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Mitsubishi Electric KD Series User Manual page 24

Contact image sensor, web surface inspection
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2-3 Definition
【Depth of Focus】
Definition of resolution
Object
Image (erected and
same size)
Depth of Focus @5.68lp/mm
80%
70%
60%
50%
40%
30%
Focal point
(27.3mm above from
20%
scanning surface)
10%
0%
-1.00 -0.80 -0.60 -0.40 -0.20 0.00
Distance from focal point [mm]
Scan images
3mm
2mm
1mm
TM-XJ959A
(Normal) R
(Normal) G
(Normal) B
0.20
0.40
0.60
0.80
1.00
0mm
-1mm
(focal point)
【Definition of CIS output】
3. DOF : Depth of Focus
Depth of Focus indicates a change of a focus performance
on various positions of the object from focal position on a
lens-axis.
Generally, the resolution becomes lower or defocused
when the scanning position is moved away from a focal
point.
The resolution is defined as MTF (Modulation Transfer
Function) value.
The MTF value is calculated by the following formula when
scanning a reference chart having a respective width and
pitch of the white and black areas.
Vpmax. −Vpmin.
MTF =
Vpmax. + Vpmin.
•lp/inch: lp/inch explains the resolution. The resolution is
defined by reading the black and white same-width stripes.
This pair of the same-width black and white stripe is called
as "line pair" (lp), and the "lp/inch " shows how many "lp"s
are printed in 1 inch.
For example, "150 lp/inch chart" means that 150 pairs of
black and white stripes are printed in 1 inch on the chart.
And, the calculation of the resolution is 25.4 (mm) / 300
(stripes) = 84.66, which is about 85μm width strips are
printed .
× 100 (%)
24
© Mitsubishi Electric Corporation

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