Chromatic Aberrations

Albert Pedrosa
Photo mania

FORGIVE me for bringing out a science term out from the lab. Unfortunately, there’s no other way to talk about this occurrence that affects the quality of images in photography. Chromatic aberration or fringing is a failure of the lens to focus the three wavelengths on a common focal plane. The camera body has nothing to do with this limitation.

Light is actually divided into three channels; red, green and blue. These colors are the ones we see through the retina of our eyes, and these same colors are seen by our camera sensors. The three colors come in different lightwaves. Red has the longest waves followed by green, and blue has the shortest waves.

When the light enters the camera lens, the three channels go through the optics and refracts differently due to their unique individual wavelengths which then causes transverse chromatic aberration. This means that the three colors are misaligned upon hitting the sensor, creating a violet or green color on the edges of the image.

There is another type of aberration which is caused not by refraction, but through focusing. Since the three channels have different lightwaves, the camera has to choose the green channel, which happens to be more dominant, to focus on, and lets the other channel be out of focus. This results in soft edges in the image.

This is a known fact and no amount of optics can eliminate this limitation, although there are expensive lenses that are designed to reduce this aberration. However, they still cannot completely remove this effect. You may experience this aberration more often when shooting in shorter focal lengths or wide angle lens. Shooting in wider apertures can also trigger this.

Since these aberrations cannot be eliminated, there are ways to reduce the effects. One way would be to avoid high contrast scenes. Aberrations are more evident in high contrast images. Another would be to avoid shooting on the extremes of your zoom lens. It means that you shouldn’t use 24 or 70 in your 24-70 lens but rather toward the middle focal length. You can also use prime lenses since they produce lesser aberrations compared to zoom lenses.

Chromatic aberrations can also be removed in post-processing using Lightroom or Photoshop. Lately, I tried the latest Lightroom 4 and PS6, and I was amazed at how much control you can get in removing aberrations. Just go to “lens correction” under the “develop” setting in Lightroom or “filters/lens correction” in Photoshop.

Note that when using LR or PS to remove aberrations, the color saturation of the entire image also gets affected. Make sure to compare the image before and after the correction. If the image becomes desaturated, then reduce the amount of correction. In PS, you can always mask the image so only the part where the aberration exists can be corrected.

Meanwhile, “The Outpost” restobar announced their closure. They’ll be open until Sunday, September 16, 2012. Photographers are really gonna miss this place since this is the best place to practice shooting performing bands. For those who haven’t tried, feel free to document the last remaining nights.

Keep on shooting, everyone!

(photography@grp.ph / www.grp.ph)