Basic Photography Course

Figure 1-36.Reflecting telephoto lens.

The overall physical length of a telephoto lens is

usually only about one half of its focal length. A basic,
long-focal-length lens must be placed one focal length
away from the film if it is to form an image of a subject
at infinity. In the case of a telephoto (or mirror) lens, the
lens-to-film distance is reduced considerably while still
retaining the effects of a long-focal-length lens. Thus a

1000mm telephoto lens rear element may only be

500mm away from the film when the lens is set at
infinity.

Those 35mm camera lenses that range from about

85mm to 135mm are good for shooting pictures of

people. They allow you to shoot from about 6 feet away
and still fill the frame with the subject's face. Six feet
from the subject is a good working distance. It is not too
close for comfort, and it is not so far away that intimacy
is lost.

Telephoto compression is the apparent compression

of perspective. A telephoto lens does not compress
perspective; it only appears that way! Remember,
perspective does not depend on the lens being used, but
on the position of the camera.

So then, how does a telephoto lens produce the

effect of compressed perspective? Several factors are
involved:

A telephoto lens is used from farther away to

obtain the same size image that would be produced by

a shorter lens at a closer distance. The more distant
camera position produces a flatter perspective. But,
because the long lens magnifies the subject, it still
produces a normal size image. Thus the looks are flatter
than expected.

The distance from which the print is viewed also

has an effect. An X-times enlargement should be viewed
from X-times the focal length of the lens used to make
the picture in order for the perspective to appear natural.
Therefore, a 6X enlargement of a negative shot with a
50mm lens should be viewed from 6X 50mm = 300mm
or 12 inches, while a picture made with a 500mm
telephoto lens and enlarged 12 times should be viewed

from20feet(12 x 500mm=600 x 0.04 = 240

12 = 20

feet). (Note: To convert millimeters to inches, multiply
the known millimeters by 0.04.)

A reflecting telephoto lens, the so-called mirror

lens, has folded up optics. It uses internal mirrors to
reflect the light twice. This enables the lens barrel to be

much shorter, but because of the mirrors, it must also be
much broader. As shown in figure 1-36, light that enters
the lens through a glass plate is converged and reflected
back by a concave mirror at the back of the lens. This
reflected light is directed to a small backward-facing

l-35

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> Figure 1-36.Reflecting telephoto lens. The overall physical length of a telephoto lens is usually only about one half of its focal length. A basic, long-focal-length lens must be placed one focal length away from the film if it is to form an image of a subject at infinity. In the case of a telephoto (or mirror) lens, the lens-to-film distance is reduced considerably while still retaining the effects of a long-focal-length lens. Thus a 1000mm telephoto lens rear element may only be 500mm away from the film when the lens is set at infinity. Those 35mm camera lenses that range from about 85mm to 135mm are good for shooting pictures of people. They allow you to shoot from about 6 feet away and still fill the frame with the subject's face. Six feet from the subject is a good working distance. It is not too close for comfort, and it is not so far away that intimacy is lost. Telephoto compression is the apparent compression of perspective. A telephoto lens does not compress perspective; it only appears that way! Remember, perspective does not depend on the lens being used, but on the position of the camera. So then, how does a telephoto lens produce the effect of compressed perspective? Several factors are involved: A telephoto lens is used from farther away to obtain the same size image that would be produced by a shorter lens at a closer distance. The more distant camera position produces a flatter perspective. But, because the long lens magnifies the subject, it still produces a normal size image. Thus the looks are flatter than expected. The distance from which the print is viewed also has an effect. An X-times enlargement should be viewed from X-times the focal length of the lens used to make the picture in order for the perspective to appear natural. Therefore, a 6X enlargement of a negative shot with a 50mm lens should be viewed from 6X 50mm = 300mm or 12 inches, while a picture made with a 500mm telephoto lens and enlarged 12 times should be viewed from20feet(12 x 500mm=600 x 0.04 = 240 ÷ 12 = 20 feet). (Note: To convert millimeters to inches, multiply the known millimeters by 0.04.) A reflecting telephoto lens, the so-called mirror lens, has folded up optics. It uses internal mirrors to reflect the light twice. This enables the lens barrel to be much shorter, but because of the mirrors, it must also be much broader. As shown in figure 1-36, light that enters the lens through a glass plate is converged and reflected back by a concave mirror at the back of the lens. This reflected light is directed to a small backward-facing l-35 contents Basic Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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