White line on horizon

Question

I have a Sony Alpha a200 camera. Often times when I use the color fetue to desaturate blue in order to darken the sky a white line apears at the horizon or agaist another object that intersects the sky. Does anyone know why or how to fix it? Is this a Camera thing or a lightroom thing? I'm thinking that it may be possible that the line is already there but just not visible until the sky is darkened.

Answer 1

CA correction is applied with increasing intensity from image center being zero to the corner being the fulll amount. The best way to adjust CA is to select an image that has very visible CA area near the corner of an image. Usually only one slider is required, but some lenses benefit from adjusting the 2nd slider slightly. For some camera types (point & shoot) or heavy contrast situations (leaves of a tree with bright sky behind) using one of the 'Defringe' settings will clean up this sensor spill-over that the sliders don't fix.  Defringe may decrease some edge sharpness, so check your results. Recheck your image after setting the CA sliders closer to the image center (1/2 out toward corner) to make sure the correction is uniform.....it usually is but not always. Adjust accordingly.
Create a 'Develop' >' New Preset' for this lens selecting only 'Lens Corrections,' which you can apply manually on import, or set as part of your camera default setting by selecting 'Set Default Settings.' When doing the latter makes sure all of your other develop settings are at default, and not previously adjusted to some other setting.