera that is
about 50mm. To see this, measure the diagonal of a 35mm negative or slide. You will
find it to be about 50mm.
The Telephoto Lens
A telephoto lens will make the subject appear closer, as will a telescope. These lenses are great for shooting grisly bears, lions, or anything else that you cannot get close to. Also great for birds and other little critters who might be scared off.
The optical length of a lens is not necessarily related to its physical length. As in the case of the mirror lens. In this case you get a very optically long lens in a short package. How? The optics are actually folded inside the lens. The light enters, bounces forward, and then bounces back into the camera.
To determine just how much closer a telephoto will bring the subject divide its focal
length by 50
(on a mm camera). For example a 300mm lens will bring the subject six times closer
divided by 50 equals 6).
The Zoom Lens
A zoom lens can actually change its focal length. Looking through this type lens you can make
the subject optically appear to move closer or further away. These lenses are great to save space as one zoom lens can cover a range that
might take several fixed focal length lenses.
Go long, go short, go take pictures.
Chapter 3 Chapter 5