Darkroom Fog and Viewbox Illumination Check

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Darkroom Fog and Viewbox Illumination Check
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Darkroom Fog Check

• EQUIPMENT NEEDED
• X-ray film
• Clock or stopwatch
• Densitometer
• Penetrometer
• Darkroom
• Radiographic room

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Turn off all of the safelights and overhead
lights in the darkroom. After eyes are adjusted
to the darkness (about 5 minutes), look for any
sources of light that you can find. Pay
particular attention to the seals around
processors, pass-boxes, darkroom doors, and so
on. Suspended ceilings can leak light from the
surrounding rooms. Make note of any light leaks
and indicate them in the analysis portion of this
experiment. Turn the safelights back on.
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Remove an 8 ? 10 inch cassette from the passbox,
and take it into one of the radiographic rooms.
Place it in the center of the x-ray table at a
40-inch (100-cm) source-to-image distance (SID).
Place a penetrometer in the center of the
cassette, aligning the long dimension of the
wedge with the long axis of the cassette.
Collimate the light field to the edges of the
step wedge. Expose the cassette using
approximately 70 kilovolts (peak) (kVp) and 5
milliamperes-second (mAs) or enough to give the
center step of the step wedge pattern an optical
density of approximately 1.0.
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Enough to give the center step of the step wedge
pattern an optical density of approximately 1.0
Approx. 1.0
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Return the cassette to the darkroom and remove
the exposed film from the cassette. Lay it on the
counter and cover one half of the film with a
sheet of cardboard or other opaque material.
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Expose the film to normal safelight conditions
for 2 minutes and then process the film.
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Place the film on a viewbox illuminator and
observe if there is a defined line or break
between the halves. Use a densitometer to record
the optical density of each half. Determine the
maximum density difference by subtracting the two
optical density values for each step. The step
with the greatest maximum density difference
indicates the darkroom fog level. Record all data
on the Safelight Test form.
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Viewbox Illuminations

• EQUIPMENT NEEDED
• Photometer
• Various department viewboxes

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Photometer
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Set the photometer to measure illumination in
candles (cd) per square millimeter (nit). Place
the aperature opening 9 inches away from the
center of the viewbox illuminator and record the
reading on the data page.
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Mentally divide the view box into quadrants and
take a light measurement from the center of each
quadrant. Record the readings on the View Box
Quality Control Test Form. Compare each of these
values with each other and with that of the
center obtained - These values should be within
10 of each other.
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Illuminationmax Illuminationmin Illuminationmax
Illuminationmin
100
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Repeat Steps 1 and 2 for the other viewboxes
within your particular bank. Using the center
readings, determine the maximum variation in
brightness among the viewboxes in a particular
bank. These values should be within ? 15 of each
other.
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Set the photometer to record illumination in lux
or foot-candles (ft-c). Measure the ambient light
levels by turning off the viewbox, but leave on
all of the overhead room lights that are normally
in use. Place the light meter 9 inches away from
the viewbox front and record the reading (even
though the viewbox is off). The maximum ambient
light should be about 320 lux or 30 ft-c.