Leica THAMBAR-M 90 f/2.2 Instructions Manual page 6

EN
STRUCTURE OF THE LENS
In the Leica Thambar-M 90 f/2.2, the rotating front part of the lens mount
contains the aperture setting ring (3), the knurled gripping ring for distace
setting (4) and the aperture (3b) and distance scales (4a). The index for distance
setting (5), the depth of field scale (6) and a red dot for lens change (7) are
located on the fixed rear part of the lens mount. A 6 bit lens identification bar
code (8) is situated on the bayonet flange. It relays lens data to the camera
body so the exposure metering system of digital Leica M models can be calibrat-
ed. The information is also used to custom-optimize image data according to the
respective lens.
USE WITH/WITHOUT CENTER SPOT FILTER
Due to its special optical properties, the degree of soft-focus of the Leica
Thambar-M 90 f/2.2 can be controlled to a certain extent. Without the center
spot filter (2) supplied, this is done only with the aperture; the scale with the
white values applies in this case. When the aperture is open, the soft focus
effect is very marked; with aperture values of around 9 and higher, the lens
provides its highest contrast reproduction. This is due to the fact that then only
the central area of the lens with the best image aberration correction is used.
An even greater soft focus effect can be achieved with the center spot filter sup-
plied: Since the opaque spot in the centre of the aperture blocks the central
beam, the image is largely generated only by a ring of beams, and consquently
only with the area of the lens that is primarily responsible for the soft focus
effect. In this case, the aperture scales with the red values applies. The higher
values of the larger apertures (in comparison to those on the white scale) take
account of the light loss through the blocking of the central beam. This scale
reaches only up to 6.3 since the simultaenous use of even smaller aperture
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