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Certainly the most significant part of the Minox is the
optical system. I say "system" because a change in any part
seems to diminish the performance of the original ingenious
design. The notion that a camera can produce sharp images
from 8 inches to infinity is by itself unique. The ability
to produce sharp images of objects in the range of 6 feet to
infinity adds icing to the cake. Together, these two
features make the Minox one of the most useful cameras
available. BUT - and it is a big "but" - one must pay
attention when focusing.
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Several factors affect the quality of
the image.
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1.
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Distance of
NEAREST object from the camera,
Distance of FARTHEST
object from the
camera,
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2.
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Accuracy of
focus
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and not the
least important -
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3.
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Amount of
enlargement of the final
print!
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Each camera (Minox, Leica, Nikon,
Rollei) has an ASSUMED enlargement factor
for which the depth-of-field marks are
inscribed. Reference to computed tables,
or the calculation of Depth of Field
tables will reveal the print size
upon which the inscribed marks indicate a
satisfactory result. For the Minox, the
mark below the focusing knob covers a
distance of approximately 7 feet to
infinity, which will yield a "sharp" print
of approximately 5x7 inches.
As the illustration shows, the
depth-of-field marked on the camera body
does not change, representing smaller and
smaller image ranges as the focusing
distance decreases.
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Fig. A
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If a print of larger size is desired, the
range should be reduced. Doubling the print size
will cut the range of sharpness in half. Thus,
rather than a range of from 7 feet to infinity, the
depth-of-field (range of apparent sharpness in the
print) will cover only 14 feet to infinity. This
reduction in depth-of-field applies to all focused
distances, thus reducing the closeup range from 8 -
9 inches to 8 - 8.5 inches.
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 If the small bar
below the dial represents the range of acceptable
sharpness, and if the infinity mark is placed in
the center thereof, then, in this illustration, the
range of acceptable sharpness extends from
approximately 12 feet to infinity. With the dial
set as shown in Fig. A above, the range is
considerably greater. In Fig. A, the focus is set
at the HYPERFOCAL distance,
the point at which, when focused, the lens will
provide the widest possible range of acceptable
sharpness INCLUDING
infinity. Except in cases where there is no near or
intermediate subject matter, it is of little value
to focus on infinity. BUT, it is also useful to
know where YOUR camera is focused at the different
settings, so some testing might be worthwhile.
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Coupled with depth-of-field considerations are those
of Diffraction, which also causes a
blurring of the image. There is a maximum enlargeability for
each f/stop, after which diffraction can cause as much
damage as improper focusing.
Maximum enlargeability for blue light at f/3.5 is 183,
and 105 for red light. As these are theoretical values, it
is suggested that they be halved, yielding 92 and 52. Since
fuzzy red light is not of much value even with sharp blue
light, 52 is probably a good value to use. A 52x enlargement
from an 8mm x 11mm Minox negative yields a 16 x 23 inch
print - far beyond the capability of most film - AND the
ability of the photographer to focus accurately and control
the other factors that degrade image quality.
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