I used to buy into the argument that sharpness is most important because it's the variable that can't be fixed in post; but years of experience trying to fix low contrast, flat color images in post has taught me otherwise. Since nowadays most lenses are plenty sharp; and since most people can't distinguish, in terms practical output, between a sharp lens and a very sharp lens; since, in short, greater sharpness rarely guarantees that actual images, in the manner in which they are viewed, will look significantly better: for these reasons I have come to regard concerns about sharpness and resolution as being, more often than not, grossly exaggerated. For many types of photography, for many focal ranges, sharpness is not as important as far too many photography enthusiasts make it out to be. (The one major exception to this is photography involving long focal lengths. In such photography, resolution may be more important because (1) many cheaper telephoto lenses aren't in fact "plenty" sharp; and (2) big cropping may be necessary at longer focal lengths for the simple reason that the photographer might not have a lens long enough to properly capture his subject.)
In terms of visual impact, I have found that microcontrast is the most important factor in determing the quality of printed images on visual perception. Microcontrast can be mimiced in PP up to a point (e.g., the clarity slider in Lightroom, adept use of curves, etc.), but only up to a point. A little bit of PP can often improve an image; cranking up contrast, clarity slider, saturation more often than not produces an over-processed mess. A lens with better microcontrast produces a higher quality raw file: and if you start out with a higher quality file, all things being equal, you'll end up with better overall output, particularly in prints. Mike Johnston, who introduced the term
bokeh into the English language,
explains the relation between resolution, contrast, and MTF charts as follows:
Quote: Technically speaking, MTF measures both contrast and resolution more or less simultaneously. In a photographer's reading of an MTF chart, however, generally the position of the topmost lines (typically 10 lp/mm, sometimes 5) will have the highest correlation to visible lens contrast. The lowest set of lines (30 or 40 lp/mm) will correspond best to actual resolving power. Personally, I pretty much ignore the lowest set or sets of lines when reading an MTF chart.
Johnston ignores the lowest set of lines because "resolution of very fine structures seldom helps pictorial photographs much, and, in my opinion, is an overrated property where lens quality is concerned."
Another important element of lens performance, perhaps the most under-rated, is color rendition. While you can make dramatic changes to color in post, making subtle changes that lead to more aesthetic pleasing results is much more difficult. Higher end lenses like the Pentax limiteds are specially designed to produce aesthetically pleasing colors in the camera. They capture subtleties of tone and hue that can rarely be matched in post. You'll never quite match the colors produced by a DA limited or DA* lens with a lens like the DA 18-55, because the raw files from the DA 18-55 don't record the same level of color information.
Post #18 by normhead
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