Reference Guide

An Explanation of Aspherical
Elements.
Aspherical elements exhibit several
characteristics which are extremely
difficult to achieve using
conventional spherical designs.
Most importantly, they eliminate
image-degrading spherical
aberration, which results in
reduced sharpness and low contrast
in other formulas. They also
minimize pincushion and barrel
distortion while reducing flare.
Moreover, they reduce size and
weight while improving optical
performance. They are most
effective in moderate focal length,
wide aperture, and zoom formulas.
With so many inherent advantages,
it's easy to see why Canon places
such emphasis on the use of
aspherical lenses whenever
possible.
Canon's experience in aspherical
lenses dates back to 1971, when we
introduced the FD 55mm f/1.2 AL,
the world's first large-aperture
aspherical lens designed
specifically for SLRs. This lens,
extremely advanced in its time, far
outperformed other f/1.2 SLR lenses
of the era.
Realizing the potential market for
high-quality aspherical lenses,
Canon devoted intensive research to
the development of exclusive
manufacturing technologies. Unique
grinding and polishing methods were
perfected early on. However,
production costs were very high at
first, primarily due to the time
required to check each finished
lens for accuracy. But a
computerized checking method
drastically reduced the amount of
time while increasing the
reliability of the results. This
development enabled us to expand
the number of aspherical lenses in
the FD line.
Eventually, 5 formulas were
produced: 14mm f/2.8L, 20-35mm
f/3.5L, 24mm f/1.4L, 50mm f/1.2L,
and 85mm f/1.2L. Each lens offers
the fastest maximum aperture
available in its focal length,
while exceeding the optical
performance of all competitors.
In the EF line, ground and polished
aspherical elements are even more
important. Both the 50mm f/1.0L and
the 28-80mm f/2.8-4.0L use two
aspherical surfaces, while the 85mm
f/1.2L shares its single aspheric
optical formula with its FD
counterpart. The new
EF 20-35mm f/2.8L is the latest
entry into this elite group.
However, despite the reductions in
checking time, the ground and
polished method is limited to small
production runs. Therefore,
research continued on a way to
produce aspherical elements of
sufficient quality in even less
time.
In 1984, ' the big breakthrough
finally occurred. Canon's optical
designers developed a one-shot
glass molding process that could
produce exceptional quality in a
fraction of the time needed for the
ground and polished method. The
first lens to contain a
Canon glass-molded aspherical
element was the FD 35-105mm f/3.5-
4.5, which is still in the FD line.
This lens exhibited many desirable
characteristics, but most
impressively, when compared to the
previous FD 35-105, it , reduced the
weight from 600 to 344 grams.
Though not intended as an L-Series
lens, the new 35-105 exceeded the
optical performance of the lens it
replaced, while lowering the retail
price.
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