Thanks pdxflint and Otter for the detailed analysis. This is the kind of comments that I appreciate, an examination of an image and nit picking at areas that may not look so natural. I did sharpen and straighten the image in post processing. I must admit that my tripod wasn't exactly big and sturdy. I am interested in your comments pdxflint re expensive equipment. Do you think that the 5D would handle these issues in a better way??? I read all about the camera body not being important and just spending money on the glass. Confused !!! How important is the body for landscape pictures ???
It doesn't have anything to do with the camera body. Chromatic aberration, or other color fringing at areas of high contrast are usually caused by the paths of the different wavelengths of light (different colors) not converging at the same spot on the sensor perfectly - that's about as simple as I can get. It's the way the path of the light is concentrated and how stable it is, the factors which determine color accuracy and image brilliance, as well as sharpness and contrast. The "fix" for this is the use of low dispersion elements in the lens (at least one) which are made from special glass materials which reduce the tendency for glass to disperse or separate light rays into the colors of the rainbow. Different lens manufacturers call this type of element by various names; Low-Dispersion (LD) by Tamron, Extra-Low Dispersion (ED) by Nikon, Ultra-Low-Dispersion (UD) by Canon, Special Low-Dispersion (SLD) by Sigma and Super-Low-Dispersion (SD) by Tokina.
Generally, the less expensive lenses like kit zoom lenses are more susceptible to chromatic aberration, which can be seen on blowing up the picture and examining the details like bare tree branches against a white sky, where you'll often see purple fringing. More expensive glass is just better, and tend to have less of that.
The other thing with lenses used on digital SLRs is the tendencies toward spherical aberration (pincushioning, barrel distortion, light fall-off and softness near the edges.) Since the photo sensor in the camera is perfectly flat, and also reflective, this can cause specular reflection, which causes more flare and ghosting compared to the film surface in film SLRs. Also, light coming from an oblique angle out of the back of the lens causes problems with light fall-off in the corners because of the difficulty the pixel "buckets" have of capturing those oblique rays of light - result... vignetting. The "fix" for this phenomenon is the use of aspherical elements in the lens (one or more) to "straighten" out the light path before it hits the sensor.
These are generic issues with lenses used on dSLRs, and have largely been addressed by all the lens manufacturers, but clearly the better, more expensive lenses do a better job overcoming these design obstacles.
I noticed your photo was at 18mm focal length, you shot a Canon, so I'm going to assume it was the kit lens (18-55mm zoom.) That lens is not the best performer, meaning it will show some chromatic aberration (CA) issues in demanding shots, and the wider angle you use the tougher it gets to keep it in check. Some software programs can do post processing and remove some of the color fringing, but better glass gives you a better image to begin with. Of course, good glass ain't cheap...
That's why I still love my Nikkor 18-55 kit lens, and will keep on using it.
