Leica APO-TELYT-R, APO-ELMARIT-R manual Chapter Leica R-Lenses

Chapter 3

Leica R-Lenses 1

Telephoto lenses have a long tradition at Leica. The first 20 cm f/4.5 Telyt lens was introduced as long ago as 1935 for the Leica rangefinder camera. An additional mirror reflex housing was required for the accurate determination of the field of view and the focus. This 200 mm lens was designed for landscape work, animal photography and sports photography. It is intere- sting to read that sports photography in modern large stadiums was only possible at longer distances, and this required the long lengths. The lens was also quite suitable for portrait stu- dies, the classical head-and-shoulders type.

The Telyt was three times as expensive as the standard 50 mm f/3.5 Elmar lens, and with the mirror reflex housing it was five times as expensive.

The design was a true telephoto design: the total length was about 0.8x the focal length. A long focus lens is simply a lens with a longer focus than a standard lens (more than 2x). Exam- ples: 90 mm Elmar, 105 mm Elmar, 135 mm Elmar lenses. There are also lenses with a telescopic construction: example: 800 mm f/6.3 Telyt-S. This type of lenses has been in use since 1700. The very first telephoto lens was introduced in 1891 by the English firm of Dallmeyer. By now this design is 112 years old, and it was only recently upgraded to a very high opti- cal performance, not in the least by the efforts of Leitz.

The first 180 mm f/2.8 Elmarit-R lens for the Leica R-System was introduced in 1967 as a counterpoint to the 180 mm f/2.8 Zeiss Sonnar lens that was introduced in 1966 for the Zeiss Contarex system. With five elements in four groups, it was a state-of-the art design, but the Elmarit lens weighed 300 grams (10.6 ounces) more than the Sonnar lens. The price-ratio to the standard lens was now 2:1. The second version (of 1980) weig- hed only 750 grams (26.5 ounces) and it had a somewhat bet- ter performance. Gradually, 180mm lenses were beginning to be used for hand held dynamic photography when a tripod would be a hindrance in following rapid movements of the sub- jects.

spectrum. 'Secondary' may also be read as 'residual chromatic errors'.

A 180 mm telephoto lens has a magnification factor of 3.6x compared to the standard lens and this means that the residual chromatic errors will also be enlarged 3.6 times. At the start of the seventies it became clear that the performance of these long focus lenses lagged behind that of wide-angle and normal lenses and therefore needed improvement. New glass types with high refractive indices and anomalous (non-linear) disper- sion were needed.

Light waves are refracted by different amounts depending on their wavelengths. The power of the lens depends on the wave- length. This is called dispersion. Normally the power will increa- se continuously with decreasing wavelength. If the power chan- ges abruptly, this is not normal or non-linear or anomalous.

New glasses with these characteristics were developed in the former Leitz glass laboratory and later produced by Schott, Corning and others. By means of an appropriate optical design, the secondary spectrum could be reduced to so small an amount that for all intents and purposes an image free of color defects could be created. This state of correction is known as apochromatic correction.

The Achilles heels with telephoto lenses are the chromatic
errors and the size of the secondary spectrum or chromatic dif-	Erwin Puts
ference (typically 0.002 times the focal length [F]).	Leica Camera AG
Visible light is composed of wavelengths with frequencies from
short waves of about 380 nm (nanometers) to long waves of
about 780 nm. Lenses are generally corrected for two specific
wavelengths: 643 nm (red) and 479 nm (blue), so that both
these wavelengths will focus on the same image plane.
This plane is located behind the plane where the third impor-
tant wavelength (green, 546 nm) is focused. The longitudinal
difference between these two locations is called the chromatic
difference. If only two wavelengths are focused in the same
plane, all the others will focus somewhere else on the optical
axis. The sum of these aberrations is called the secondary