by Alison Perry

Rock Cairn along the Hudson is an image of tranquility by way of atmospheric space. It evokes a mood about nature, geologic time and things that remain behind. Walking along the Hudson in Piermont one evening last spring, I noticed a small pile of rocks. It looked to be a marker of sorts. The scene suggested a parallel between the rock pile and the rocky Palisades Cliffs off in the distance so I attached a wide angle lens to my camera and knelt down to photograph it. Doing so brought the two geologic elements a bit closer to each other and raised the horizon line above midpoint, resulting in a uniformly divided composition that applies the rule of thirds. The new marsh grass shoots surrounding the cairn would overtake it in another week or two but right now they were the perfect height and complementary color opposite the cool tone lavender sky and leaden waters. Offshore another set of remains protruded above the surface of the water. They were decaying dock pilings, part of an embarkation station once used to board military personnel onto naval ships bound for Europe, North Africa and WWII. The view is looking south toward NYC at twilight and was photographed from the long narrow peninsula once known as the Erie Railroad Pier.

I hadn’t shown Rock Cairn previously because it had a technical issue that bothered me, but recently realized the problem might be useful to readers. Someone once told me to pay attention to the lenses I choose since they’re more important than those really sleek and sexy black camera bodies’€¦ to which I reply’€¦ I agree! Give me great lens optics with built in sharpness and speed but with as little or no barrel distortion or chromatic aberration as possible. Thank you!

Chromatic aberration became apparent in this image during post processing. Initially, I didn’t know what it was, or that there are two types, longitudinal and lateral, but I could see both effects when I used the lens under certain lighting conditions. Through research I found it is the by-product of optically inferior lenses and that both aberration types can exist in one lens. My particular lens was a Canon wide angle zoom. I also learned the problem used to occur on acetate film and that stopping down the lens helps to eliminate the problem longitudinally, but lateral aberration can only be eradicated with post processing software. After spending too much time alleviating the problem in post processing I made the decision to purchase a better lens.

Wikipedia Commons/Chromatic Aberration

A picture from Wikipedia Commons uploaded here demonstrates an extreme example of chromatic aberration. It occurs when the different color wavelengths are not calibrated to accurately match the dispersion characteristics of the lens optics. The lens then fails to focus all colors to the same point of convergence longitudinally and/or laterally.

Longitudinal aberration occurs when the varying color wavelengths line up along the same axis within the lens, but don’t meet at the same focal point’€¦ more like in front of or behind one another. This type causes loss of overall image sharpness, which is very noticeable throughout the example, bottom right. Lateral aberration causes ‘€œcolor fringing.’€ Color wavelengths line up along the same optical plane, but don’t meet at the same axis point’€¦ more like side by side. If a lens has lateral aberration it will become very noticeable with certain subject matter and under certain lighting conditions, especially in steep angled morning and late afternoon light. In the Wikipedia example a bright cyan blue line manifests itself along the top right side of the building.

Professional camera lenses are generally more expensive than standard consumer lenses. If quality is important, purchase a better lens, the faster the better. The Canon wide angle I was using came as a package deal and at the time I wasn’t shooting professionally. Photographing landscapes with a lens that has either or both types of chromatic aberration will require a tripod for long shutter exposures and small lens openings or F-stop apertures. This will help eliminate longitudinal chromatic aberration while insuring sharpness through an increased depth of field. You’ll still have post processing work to do if your lens also has lateral aberration, but not as much.

See also:

• Postcard From New York on NyackNewsAndViews
• Chromatic Aberration: ToothWalker.org
• Camp Shanks: HvMag.com
• Chromatic Aberration: Wikipedia.org
• Palisades Cliffs: 3dParks.wr.usgs.gov

Alison Perry owns a Nyack-based photography business that combines architecture, landscape and formal space and strives to make personal art about time and place. Imagery is for sale through her website. She received BFA in Studio Art from SUNY Purchase and a graduate degree in Library Science from Long Island University. Previously, she worked in journalistic and editorial photography for several different national/regional newspapers in NYC, PA and CA. See examples of her work at AlisonPerryArt.com