Advanced Photography Course

From each processing run, you should plot the

gamma and on the chart. You should write

other data, such as processing time (or machine
speed), temperature, rate of replenishment, and amount
of film processed, on the control chart. After
connecting the dots, you will know what the processor
is doing and the direction in which the process is
going.

Remember that the existing tolerance or control

limits, once set, should not be left there indefinitely.
You should continually strive to improve the degree
of control and, to do so, reestablish closer control
limits periodically.

The amount of information you can plot on

control charts depends on several factors that may
include, but are not limited to, the following:

The product quality required

The equipment available

Personnel available and trained for QA duties

You are not expected to monitor all the variables

that are listed. Also you are not limited on what you
can monitor. These decisions depend on the
capabilities of each imaging facility, and they change

periodically. Figure 2-13 shows the way a control
chart might look. It is an example only and should
not be used to establish control parameters in your

imaging facility.

Before control charts are established, you must

have a standard or starting point for each of the

variables you intend to measure. These standards are

derived by sensitometric or chemical tests over a
given period of time or, in the case of color
processing,

are provided by the manufacturer.

Generally speaking, when these tests are conducted
within an imaging facility, they are to be performed

by a PH with a background in photographic quality
control (NEC 8126) or by a PH with extensive
on-the-job training in QA. These specialists analyze
the data collected over the test period, apply statistical

formulas, and arrive at workable standards or means
and upper- and lower-control limits. Therefore, in the

rest of the discussion, assume that these standards
have already been established. A word of caution,
however, the chart, plot, and curve illustrations that

follow are presented as examples only. They should
not be used as a basis for the QA program in any lab.

PLOTTING GAMMA OR CI ON
A PROCESS-MONITORING
CHART

As explained previously, gamma and CI can be

computed from the information plotted on a
characteristic curve. Successive values are then
plotted on control charts.

When gamma plots on a control chart beyond the

control limits, several causes may be indicated, some
of which include the following:

The developer is being over- or under-

replenished.

The film was over- or underdeveloped.

The processing temperature was too high

or too low.

PLOTTING HIGH DENSITY
ON A PROCESS
CONTROL CHART

A density step from a processed control strip is

plotted as the high density (HD) on a control chart.
The specific step number is determined in tests as
discussed previously.

Once this step has been

determined, it should be used for each reading or plot
until a new standard or mean is determined. For the
purpose of our example, we are plotting or measuring
step 16 as high density.

The following factors can cause the high density

to be out of control:

Variations in the processing temperature

Variations in the processing time or machine
speed

Over- or underreplenishment

PLOTTING LOW DENSITY ON
A PROCESS CONTROL CHART

As with high density, low-density (LD) readings

should also be taken from a predetermined density
step of a control strip.

2-24

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Advanced Photography Course

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DOFMaster for Windows On-line Depth of Field Calculator DOFMaster for Mobile Devices On-line Depth of Field Table Hyperfocal Distance Chart Articles FAQ Recommended Books Support Contact Links Home As an Amazon Associate I earn from qualifying purchases.	contents <- previous page next page -> From each processing run, you should plot the gamma and on the chart. You should write other data, such as processing time (or machine speed), temperature, rate of replenishment, and amount of film processed, on the control chart. After connecting the dots, you will know what the processor is doing and the direction in which the process is going. Remember that the existing tolerance or control limits, once set, should not be left there indefinitely. You should continually strive to improve the degree of control and, to do so, reestablish closer control limits periodically. The amount of information you can plot on control charts depends on several factors that may include, but are not limited to, the following: The product quality required The equipment available Personnel available and trained for QA duties You are not expected to monitor all the variables that are listed. Also you are not limited on what you can monitor. These decisions depend on the capabilities of each imaging facility, and they change periodically. Figure 2-13 shows the way a control chart might look. It is an example only and should not be used to establish control parameters in your imaging facility. Before control charts are established, you must have a standard or starting point for each of the variables you intend to measure. These standards are derived by sensitometric or chemical tests over a given period of time or, in the case of color processing, are provided by the manufacturer. Generally speaking, when these tests are conducted within an imaging facility, they are to be performed by a PH with a background in photographic quality control (NEC 8126) or by a PH with extensive on-the-job training in QA. These specialists analyze the data collected over the test period, apply statistical formulas, and arrive at workable standards or means and upper- and lower-control limits. Therefore, in the rest of the discussion, assume that these standards have already been established. A word of caution, however, the chart, plot, and curve illustrations that follow are presented as examples only. They should not be used as a basis for the QA program in any lab. PLOTTING GAMMA OR CI ON A PROCESS-MONITORING CHART As explained previously, gamma and CI can be computed from the information plotted on a characteristic curve. Successive values are then plotted on control charts. When gamma plots on a control chart beyond the control limits, several causes may be indicated, some of which include the following: The developer is being over- or under- replenished. The film was over- or underdeveloped. The processing temperature was too high or too low. PLOTTING HIGH DENSITY ON A PROCESS CONTROL CHART A density step from a processed control strip is plotted as the high density (HD) on a control chart. The specific step number is determined in tests as discussed previously. Once this step has been determined, it should be used for each reading or plot until a new standard or mean is determined. For the purpose of our example, we are plotting or measuring step 16 as high density. The following factors can cause the high density to be out of control: Variations in the processing temperature Variations in the processing time or machine speed Over- or underreplenishment PLOTTING LOW DENSITY ON A PROCESS CONTROL CHART As with high density, low-density (LD) readings should also be taken from a predetermined density step of a control strip. 2-24 contents Advanced Photography Course <- previous page next page ->	As an Amazon Associate I earn from qualifying purchases.
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