Operating Instructions—C-30B Camera
Light Streaks on Picture
1. if light leaks in the bellows between the shutter box
and camera back, see your local Tektronix Repräsent
ative for repair.
2. The light seal between camera and oscilloscope may
be faulty.
3. Rollers in the Polaroid camera back may be dirty.
4. Polaroid film pack was handled too roughly during
loading.
Fogging on Picture
1. Scale illum ination control is set too high.
2. Light-struck or bad film .
3. Film exposed to light during loading.
Trace or External Graticule in Focus, But Not
Both
1. Use f-STOP setting larger than f/4 when photo
graphing an external graticule.
2. Camera should be refocused because of object-to-i
mage ratio change.
Some Portions of Photographed Signal Appear
Brighter Than Others
Use an exposure time long enough to allow several
sweeps to occur.
ELIMINATING PARALLAX AND
FOCUSING DIFFICULTIES
Tektronix Instruments w ith the internal "no parallax"
graticule and variable edge-lighting w ill have no parallax
Problems and therefore no focusing difficulties.
On some instruments the trace and graticule are not in
the same plane, resulting in parallax. This makes it im-
possible to simultaneously obtain good focus on both the
trace and graticule at f-STOP settings below f/4 . Both of
these difficulties can be eliminated by either of two
methods. Both methods involve double exposing the film .
First Method
Set up the instrument display as usual and focus the
camera on the trace. Turn the graticule intensity to min-
imum and make the first exposure on the trace only. Then
increase graticule intensity to its former brightness and set
the camera lens to its smallest lens opening (largest f-STOP
number). Readjust the shutter speed to compensate for the
smaller lens opening. Turn down the crt trace intensity and
make a second exposure of the graticule only. The resulting
Photograph, due to the greater depth of field when making
the graticule exposure, w ill have some parallax error be
tween graticule and trace, but both the graticule and trace
w ill be in proper focus. Care must be taken in using this
method to ensure that the Position of the film for the
second exposure is exactly the same as for the first
exposure.
Second Method
Set up the instrument display as usual and focus the
camera on the trace. Turn the graticule intensity to min-
imum and make the first exposure on the trace only. Then
increase the graticule intensity to its former brightness and
refocus the camera on the graticule. Turn down the crt
trace intensity and make a second exposure o f the graticule
only. The resulting photograph, due to refocusing between
exposures, w ill have no parallax error between graticule and
trace; both the graticule and trace w ill also be in proper
focus. Care must be taken in using this method to ensure
that the Position of the film for the second exposure is
exactly the same as for the first exposure.
EFFECTS OF THE f-STOP SETTING
ONTHE DEPTH OF FIELD
The depth of field defines the ränge of distance from the
camera lens over which objects w ill still be in focus at the
film plane. As shown in Figure 2-13(A), a wide aperture
opening (corresponding to a small f-STOP setting) permits
light rays to pass through the outer extremities of the lens.
These peripheral rays converge rapidly to focus on the film
plane. Consequently, when the distance from the lens to
the object is changed slightly, the image on the film
defocuses quite rapidly due to the sharp convergence of the
light rays.
In Figure 2-13(B), the same lens is shown w ith a smaller
aperture (corresponding to a larger f-STOP setting). Now
when the object distance is changed, the image defocuses
much more slowly due to the slower convergence of the
light rays.
Accordingly, setting the f-STOP control to the largest
number that w ill still provide sufficient film exposure w ill
help provide the sharpest image.
2-16
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Содержание C-30B
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