On the Fringe

Deck chair left and right: White stripes have a green fringe on the inside and purple on the outside due to chromatic aberration

Another problem that almost all lenses produce is chromatic aberration. Again van Walree has one of the better explanations. Whereas radial (barrel) distortion will interfere with panorama production because the images diverge very quickly from one another – thus making it necessary to have a sharp transition from one photograph to the next or risk having highly divergent control points, chromatic aberration will interfere with the identity of control points in highly contrasting areas. Consider the transition from white to black to white on the left hand side of an image: Continue reading

Battle of the Bulge

Original. In particular, straight lines will be curved under distortion.

A common form of photographic distortion is barrel distortion and its counterpart pincushion. Straight lines such as architectural features become curved and this is distracting, not only for viewing buildings, but also in portraiture, where the barrel distortion will easily make you 5 or so kgs overweight. Photographers will compensate for this by using the zoom to reduce the amount of distortion (and this, as it turns out, is true, although not the whole story). Continue reading

Bracketing

A major drawback of digital photography, and one that I have been aware of all along, is the lack of dynamic range, the difference between how dark is going to finish up as black, and how light will result in pure white. The closer these two values are, the greater the contrast, but there will be no detail visible in light or dark sections. The eye and its brain have an extraordinary dynamic range which allows us to see details both in the very dark and the very bright at the same time. Continue reading