Hasselblad Digital Camera, Руководство пользователя

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Close-Up Photography on Film or Digital
355
usually means covering a specifi c size area so the magnifi cation is predetermined. You can, there-
fore, increase depth-of-fi eld only by closing the lens aperture (or covering a larger area which
means a lower magnifi cation). Depth-of-fi eld becomes about twice as large when you close the
aperture two stops. At a specifi c magnifi cation, depth-of-fi eld is the same regardless of the focal
length lens you use but unlike at longer distances where about one-third of the depth-of-fi eld
is in front and two-thirds behind the subject, it is more evenly divided at close distances. But as
always, the blur beyond the depth-of-fi eld falls off more rapidly with a longer focal length lens.
Because depth-of-fi eld is determined only by the magnifi cation and the lens aperture, we
can make a simple depth-of-fi eld chart that applies to all cameras and lenses. The chart in
Table 19-1 is based on an
f /11 lens aperture. Column A is for general close-up work based on
a circle of confusion of 0.06 mm (
1
/
400
in.), which is used for the calculations of the depth-
of-fi eld scales in the V system. Column B is for critical work based on a circle of confusion of
0.03 mm (
1
/
800
in.). Depth-of-fi eld scales and charts in the H system are based on a circle of
confusion of 0.045 mm (
1
/
600
in.).
Table 19-1
Depth-of-Field at Various Magnifi cations
Total depth-of-fi eld in mm at f /11
Magnifi cation A B
0.1 100 50
0.2 30 15
0.3 15 7
0.5 6 3
0.8 3 1.5
1 2 1
1.2 1.5 0.7
1.5 1 0.5
2 0.8 0.4
3 0.4 0.2
WORKING WITH EXTENSION TUBES
Extension tubes of different lengths can be used for close-up photography with the H and
V system SLR Hasselblad cameras for digital imaging or fi lm photography. The tubes have no
optical components and are mounted between the camera and lens to increase the image dis-
tance. You can uses one tube or combine them for a greater extension.
A few basic facts about extension tubes are listed below.
●
The longer the tubes with a particular focal length lens, the closer the distance at which you can
photograph; consequently, the smaller the area coverage and the higher the magnifi cation.
●
Extension tubes of a specifi c length give a smaller area coverage and a higher magnifi cation with
shorter focal length lenses than with lenses of a longer focal length.
● You can cover the same area with a shorter focal length lens and a shorter tube or with a lens
of longer focal length combined with a longer tube. The two differ in the working distance, the
background coverage, and background sharpness.