likely that sharp focus and size are not being simultaneously
(4) Lower focusing glass in position, open shutter,
and switch on arc lamps.
(5) Examine image of grid or square on focusing
If counter readings are in close
glass. It should be sharply defined when viewed without or with
agreement at same size, and increase
the focusing magnifier. (If not, see d. below.) Next square up
in variance for increasing ratios of
and center the image on the grid of the focusing glass by use of
enlargement or reduction, it is possible
oscillating knob (4, fig. 4-2) and lens control knobs (5 and 10,
that the focal length of the lens differs
fig. 1-4). The image should exactly match the corresponding
from that given in the chart. This may
square on focusing glass within 0.005 inch tolerance (that is,
be due to loosened lens elements (for
the thickness of the grid lines) and the lines should overlap or
which condition lens must be sent back
touch. If not, see d. below.
(6) Repeat for several other ratios such as one half
adjustment), or to a curvature of the
size (0.50), and twice size (2.00). If images are sharp and in
main camera rail, that can be checked
size agreement with corresponding grid square, the camera is
with a long precision straightedge or
accurately focused to accord with the chart.
calibrated precision level. If rail is
curved or otherwise distorted, it must
(7) Repeat checks with secondary
be returned to true before accurate
determine agreement with its focusing chart.
camera reproduction can be achieved.
e. Out-of-Focus Conditions.
The camera specifications require that
the camera copyboard maintain its
(1) If sharp focus is not obtained, note if image is
alignment and parallelism throughout
slightly out-of-focus (can be seen but not distinctly) or
its movement to within 0.005 inch.
completely out-of-focus (no resemblance of an image visible).
(2) If slightly out-of-focus, this may be due to the
(3) If image
condition may be due to:
(a) Incorrect counter settings, or by not
(a) Wrong counter readings.
taking up play. Counters must always be set with decreasing
readings down to number desired.
(b) Wrong lens focusing chart.
against lens number.
(b) Allowance not made for copy thickness.
Copy thickness must be added to copyboard reading.
(c) Counters incorrectly set.
trammeling distances, or adding distances, or allowances for
(c) Disturbance of optical planes. Check that
nodal corrections, or for lens constant.
copyboard rests solidly against its stops, that lens is screwed in
firmly and seats on its ring in the lensboard, and that focusing
(d) Camera calibrated to secondary instead
glass rests solidly against the magnetic latches.
of principal lens.
(d) If the above inspection does not reveal
the cause of the out-of-focus condition, the trammeling
characteristics altered during lens repairs (to remove scratches
measurements may have been in error, as any lens deviations
or other defects) by manufacturer.
would have been compensated for in the original calibration of
(4) Check all physical conditions listed above, other
the focusing chart. Sharpen up focus
by moving the
than internal lens inspection, to ascertain and correct existing
copyboard to or away from the lens and then check size ( ara
cause. If this cannot be determined, focus camera visually
2-36.f.). When both exact size and focus are obtained visually,
note the difference between the actual counter readings and
readings for several ratios of reproduction (d. (2) (d) above) to
those on the chart. Repeat this test for other ratios such as
determine if counter readings are displaced. If sharp focus
one-half size and twice size, and again compare readings. If all
cannot be obtained at all, or if some obvious lens defect is
show approximately the same difference, the counters have not
evident such as loose elements on shaking lens, or injuries that
been set right, and should be reset by accurate measurement if
mar lens surface (chips, etching due to chemicals or fungus, or
possible, or by averaging the differences obtained and then
frosting due to improper cleaning of the lens), the lens must be
changing the counter readings to bring them in agreement with
sent to an optical technician for inspection and subsequent
image size and focus. (Differences should agree with each
correction or replacement.
other within three or four hundredths of an inch. If more, it is