Resolution And Field Of View - XIIMUS 1024CTI User Manual

The effect of MTF is application dependent. If very small details are to be examined or fine
colour separation to be performed by the image processing system, MTF might play an
important role in the application.
If the objective has field curvature, it will show up in the MTF plot as MTF dropping away from
the centre of the image. Observing the plots, it is evident that this is true to wider apertures
that have a small depth of field. This does not necessarily mean that sharpness is worse at
the edges. It can just as well be that optimal focus for objects close to the edge is closer or
further away from the lens. Normal camera lenses are usually used to photograph three-
dimensional objects and do not exhibit a perfectly flat focal field. Enlarging or repro optics
have a planar focal field and are used to reproduce flat objects.
7.2.2

Resolution and field of view

Resolution is primarily affected by sensor dimensions and the quality of optics. It is the ability
of an optical system to produce finer details at a tolerable contrast. Normally, according to the
Nyquist sampling theorem, it is required that a detail spans at least two pixels to be able to be
identified with a reasonable accuracy by an image processing software.
Because of the CCD, the fastest transition from black to white can occur within one pixel.
When using large apertures, large field of view and the 2K sensor and depending on the
quality of the objective used, image quality can be reduced at the edges due to optical
limitations. All TVI XIIMUS cameras have been designed and made to be used with standard
commercial objectives at mid-range apertures.
The focal length of optics required for imaging can be calculated from the following formula:
d L
x
F = ------------ , where
FOV
F = focal length of the lens (mm)
d = distance to object (mm)
L = length of the CCD
FOV = field of view; object size (mm)
Example 1 : The distance to the object to be imaged is 900 mm, the width of area to be
imaged is 500 mm. When using 1024 pixel 10 µm sensor the focal length of the objective
from the equation will be ~18.4, so a 20 mm objective would be ok, if the camera is moved
backward to a distance of 977 mm.
Example 2 : The size of an object within the image needs to be calculated in pixels. This can
be accomplished by rearranging the equation to yield L = FOV x F / d. Thus a 10 mm object
with a 50 mm objective at a distance of 900 mm will be projected as 0.56 mm. which equals
~56 pixels in the image (each pixel on the CCD is 0.01 mm by 0.01 mm).
© TVI Vision, 18 October 2006
XIIMUS R-GB-IR CL User Manual.
7.17 mm for 512 pixels (14 µm)
10.24 mm for 1024 pixels (10 µm)
14.34 mm for 1024 pixels (14 µm)
20.48 mm for 2048 pixels (10 µm)
Version 1.2
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