Hasselblad Digital Camera, Руководство пользователя

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Digital Imaging with Hasselblad
35
to produce great image quality without the computer software. This topic is further discussed
in Chapter 14.
The HCD 28 mm wide angle (Figure 3-7) is one lens of this type in the Hasselblad line.
It is designed to cover only the digital sensor format of 36.7 49.0 mm, not the larger fi lm
format, which explains why this lens can only be used for digital recording and only with the
H3D and H3DII camera models. These cameras transmit the lens data, the focal length, the
aperture, and the distance setting to the computer which then makes the corrections. Future
HC lenses will undoubtedly be designed in the same fashion.
Figure 3-7
A 28 mm wide angle lens design . Lens design of HCD 28 mm extreme wide angle lens
for H3D and H3DII cameras.
Infrared Filter
Since digital sensors are very sensitive to infrared light, all Hasselblad digital cameras and digital
backs have an infrared fi lter in front of the sensor to eliminate the infrared and near-infrared
rays (IR) from reaching the sensor. Without the fi lter the digital image would be unusable. You
do not have to be concerned about this fi lter unless you plan to do infrared photography.
Digital cameras or digital backs cannot be used for infrared photography unless the fi lter
is removed, which can only be done at the Hasselblad factory and also involves re-calibrating
the sensor position as infrared rays form the image in a different plane. Some photographers
have used a camera with the IR fi lter removed for regular digital color photography by plac-
ing an infrared blocking fi lter such as BG 39 in front of the lens. The AF system in the camera
works as long as the fi lter is on the lens for regular photography. With the fi lter removed for
infrared photography, you must focus manually. If you plan to do extensive infrared work in
addition to “regular” photography, a logical solution that might come to mind is working with
two different digitals backs, one with and one without the infrared fi lter so you simply change
backs depending on the type of photography. In such a case, the back without fi lter may need
to be, and possibly can be adjusted for the focus shift, but at this writing, no specifi c details
are available. Check with Hasselblad before you decide on this solution. Using infrared fi lm in
a fi lm magazine is another solution but infrared fi lms are diffi cult to fi nd and also require very
special storage conditions and processing.
Infrared photography must be done through a fi lter that absorbs practically all visible
light. This can be a dark red fi lter or a true IR blocking fi lter which is opaque to the eye. This
fi lter on the lens makes it impossible to use the automatic focusing system. You must focus
the lens manually setting the distance opposite the infrared index on the lens.