In-camera lens corrections

Learn about in-camera lens corrections. Discover how they adjust the images that you shoot and maximise lens performance.

Digital technology provides the ability to adjust images in-camera or on a computer after capture. One area in which this can prove useful is in correcting for shortcomings and quirks in optical performance.

When lenses are designed, optical physics dictates what is possible, along with the price point of the lens and the complexities of manufacturing. In any case, it is fundamentally impossible to make a perfect lens – so, based on its design, every lens will exhibit a greater or lesser degree of optical irregularities. Typically, these manifest themselves as vignetting, where the corners of an image are slightly darker than the centre as a result of light fall-off, and chromatic aberration or colour fringing along high-contrast edges, where the lens has been unable to focus different colours or wavelengths of light to precisely the same point.

However, every design of lens has its own characteristic quirks and flaws. By mapping the performance of each specific camera and lens at a variety of focal lengths, focus distances and apertures, it's possible to correct for these irregularities and bring the lens performance closer to perfection.

These corrections were first made available in Canon's Digital Photo Professional (DPP) software, but the increased processing power of cameras has made it possible to carry out corrections in-camera as the images are captured if you're shooting JPEGs or during RAW processing in-camera if you're shooting RAW. You simply switch each correction on in the camera's Lens aberration correction menu.

A stack of rocks piled upon one another near the sea. There is dark vignetting in the corners of the image, and slight barrel distortion.

This image, taken with a Canon EF 17-40mm f/4L USM lens at 19mm, exhibits aberrations typical of wide-angle lenses, particularly vignetting in the corners of the image and some slight barrel distortion.

The same image of a stack of rocks, with the vignetting and barrel distortion removed.

Applying Peripheral Illumination Correction and Distortion Correction in-camera or in DPP can address such problems. If you're shooting RAW, it is possible to apply stronger corrections in DPP in post-production.

Peripheral Illumination Correction

In 2008 the EOS 5D Mark II and EOS 50D introduced Peripheral Illumination Correction. This adjusts images as they are shot on the camera to correct for vignetting or corner shading, making the brightness more even across the scene.
This correction is designed to work with Canon lenses. If you're using a non-Canon lens, it can result in unwanted artefacts, in which case it's best to turn off Peripheral Illumination Correction.

Chromatic Aberration Correction

In 2012 the EOS-1D X and EOS 5D Mark III introduced Chromatic Aberration Correction to remove colour fringing and haloing around high-contrast edges. It improves the overall image quality and maximises the performance of Canon lenses.

High-contrast edges showing magenta fringing against the blue sky, and the same image with the fringing removed.

Chromatic aberration manifests itself as colour fringing or haloing along high-contrast edges (left). The Chromatic Aberration Correction function can effectively remedy this image flaw (right).

A front-on photo of a brick wall showing some barrel distortion, and the flaw then corrected.

Lens distortions can be very noticeable in shots of artificial structures with regular or geometric patterns, such as this brick wall. Even if the distortions are subtle, the eye often detects that something is not quite right, and correcting them is worthwhile.

Diffraction Correction

Diffraction is the bending of the light path as it passes through the lens. It's an issue at small apertures because a greater proportion of the light is bent (in comparison to shooting at wide apertures), resulting in reduced image sharpness. This is frustrating, because typically you'll select a small aperture in order to try to extend the depth-of-field and achieve maximum sharpness across the image, and yet perversely diffraction will be reducing sharpness. Landscape photographers often need to find a compromise between these two conflicting optical phenomena.

In 2016, the EOS-1D X Mark II introduced Diffraction Correction, which compensates for the loss of sharpness at small apertures. It also compensates for the slight reduction in resolution that can occur as a result of the presence of a low-pass filter in the sensor. The low-pass filter is important for avoiding moiré interference in images with fine repeating patterns.

A picture of a traditional church building with skyscrapers rising into the sky behind it.

When you're shooting JPEGs using a camera that offers the Digital Lens Optimizer function, the camera can make image corrections that are otherwise available only in post-processing or in-camera RAW processing.

The same picture of a church with skyscrapers behind it, with aberrations corrected using Digital Lens Optimizer.

In-camera DLO supports highly precise correction of a wide variety of aberrations, including flaws introduced not by the lens itself but by other optical factors including the camera's low-pass filter and primary colour filter.

Lens Correction data

Initially, distortion correction data was stored on the camera for some lenses, and if you wanted to use other lenses the optical correction data for those lenses had to be downloaded via the EOS Utility software and registered to the camera. However, since the introduction of the EOS 5DS and the EF 11-24mm f/4L USM lens in 2015, this data has been stored in the lens itself. This means that the camera can access the lens data and apply it when processing JPEGs in-camera. If you're shooting RAW, however, you will still need to download the appropriate lens profile on your computer.

Digital Lens Optimizer

Canon first introduced its Digital Lens Optimizer (DLO) as a function in Digital Photo Professional (DPP). It is able to correct a wide variety of aberrations including coma, astigmatism, sagittal halo, field curvature and spherical curvature, which could not normally be addressed.

The EOS-1D X Mark II featured the Digital Lens Optimizer as an in-camera post-shot editing function. However, in 2016, DLO was introduced as a shooting feature with the launch of the EOS 5D Mark IV.

In-camera, DLO applies its corrections to JPEG files. When it's activated, Chromatic Aberration and Diffraction Correction are not selectable within the main menu, but are part of the DLO corrections. It is also possible to turn off Peripheral Illumination Correction if, for example, you want the framing effect of vignetting in a portrait.

All EOS R System cameras use lens correction (and other) data that's stored in the lens. Thanks to the super-fast communication speed of the RF mount, particularly when you're using RF lenses, shooting with DLO turned on does not reduce the maximum continuous shooting rate, as it did in earlier cameras such as the EOS 5D Mark IV.

Angela Nicholson

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