how does Chromatic Aberration happen

chromatic aberration for photography

In Photography, photography-tips by Bob Wild

Who Said:
A good photograph is one that communicate a fact, touches the heart, leaves the viewer a changed person for having seen it. It is, in a word, effective.

Irving Penn

Chromatic aberration

chromatic aberration

Purple fringe

Chromatic Aberration’ (CA) –What’s the Cause and Ways to Avoid It
Many photographers that I know have little nuisances. Things that bother us when working on a project or an assignment. One of them is chromatic aberration (CA).
When shooting your photos, you need to think about several different things before you take a shot – backgrounds, lighting, composition, and the camera settings among them.
After putting in your effort and time to produce a decent photo, the last thing you want to see when you are viewing your pictures on a computer screen is some visual problem which ruins the image.
You may have heard several photographers talk about “chromatic aberration” like it is a disease. When examining their photographs carefully, nearly every photographer has come across a scenario in which a colored halo (usually red, green or purple) is visible around specific elements of a scene.
This form of visual anomaly is called chromatic aberration (more commonly known as color fringing). In this article, I’ll try to make you understand what causes this and learn ways to avoid it.
What’s Chromatic Aberration?
Chromatic aberration also referred to as color dispersion or fringing can be an issue in the most expensive lens. What be thy cause you may ask? 🙂 When light is refracted (bent) incorrectly by the lens this makes a mismatch at a fo

cal point where the colours fail to combine as they should.
To help you understand, remember that the focal plane is the point of focus of your sensor, where the total light from your lens should be detected correctly by your sensor. Based on the lens’ construction, the focal length, and aperture, specific wavelengths (colors) may arrive at the points after or before the position of the focal plane.
When this happens you will notice color fringing around the edges around subjects / objects in your image. Removal of low levels of the chromatic aberration in can be accomplished in Lightroom and Photoshop. Where is the most obvious place that CA will occur, Trees!
Why Does Chromatic Aberration Happen?
Chromatic aberration occurs because your lens acts as like a prism; bending light based on the different glass properties, and much like a triangle-shaped one made famous by Pink Floyd :-), colors that pass through it split at various angles.
Keep in mind that light consists of many different wavelengths (colours). Therefore, for the sensor of your camera to detect the combined light color, your lens should make all wavelengths of that particular ray strike the same point on your camera sensor.
It may sound simple, but you should consider the fact that different wavelengths (and therefore different colors) will be striking the lens all at once and each of these rays will behave a bit differently based on the glass which it’s passing through.
The manufacturer’s use of a lens array helps to attain the feat of engineering needed to align all of these distinct light rays correctly. In fact, if you’re to pull your lens apart, it would not be surprising if you discover upwards of 16 elements all designed to correct the light-wave along the journey of the light between your lens and your camera sensor.
Unluckily, this is also where the chromatic aberration often rears its unpleasant head. The design of these lens elements hide defects– either in the design of the lens itself or the glass – that under certain conditions may cause your images to exhibit this kind of aberration.
I am not trying to say that you should only purchase pro-level lenses, in fact, the main point to remember here is that all lenses can suffer from the chromatic aberration in one way or another. Case and point, I owned a 70-200mm 2.8 L-series Canon and on my 7D I would often incur CA. What matters is whether or not your lens displays visible chromatic aberration, and whether this is a deal-breaker or not for your case.
Avoiding Chromatic Aberration Defects
Chromatic aberration can be effectively eliminated in post-processing if you’re shooting in RAW. But, great practice states that you need to try and get rid of issues in-camera first, instead of creating more work down the line.
Check the Focal Lengths
Even though it’s nice to have access to a broad range of focal lengths, the fact is that many zoom lenses will exhibit different aberrations at the longest and shorter extremes of their focal range. Therefore, being able to select a different focal length ‘may’ assist you to get rid of the problem of visible chromatic aberration.
Similarly, using a zoom lens at a wide-angle may introduce not only chromatic aberrations but also other defects in your shot. Consider selecting a superior wide angle lens to do the job, or make a panorama at the focal length which doesn’t exhibit the chromatic aberration problem, then join the images in post-production for an excellent result.
Reframe Your Subject to the Center of the Picture
Chromatic aberrations usually happen as you move away from the center of the frame. It’s generally due to the curvature of the lenses in the barrel. So, if you can reframe your subject closer to the center, then you may reduce issues with chromatic aberration and some other lens-based defects chromatic aberrations, or even remove completely,
You may have to crop your photograph after shooting to attain the required composition this could be an issue if you must maintain each pixel in your image. On the other hand, if you’re working with digital distribution or small prints, then the differences between resolutions aren’t visible until you step down significantly.
Avoid High Contrast Scenes
Chromatic Aberrations usually flare up in high contrast situations. It may affect your landscape shots against a bright sunrise, pictures against white backdrops or shots where the source of light is behind the subject. Sometimes there is nothing you can do except try and reframe your image. Swap your backdrop out to something that matches the primary color of your subject better, or just wait for more favorable lighting conditions.
If you must capture this image as it is, then you should swap over to RAW and get ready, be prepared to do some touch-ups in the post-production.
Stop Down Your Aperture
While this will rely on the exact type of lens, you’re using, stopping down your aperture will assist you to play down the visible effects of many lens defects, including the chromatic aberrations. Keep in mind that you may have to consider boosting the ISO or dropping the shutter speed to compensate for the loss of light if working in a non-studio environment.
If you’ve access to flashes or lighting, then experiment with the effect of enhancing and adding in more light.
Hopefully, after reading this, you have a better, understanding about Chromatic Aberration, the cause and how to avoid it in camera. Yes! Remember you can always fix it in post. Keep an eye on it and hopefully, now that you know about CA you can keep it out of your prints, trust me when I say nothing spoils a good print more than seeing chromatic aberration in that 20×16 250$ photo you just pick up from the printer.

PS – now that you know about chromatic aberration, did you happen to notice the
picture at the top? 🙂 Look very closely at the roof line

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