What types of front-light illumination do you know?
Direct front-lighting
with LED ring
with coaxial ilumination
Diffuse lighting
with diffusor plate
with dome ilumination
Lateral Front lighting (non vertical ilumination)
Low angle lateral lighting (Dark field imaging)
What are advantages / disadvantages of e.g. diffuse front-light illumination?
high light intensity
no shadows
best for higly reflective surfaces
How does the experimental setup for e.g. dark field illumination looks like?
Explain the working principle of back-light illumination.
The light source points in the direction of the camera and is placed behind the object. On the image you can see the shadow of the object.
The Setup that holds the object has to be transparent.
What are advantages / disadvantages of back-light illumination?
+
outer contur is highlighted
simple setup
easy to measure size
-
details on objects surface are not visible
What are aberrations?
Aberrations are imaging errors.
What types of aberrations do you know?
chromatic aberrations
lateral
axial
monochromatic aberrations
spherical aberration
coma
astigmatism
distrotion
field curvature
Explain chromatic aberration.
chromatic aberration occurs due to the different refractive index of light of different wavelengths.
Explain one monochromatic aberration, e.g. astigmatism.
asymmetric astigmatism:
occur due to an asymmetric setup (e.g. cylindrical lens, asymmetric surface)
symmetric astigmatism:
occur due to off-axis position of the object
you get a different focal length in the meridional plane and the sagittal plane
Explain one monochromatic aberration, e.g. distortion.
The Magnification depends on the off-axis distance of the image.
What methods do you know to reduce, e.g. distortion?
aperture diaphragma to limit the system to the paraxial region
symmetric setup around diaphragma
Which aberrations are corrected by distortion correction, too?
lateral chromatic aberration
Last changed8 months ago
