The Superwide Cameras 189
D2
D3
Light ray path
through air
Light ray path
through glass
D2 D3
Figure 11-2 Path of light rays to the digital
sensor. Light rays at the edges hit the glass
surface at an oblique angle and need to
travel a different distance than they do in
fi lm photography without the glass.
Resulting plane of sharpness for Biogon 38 due to spherical
aberration introduced by the IR filter and cover glass
200 μm
Figure 11-3 Plane of sharpness. The curvature
in the plane of sharpness of the Biogon
38 mm due to the spherical aberration
introduced by the IR fi lter and cover glass in
front of the digital sensor.
Figure 11-4 The Biogon in digital recording. The Biogon 38 mm shown with the 36.7 49 mm
sensor and the cover glass and IR fi lter in front of the sensor.
results in a curved image plane (Figure 11-3) that creates the unsharpness on the edges of the
image. Stopping down the lens aperture improves the quality but not to the point where it
can be considered good enough for the high quality images demanded in architectural and
aerial photography. The loss of quality is most noticeable on the large 36.7 49 mm sensor
where the large angle of view of the Biogon 38 mm is most benefi cial. On smaller sensors, the
angle of view, and thus the benefi ts of the 38 mm focal length are reduced.
Consider the HCD 28 mm lens for high quality digital work on H3D and H3DII cameras.
This lens has a diagonal angle of view that is even larger than the 38 mm Biogon, and the
cover glass and IR fi lter in front of the sensor were taken into account in the lens design.
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