Hasselblad Digital Camera - Page 260

Lens Characteristics and Specifi cations 245
Coating and Multicoating
Lens coating, invented by Zeiss in 1935, reduces light refl ections off a glass surface from
about 5 to 1%. In multicoating, invented later, each lens surface receives several layers of coat-
ing, each of a different thickness, to reduce refl ections from the different wavelengths of light.
This process reduces refl ections down to about 0.3%.
All Hasselblad H lenses are multicoated. All newer Hasselblad system lenses that carry a
red T engraving are multicoated with six or seven layers on each glass air surface. The 250 mm
Sonnar Super-Achromat is not engraved T because it has a one-layer coating as it was origi-
nally designed also for IR photography in the space program,
Coating and multicoating reduce the light that otherwise would be refl ected between
lens surfaces and eventually reach the image plane where it would cause fl are and reduce the
image contrast and color saturation. Disturbing light refl ections can also be created by the
interior of the camera body or the lens barrel. The interior of the H camera bodies and
the 503 model in the V system have a Palpas coating to reduce or eliminate refl ections. The
rear of the lens barrel in the latest lenses is also designed to reduce the risk of stray light
reaching the fi lm or digital sensor — a major difference between the CFi/CFE and earlier
types in the V system.
Lens Shades
Multicoating of lenses has not reduced or eliminated the need for lens shades. Shades serve
a different purpose than multicoating. Multicoating and coating the interior camera body
reduces refl ections from the light that actually goes through the lens to form the image in the
Figure 14-7 Relative illuminance. The relative
illuminance shown with the aperture wide
open (bottom line) and closed down two f
stops (top line). The image height is again
on the horizontal axis with the center at
the left and the corner at the right.
f/3.2
f/8
0
01020
Image height (mm)
30
Relative illumination
0.2
0.4
0.6
0.8
1.0
Figure 14-8 Illumination at different
apertures. Illumination diagram for the
HC 3.2/150 mm lens shows that corner
illumination improves when the aperture is
stopped down to f/8.