Canon provides diffraction correction in it's RAW processor Digital Picture Professional when certain lenses or teleconverters are used for which Canon provides full correction profiles.
Imho that approach is excellent and produces impressive results especially for some older (supported) lenses.
https://hk.canon/en/support/8202900400
https://www.dpreview.com/forums/thread/4203324
Some marketing stuff from a retired Canon website (
https://web.archive.org/web/20180225022433/http://web.canon.jp/imaging/dlo/effect/index.html):
Principle of the Digital Lens Optimizer
After passing the lens and various filters, the light has diverted from the ideal condition as it reaches the image sensor where the image will be formed. This is due to the influence of factors such as aberrations, diffraction, and the low-pass filter. If these influences can be compensated for using highly precise and specific data, the result ideally would be the original and optimal image. This is the unique principle behind the Digital Lens Optimizer. Factors contributing to optical image deterioration as the light passes through the lenses and filters in the camera were identified and converted into mathematical functions (optical transfer functions (OTF)). By applying the inverse functions to the captured image, the state of the light (image quality) can be returned to approach the state that the incident light had before entering the camera.
The factors such as aberrations, diffraction, and low-pass filter influence differ for different lenses and cameras, and they also are dependent on shooting parameters. The Digital Lens Optimizer therefore uses inverse functions that are carefully optimized and based on precise data. This makes it possible to compensate even for complex and asymmetric aberrations such as coma.
Main optical factors in image deterioration By reverting light as close as possible to how it was before entering the system by converting light transmission coefficients into functions/filters which are applied to apply to the image received by the sensor
Reduction of lens aberration
Conventional shooting practice
In photographic circles, there is a long-held rule of thumb that you should stop down slightly from maximum aperture when taking photos with a shallow depth of field for a blurry effect, or for scenes requiring a fast shutter speed. This is done to prevent a degradation of resolution in the focal area. The technique does not represent the optimal intention of the photographer, rather it is a compromise based on experience.
Produce images that are at least close to the original intention by accepting a tradeoff between photographic expression and image quality. This is a technique that is commonly used by experienced photographers.
Shooting practice with Digital Lens Optimizer
The rule about avoiding maximum aperture no longer applies when Digital Lens Optimizer is used. Because the optical characteristics will be optimized, high image sharpness with minimal aberrations can be achieved even with maximum aperture.
Whether using a fast shutter speed to capture a special moment, or a shallow depth of field for a blurry effect, the desired aperture can be chosen freely. A wider aperture also allows lowering the ISO speed for even better image quality.
Reduction of diffraction effect
Conventional shooting practice
Using a great depth of field for pan focus is one of the standard techniques of photography. But this involves a tradeoff, because small apertures could not be used if softening of the image caused by the diffraction effect was to be avoided. Conventional wisdom therefore prescribed that for better image quality, very small apertures should be avoided.
Shooting practice with Digital Lens Optimizer
The Digital Lens Optimizer is great for improving the sharpness of images taken with higher f-stops. The photographer need not worry about diffraction when shooting various kinds of scenes. The entire range, from fully open to minimum aperture, can be used, giving free reign to creativity.
Even at middle range, where image quality is generally good, aberrations and diffraction used to reduce image quality to a certain extent. With the Digital Lens Optimizer, further improvement is possible at intermediate f-stops as well.
Improvement in exposure setting flexibility
Conventional shooting practice
When shooting in the field, shutter speeds often need to be adjusted to the target. So far, this also required taking care with f-stops. If opened too much, aberrations would show up, while small apertures tended to invite diffraction. Looking for the optimum aperture that would retain sharpness while having the effect reflected in the image was one of the techniques in the arsenal of a photographer.
The question was whether to go for image quality at the expense of expressiveness, or vice versa. Even in the very moment when face to face with the object, the seasoned photographer needed to find a balance between quality and expression.
Reduces factors contributing to lower resolution across almost the entire aperture range, improving the sharpness of images taken at any aperture
Shooting practice with Digital Lens Optimizer
Because the Digital Lens Optimizer can improve sharpness over the entire aperture range, neither aberrations at full open nor diffraction when stopped down need to be a great cause for concern. Shutter speed can be at will, regardless of aperture stop.
Measures such as using an ND filter for slow shutter speeds or increasing ISO speed for high shutter speeds will rarely be called for, resulting in enhanced flexibility and responsiveness. Aperture and shutter speed cease to be a worry, allowing one's shooting style to become more creative.