Other Measurements
EFL
EFL or "Effective focal lenght" is a key parameter
for any lens. PixleScope-OpticStudio permits measurement
of EFL with a few clicks of the mouse. |
BFL/FFL
BFL or "Back focal length" is the distance from
the last surface of a lens to the focal plane.
FFL or "Flange focal length" is the distance
from some mechanical mounting surface to the image plane.
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Magnification
When testing a lens at finite conjugates, it is more convenient
to measure the magnification than to measure the focal
length. |
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Astigmatism
"Astigmatism" means that vertical features
(tall skinny features) focus to one plane, and horizontal
features (wide short features) focus to a different
plane. |
Axial
color
"Axial color" means that
some there is not a single focal plane for all colors. |
Lateral
color
"Lateral color" means that
the magnification for all colors is not the same. Off-axis
featurs with high contrast will have a yellow halo on
one side, and blue on the other side. |
Distortion
"Distortion" means that lateral magnification
is not constant at different field angles. Photographers
may be familiar with "barrel distortion" in
very wide angle lenses: A photo of a rectilinear grid
is compressed at the edges, suggesting the shape of a
bulging barrel. |
Field
curvature
In most cases we would like the image plane to be flat,
to match the detectror (film, CCD, etc). Alas, not all
lenses have a perfectly flat field. |
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