Zoom lenses for television
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The development of lenses of adjustable focal
lengths, the so-called zoom- or Vario-lenses, was already under way at
Schneider-Kreuznach in 1957. Two years later, production of
the first prototype began, the
Variogon
2,8/10-40 mm, for the 8mm film size. At the same time as the
development of zoom lenses for other formats, such as the Super-8-, 16
mm- and 35 mm-/medium-format, development was under way for color
television cameras with all current formats from ½"
to 1¼".
The following configurations provide a brief look
into the history of the TV-Variogons.
In studio or ENG/EFP1) configurations, they were in use
world-wide on the television cameras of leading manufacturers2).
Numerous
patents document the innovative development phase in the
seventies through the nineties.
C-Mount
zoom lenses of the 2/3"
standard construction series, on the other hand, are still today among
the range of lens products for industrial applications.
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Fig. 1:
ENG television lens
APO-Varon HM 14X,
Type TV59.02, for 1/2" |
Fig. 2
Studio television lens 30X
Variogon 2.1/16 - 480 mm,
Type TV 31, for 1¼" |
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A typical data sheet for a television lens
( pdf: 620kB )
At that time, the first 30-fold zoom TV lens with two
optical zoom groups for adjustment of the focal length , each
consisting of a zoom component and a compensator was
regarded as a technological advance. Unlike the customary
method of construction,
the patented TV-Variogon operated on the
following principle.
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 Fig. 3:
TV-Variogon with two optical zoom components
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All in all, eight operational components were
required. Three of them ( 1.2, 4 and 7 ) remain fixed, four ( 2, 3, 5
and 6 ) are axially movable to change the focal length, and 1.1 is to
adjust the camera-to-subject distance.The value s' is the distance
between the last lens surface and image plane B, the so-called back
focal distance. Fig. 4 conveys an impression of the optical components (
31 lenses in 22 elements ), which are required for this purpose.
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Fig. 4:
Optical structure of the 30-fold zoom television lens TV-Variogon 2.1 -
6.6 / 20 - 600 mm
with the shortest focal length and focus on infinity
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 Fig. 5:
TV-Variogon with two optical
zoom components
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For the mechanical realization of a larger range of
focal lengths according to the optical functional principle in Fig. 4, the
two zoom components are driven reciprocally by means of a differential
mechanism.
Patents 30x Zoom
The culmination of many years
of developmental activities in the area of television lenses was marked by
the innovative change from mechanical to electronic control of the position
of the movable optical zoom components.
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 On the occasion of the
International Symposiums 1987 in Montreux, Schneider-Kreuznach introduced
the first TV zoom lens for the 1"-picture size notcontrolled by
cam gears. The 16-bit lens controlled by a micro-processor, the TV
91, attained a 35-fold variation in focal length.
Fig. 6:
High Resolution Variogon 2/16 - 560 mm
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1) ENG - Electronic News
Gathering, EFP - Electronic Field Production
2) Ampex, Bosch, EMI, Gates,
Ikegami, IVC, Link, Marconi,
RCA, Sony, Siemens,
Thomson
Variogon zoom lens
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