Far focusing distances yield more depth of field than near focusing distances.
Control of Depth of Field
The depth of field-dependent on the distance actually focused at, the aperture employed and the focal length of the
lens -- has to be ascertained from case to case. As the Retinette lenses are not interchangeable, the factor of the
focal length need not worry us. There remains the interplay of aperture and focusing distance. Their effect can be
read off a depth of field calculator engraved on the front of the shutter of the Retinette I, IA, IB and earlier models.
The automatic Indicators of the Retinette II and IIB models directly show the zone of sharpness on the focusing
scale with the distance set to the actual index line; everything is sharp from one pointer to the other. The pointers
move in or out automatically when the aperture is varied.
With the Retinette I and earlier models, the depth is read off separately for; each aperture at any given distance
setting.
Turn the focusing mount of these Retinette models until one of the figures on the distance scale corresponding to
the subject distance (for instance, 8 ft.) is opposite the indicator. Let us assume that we are working at f5.6. The
two lines marked 5.6 to either side of the Indicator are now opposite approximately 6 and 11ft. respectively, so our
depth of field extends from 6 to 11 ft. When working with the lens set to the same distance but with aperture f3.5,
the depth only extends from about 6½ to 9 ft., while at f11 we have a sharp zone extending from just under 5 ft. to
nearly 18 ft. Note how we can control the area of sharpness merely by changing the aperture.
So the stop (aperture) is one of the variables by which a convenient zone of sharpness can be obtained. The other
one is, of course, the distance setting. Let us watch the index lines leading from, say, aperture f5.6 while we set the
distance indicator first at 5 ft., then at 8 ft. and last at 25 ft. We learn that in the first case the depth of field
stretches from 4½ ft. to 6 ft.; In the second case from 6 to 10 ft.; and in the last case from 13 ft. to infinity. So we
see confirmed that the depth of field grows as we set the lens at distances farther and farther away from the camera
-- and incidentally may conclude that the depth of field in front of the focused distance is always more limited than
the depth gained behind it.
The comparative shallowness of the depth of field in front of the focused distance will sometimes make it necessary
-- e.g., in landscape photography, where the subject may have to include much foreground -- to set the lens nearer
than the main point of interest lies, in order to gain additional sharpness towards the foreground while covering the
main point of interest by the depth of field behind the focused distance. This trick, however, must be used with
moderation. It should be recalled that the widely held idea that everything is equally sharp within the depth of field
area and completely unsharp outside its limits is quite wrong. There is a gradual decline of sharpness even within the
depth of field area. Critical "pin-point" definition can be expected only in the plane actually focused. So care should
be taken to place the focus as near as possible to the spot on which the greatest sharpness is required. Thus in the
case of distant landscapes use should not be made of the hyperfocal distance (described on page 42) if the
sharpness is required in the far distance; focusing at the far distance will give better results.
When a lens is focused on such a distance that the depth of field just reaches the far distance (Infinity) then the lens
is focused on the "infinity-near point" or hyperfocal distance. This adjustment of focus is advisable when it is desired
to secure adequate sharpness from the farthest distance to as far as possible in the foreground, rather than extreme
sharpness in the far distance only.
DEPTH OF FIELD
