It’s a fact of life that all lenses are imperfect; it’s the nature of lens design and physics that dictate this rather than any design flaws inherent in the lenses themselves. Whilst professional and high end lenses minimise the imperfections they will employ a wide variety of techniques to offset these weaknesses such as lens coatings, different glass for the lenses (such as Fluorite found Canon L series glass) and even manual calibration of the lens for the most perfect image. Canon RAW offers a software solution to minimise or even completely remove many of these remaining flaws.
Before we consider ACR’s tools we must understand what flaws can affect an image. There are many ways an affected by distortion or aberration, and being aware of what you lens will do will help you minimise the issues in the first place such as using a telephoto lens for a head shot instead of a wide angle lens which will distort the face.
So what are the common distortions?
- Barrel – this is where the image bulges outwards in the middle, just like an old-fashioned wooden barrel. This is most often caused by wide-angle lenses.
- Pin cushion – this is the opposite of barrel distortion where the image is pinched inwards at the centre, it’s most commonly seen at the longer telephoto lenses at maximum zoom. The problem can be made even worse with the usage of a tele-converter.
Both of these problems are particularly noticeable when you have a subject that has straight lines such a window, a tall building, a fence or similar objects that have repeating patterns.
ACR Lens Corrections Automatic section
- Chromatic Aberration – is another imperfection that affects mostly wide-angle lenses but not exclusively is where you get colour fringing on objects. Colour fringing occurs when the colour wavelengths are not exactly mapped to the same focal plane, and is particularly noticeable in high contrast scenes. This is sometimes confused with lens flare which can produce similar results in some instances.
- Purple Fringing – is the phenomena that gets commonly confused with Chromatic Aberrations, this can also be called Blooming by some people. Unlike Chromatic Aberrations this occurs at the Micro Lens level of a sensor. Unlike C.A distortions Purple Fringing will be evident throughout the image, but like C.A. it will appear at points where there is a high level of contrast between elements of an image such as a branch against a bright sky.
- Vignetting – The odd one out, the vignette effect can be a creative enhancement to an image particularly to help the viewer’s eye to focus on a particular part of the image. A vignette is essentially darkening the corners and is the result of the lens not focussing enough light to the sensor or there is an object that’s visible at the edge of the lens such as a filer holder or using the wrong lenshood. Again wide angle lenses are particularly prone to this phenomenon.
- Keystone Distortion – Not an optical or camera defect as such, it’s a side effect of not being able to photograph an object exactly parallel. A common example of this is photographing a building close up where the foundation will appear larger than the top of the building The term comes from the shape of a keystone that’s used in arches to hold the structure together.
ACR Lens Corrections Manual section
Adobe Camera RAW works by using profiles either created by themselves or by you using the tools from their website. The Adobe profiles are created by a full frame camera and then will interpolate that profile for the crop cameras. In practice this works out pretty well for most instances.
There are two modes that are available to you, profile and manual. Profile is the auto mode, and in most cases with a good profile these is generally good enough for most images. Auto mode just gives you control over Distortion, Chromatic Aberration and Vignetting where as Manual gives you total control on how to correct the image distortions.
No related posts.