What You Should Know About Optical Defects Of An Image
What are chromatic aberrations, distortion and vignetting? They all represent optical defects of an image. In our article we will tell you about the reasons, why they occur in the picture and what can be done to bring down (if needed) these defects during image editing.
Chromatic aberrations
Chromatic
aberrations are caused by the light dispersion (a process of the light
beam breakup for the compound parts), coming through the camera lens.
The matter is that light beams with different wavelength (being of
different color) are refracted under different angles, that is why, for
example, a rainbow is created from the white light beam.
Chromatic
aberrations lead to the decrease of image clearness and appearance of
color contours (especially on contrasting objects).
Distortion
Distortion
is a geometrical aberration of the straight lines. There are two types
of distortion - pincushion distortion (when the straight lines
become incurved) and barrel distortion (when the straight lines
become bulged). Distortion effect can be reached using zoom lenses at their utmost values.
Vignetting
Vignetting
is an optical effect of brightness decrease of an image from the
center to its edges. As a rule, there is no darkening in the center,
while it is clearly seen close to the edges.
Vignetting is caused by
certain lens peculiarities, which cut off the light beam, diverging
from the lens axis a lot. Therefore, vignetting is highly
visible if you use a wide-angle lens. Also its effect can be found in the lenses with the high lens aperture at maximum diaphragm.
And, of course, you may already know it, that vignetting is used as a nice artistic element of image editing.
Back Focus and Front Focus
Sometimes, when you focus on the object, you receive a picture, when sharpness is shifted to
the side of the camera - we call it front focus. And vice versa,
when focusing is shifted to the opposite side of the camera - this is
called back focus.
Generally, the lens is sending all of the light beams on one surface only, where the matrix is placed.
But if due to some reason the lens is slightly shifted - we receive an
image as mentioned above. We can solve these focusing drawbacks during
the adjustment process, which is likely to be held in the service
center.
back focus
Optical Defects Correction
Initially all of the defects are connected with the class of optics. In the low-cost lenses optic defects are more likely to be found, comparing with the top class lenses.
But in this or that case all of the above-mentioned drawbacks can be cleared with the help of the software.
If you work with RAW format you can change Lens
Vignetting and Chromatic Aberration in Lightroom or Adobe Camera
Raw in the section of Lens Correction. There are no such settings in
Capture One due to software specific character.
If you work with JPEG format in Photoshop, then go to Filter -> Distort -> Lens Correction. Here
you can change all of the three parameters: Remove Distortion, Vignette
and Chromatic Aberration. The one tip is to open your image always in 100%
scale in order to change the Chromatic Aberration option. You are welcome to discuss this article on our forum!
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