Optical considerations | Leica APO-TELYT-R, APO-ELMARIT-R instruction

Chapter 3

Leica R-Lenses	5

Atmospheric turbulence and heat waves can destroy the image quality at these large magnifications and one needs a skylight filter with color film and a medium orange filter with black-and- white film.

The discussion often arises as to whether a lens can be too sharp, a question that is certainly relevant for both of these lenses. In many discussions, sharpness and contrast are seen as the destroyers of subtle tonal values.

This idea is associated with the effects of gradation of films and papers. A steep gradation of a film or a paper with a high contrast will accentuate small differences in brightness and also reduce the number of tonal shades of the overall tonal range. But these properties cannot be transferred to the optical sharpness or modulation transfer.

Any lens should generate an accurate image of the subject. Every detail (subject outline, textural detail, tonal value) is a composition of very small point images of different brightness. If we have a lens that is free from aberrations, every point will be reproduced on film exactly as it is in the real world.

A lens with optical aberrations will reproduce these points with some blur and the small differences in brightness will also be diffused. The better the lens, the more accurate the image reproduction and the finer the brightness differences that we can discern.

For the first time, chromatic aberrations (color fringes) could be reduced to negligible amounts. Multi-layer coating was used sparingly, as these layers often create more problems than they solve. Especially with strongly curved surfaces and with glasses with high refractive indices, a uniform thickness over the entire surface could not be guaranteed.

It seemed impossible, but with the 180 mm f/2.8 Apo-Elmarit-R lens, image quality was improved significantly. With seven ele- ments in five groups, its design is totally different from that of the 180 mm f/3.4 lens, also with seven elements in four groups.

The 280 mm f/4 Apo-Telyt-R lens can be combined quite effec- tively with the Macro-Adapter-R. Then you can take pictures at a distance of one meter (3’ 3 3/8”) from small animals that do not let you approach too closely, like frogs. You may even com- bine the Macro-Adapter-R and the Apo-Extender-R. This is also true for the 180 mm f/2.8 Apo-Elmarit-R lens.

You might even use two Macro-Adapters together.

The only recommendation I can give is to be willing to experi- ment and investigate which combination best suits your needs.

__ Optical considerations

The basic design of a telephoto lens consists of a converging front lens with a positive focal length and a diverging second lens with a negative focal length. The main optical problems with telephoto lenses are distortion (solved quite early), secon- dary spectrum and the longitudinal chromatic errors.

The first 180 mm lenses from Leitz had five elements in four groups. Their design was derived from the 135 mm lenses. A low number of elements reduced flare, but it also limited the optical correction a bit. Chromatic correction was not optimal and overall contrast was on the low side. Image quality was quite good, especially because now one needed a lower magni- fication of the negative. The breakthrough came with the 180

mmf/3.4 Apo-Telyt-R lens, a design that used new types of optical glass.

Maximum quality is already reached at full aperture. From the center to the edge of the image, a resolution of extremely fine details with high micro-contrast is ensured. Especially with fashion- and beauty photography, where hyper-realistic images are required, these lenses are ideal. From a lens tester’s point of view, the 180 mm f/2.8 Apo-Elmarit-R lens is not a challen- ging lens: there is hardly a point to criticize! Thanks to its floa- ting element design, performance in the close-up range is excellent.