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Lens Corrections

Lens profiles

The perfect lens does not exist. Chromatic and geometric aberrations distort images. Software corrects them during shooting or later in post-production.

Chromatic and Geometric Aberrations

Which lens is flawless? No one. When we look at how it works, two types of problems appear: chromatic aberrations and geometric aberrations. Chromatic aberrations cause colored fringes, especially visible in the corners of the image. They are caused by the dispersion of the refracted white light and its decomposition into several colors. Geometric aberrations create a distortion of the image, most often a type of barrel (convex appearance) or pincushion (concave appearance).

Sometimes the distortion takes the form of a mustache, with a barrel distortion in the center and a pincushion distortion on the edges. Geometric aberrations are more frequent on zooms than on fixed focal lengths: barrel with the wide angle to pincushion toward the telephoto position. To these defects, add the vignetting that darkens the edges of the image, especially visible at a wide aperture.

Software Correction

The ideal is a lens without aberration or vignetting. But its price would be stratospheric. The manufacture of a lens is a compromise between the ideal and what can be effectively corrected through software image processing. The aberrations are corrected at the time of shooting or later in post-production through the modeling of optical aberrations. The programs apply specific corrections for each fixed focal length (or different focal lengths if it is a zoom), for each aperture, according to the focusing distance. They automatically remove unwanted color fringes and distortions.

During Shooting

Over the last twenty years, lens and camera manufacturers have gradually included corrections in the JPEG and Raw files. When you shoot in JPEG format, the image is automatically corrected. In Raw, it retains its aberrations, but the integrated profile makes it possible to display the corrected image. Olympus and Panasonic, in 4:3 format, include a lens correction profile with the Raw file.

Camera-Lens Profile

In post-production, most image processing software offer correction profiles for each combination of the camera and lens. DXO has been integrating corrections adapted to camera-lens pairs since 2004. Updates are regular and performance is optimized. Competitors have followed, including Adobe which integrated in 2010 an automatic optical correction in Camera Raw 6.1 and in Lightroom 3. Capture One 7 added it in 2012.

Correct With Subtlety

Automatic corrections eliminate chromatic aberrations, distortions and vignetting. The first should be systematically applied, because fringes are most often annoying, but distortions and vignetting do not necessarily degrade the image. A subject without a straight line (a portrait, for example) can remain as is. And vignetting can darken the corners of the image with success. It’s a matter of personal judgment.

Built-in Profiles and Post-production

When the cameras’ built-in profiles for the Raw format (Olympus and Panasonic in 4:3) are recognized by Lightroom and Camera Raw, Adobe does not provide a custom profile. In the lens correction panel, the “i” information warns that the built-in profile is applied. It is the same with the Fujifilm X or Leica Q Raw. This does not prevent you from exploring the possibilities of adjustment in manual mode if the built-in profile shows a little distortion. If Lightroom warns “Unable to find a matching profile automatically” (this message is sometimes displayed), the profile is in fact applied.
DXO does not take into account the built-in profiles of the cameras. It applies its own profiles, which are better than the built-in profiles. DXO can show the uncorrected image. We then see the extreme distortions of short focal lengths in 4:3 and the inevitable cropping due to geometric rectification.

Discover the photography courses at Spéos

Spéos offers various training courses ranging from simple one-week photography courses (initiation and advanced level) to 3-year courses. The long courses to become professional photographers allow you not only to master all the photographic techniques and its vocabulary (blurs, hyperfocus, sharpness zone, depth of field, backlighting, focal length, shutter release, autofocus, wide-angle, rule of thirds, etc.), but also all the stages of shooting and image processing.

Visiting the school allows you to discover the premises, the studios and the equipment, and is undoubtedly the best way to familiarize yourself with your future way of working. This is why, in addition to the open days, Spéos offers throughout the year personalized visits by appointment to come and discover the school with a member of the team.

Without a correction profile, the image can show a very pronounced distortion, especially with wide-angle lenses. With a proper profile, the lines are square. DXO profile from DXO PhotoLab 6. Olympus EM5, 12 mm f/2 lens.

1/ Lightroom Profile
Lightroom has correction profiles for most of the lenses available on the market from camera makers (notably Canon, Nikon or Sony) to independent manufacturers. They are made by Adobe. Here, the profile of the Nikon24-70 mm f/2.8 lens for the Nikon D850.
2/ Built-in Lightroom Profile
Lightroom uses the correction profile embedded in the Raw file for 4:3, Olympus and Panasonic lenses. A message indicates “Built-in lens profile applied”.
3/ DXO Without Custom Profile
If Lightroom automatically integrates the built-in profile to the raw file, DXO PhotoLab proposes versions with and without correction. In manual mode, the operator can adjust barrel, pincushion or fisheye distortions. But not the mustache shape.
4/ DXO With Custom Profile
In the automatic version based on the DXO optical module, PhotoLab uses a specific profile based on the camera body + lens combination. The correction is instantaneous and overcomes irregular distortions. The lines of the subject find their original straightness.
5/ Grid Check
The image processing software has a grid to check the straightness of the lines. In the Lightroom development module, select View > Loupe Overlay > Grid. The Ctrl (PC) or Cmd (Mac) key controls the size and opacity of the grid.
6/ Manual Adjustment
The integrated profile or the profile of the post-production software, as here in Lightroom, can be adjusted manually. If distortion remains despite the automatic correction, the barrel or pincushion distortion remains adjustable.

Text and photos: Philippe Bachelier, teacher of Printing techniques at Spéos

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