244 THE HASSELBLAD MANUAL
focusing screen. Do not just set it at infi nity if the subject is far away. The Carl Zeiss 250 mm Sonnar
Super Achromat, the 350 mm Tele Super Achromat and the 300 mm Zeiss Telephoto Powerpack
(TPP) in the V system are three such types. The latter consists of an FE Zeiss 300mm Tele
Superachromat, which is an apochromatic lens with some elements made from very spe-
cial types of glass. It comes with an apochromatic Apo-Mutar 1.7 Teleconverter specially
designed for this lens making it a 500 mm apochromatic lens. It is called a powerpack because
of the close focusing distance of 23 feet (7 m) and the large f/2.8 aperture, which is unusual
for such a long focal length especially in the medium format. Combined with the Teleconverter
is a 500 mm f/ 4.8 apochromatic lens. The lens is fi nished in a special type of silver gray anodiz-
ing with a high refl ectivity to reduce changes in temperature inside this lens which, in wildlife
and bird photography, can be exposed to bright sunlight over long periods of time.
Relative Illuminance
The corners of the image recorded by any lens receive somewhat less light than the center.
This loss of illumination can be caused by the lens design that limits the lens diameter to keep
lenses compact and lightweight. On wide angle lenses the cause is often found in the lens
barrel design where light rays that enter the lens at steep angles are cut off by components
in the lens barrel. Also on extreme wide angle lenses, the diaphragm opening that is circular
when seen from the front and allows a large amount of light to enter but becomes elliptical
and smaller when viewed from the side letting less light through the opening. Lens designers
try to keep the difference in illumination within acceptable levels. If this is not possible, you
can obtain a more even light distribution by reducing the illumination that goes to the center
of the image with a neutral density center fi lter placed over the lens. In the Hasselblad line,
this is necessary or recommended only with the Rodenstock lenses for the ArcBody and the
30 and 45 mm lenses of the XPan camera (for the 45 mm lens only when used at apertures f/8
or larger). On all other Hasselblad lenses, the corner illumination is within acceptable levels
so a darkening is never objectionable or even visible in the fi nal image.
The data for relative illuminance are published for all Hasselblad V and H system lenses
and are available from Hasselblad. Corner illumination improves when stopping down a lens
as can be seen by the diagram in Figure 14-7, in Figure 14.8 for the HC 150 mm lens with the
aperture stopped down to f/8 and, in Figure 14-6 for the HC 50–110 mm zoom lens wide
open and at f/8 at three different focal length settings.
Color Rendition
Color rendition in an image is determined mainly by the glass used in the lens. Individual mul-
ticoating of the different lens surfaces can also help to reduce variations between lenses.
Because sequences of images are frequently taken in the same location but with differ-
ent focal length lenses, matched color rendition in all lenses is important although variations
in a digital image can be corrected in after image manipulations. All lenses in the Hasselblad
system produce images with virtually identical color rendition even when comparing the V
system and the H system lenses.
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