AV News 186 - November 2011
The following simple diagrams demonstrate the extent that barrel and pincushion
distortion can be introduced to an otherwise normal image, most photographers
would generally only apply this extent for creative purposes and to achieve
special effects.
If you actually need to apply this amount of
'correction' to try and counterbalance the
aberrations of any camera lens, then that
lens should be firmly relegated to the bin.
This first image has no corrections
applied, the slider control is set to zero and
therefore it's grid pattern appears normal.
Each of the squares remain square and the
outer rectangles remain rectangular, exactly
as you would expect.
Our second image has 100% 'Barrel
Distortion' applied and now this image takes
on a dramatic and unexpected appearance,
distorted to the extent that the internal grid
pattern becomes much larger than the actual
frame, overflowing at the edges and even
removing the black outer rectangular border.
No doubt the creative potential of this effect
is already envisaged. However even with
creative effects in mind this level of distortion
should be used rather sparingly.
The third image has 100% 'Pincushion
Distortion' applied, which is the exact
opposite of Barrel Distortion. Whilst this
image is obviously very severely distorted
the effect is nowhere near as dramatic as
with 100% Barrel Distortion, although the
outer rectangular border has almost
disappeared being just about visible at the
very top and bottom centre. It's quite difficult
to believe that all these images started as
identical grid patterns with borders.
It's interesting to note that an illusion is at
work, all images are actually the same size
but don't seem to be. The last image is the
'Vignette' which has minus 100% vignette
applied, the darkening effect on corners is
quite dramatic. This effect can happen with
an inappropriate lens hood or front lens filter,
it can be 'corrected' by applying the
appropriate plus value instead of the minus
value as used here, it's very easy to correct
using the slider control. We may address the
creation process of lens profiles more fully in a future edition of AV News.
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