Model 196A Section VI
Paragraphs 6- 18 to 6- 19
focusing procedure, using less specialized equipment j. Tighten the right-hand bottom camera mounting
is given in paragraph 6-19. screw until it is just snug.
NOTE k. Check the bottom left and the upper right corners.
A change in lens-to-object distance from the If they are not in focus, rock the camera-back from
normal distance of 3/8 inch from the camera upper right to bottom left slightly to find the area of
nose will cause a change in image-to-object best focus.
ratio. If it is desired to bring this ratio to m. Recheck the focus on all four corners and tighten
an exact value refer to paragraph 6-13. all four camera mounting screws securely.
6-18. PROCEDURE. If malfocus is suspected, first 6-19. ALTERNATE PROCEDURE. The following is
check to see that the cathode ray tube is positioned an alternate procedure for resetting focus using less
against the graticule. If the focus still seems bad, specialized equipment.
perform the incoming check given in paragraph 2-3.
It is extremely important that these factors be checked NOTE
first, since refocusing is a difficult procedure. To
refocus the 196A, proceed as follows: This procedure should be used only to provide
temporary settings until a more accurate
setting is obtained using the procedure and
a. Mount the camera on the special setup described equipment similar to that in paragraph 6-18.
in paragraph6-9 and figure 6-1. Make sure the camera
nose is against the plexiglass. The 100-watt diffused
light source should be mounted so it shines through a. Mount the 196Aon an oscilloscope having the de-
the amber plexiglass. sired object distance.
b. Connect a 10 kc sine wave to the vertical ampli-
b. Set the aperture to f/l. 9 and the shutter speed fier, and adjust the sweep length so that there are
to "T". four to six cycles per centimeter.
c. Actuate the cable release once (the shutter should c. Set the aperture to f/l. 9 and the shutter speed
now be open). to "T. Actuate the cable release. The shutter should
now be open.
d. Open the camera cover and bridge and place the d. Open the outer and inner doors and place the plexi-
piece of ground glass in the focal plane. glass or ground glass on the image plane.
NOTE NOTE
Make sure the frosted side is toward the lens. Make sure the frosted side is toward the lens.
e. Turn on the diffused light source. e. Using the 1/4-inch box wrench, loosen the four
camera mounting screws (number 1 in figure 6-3).
f. Using the 1/4-inch box wrench, loosen the four
camera mounting screws (number 1 in figure 6-3). f. Dim room light or place a black cloth over both
your head and the camera.
g. Using the magnifying glass, look at the presenta-
tion on the ground glass in the upper left-hand corner. g. Adjust the oscilloscope amplitude and vertical
Movethe camera-back slightly to find the area of best position so that the sine-wave presentation is centered
focus for that corner. and is approximately 10 cm high.
h. Tighten the camera mounting screw over that h. In the areas that are out of focus, the vertical
corner until it is just snug. lines of the sine wave will appear to "run" together
instead of appearing as separate lines.
i. Now check the area in the right-hand bottom of
the glass. Again, move this corner until it is in good i. Adjust the camera back, usingthe procedure out-
focus. Recheck the upper left-hand corner to make lined in paragraph 6-18, steps f through m, until opti-
sure it is still in focus. mum focus is attained. Do not use the magnifying glass.
01038- 1 6- 5 |
ACEC
