The whole question of lens sharpness...

Started Jun 12, 2013 | Discussions thread
Alphoid
Senior MemberPosts: 2,266
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Sharpness is easy to measure
In reply to gdourado, Jun 12, 2013

Lens quality matters much more than almost anything else in equipment. Lens quality comes down to contrast, bokeh, flare resistance, distortion, and a hundred similar properties. Sharpness happens to be the easiest to stick a number on, so people obsess over it. It's by no means the most important. Contrast is more important (and also easy to measure), but somehow, reviewers don't give numbers it. Distortion is easy to measure, but matters less (and is also somewhat subjective -- there are different shapes and easy/hard-to-correct). Flare and bokeh are important, but almost completely subjective.

That said, sharpness does tend to correlate with lens quality -- nice lenses tend to be nice along multiple axes. Contrast and sharpness, in particular, are closely related in optical design, so sharp lenses tend to be contrasty as well. I've seen a small number of reasonably sharp lenses that take mediocre photos (Tamron 17-50mm f/2.8 comes to mind), as well as a small number of not-so-sharp lenses that take beautiful photos (my Minolta Beercan 70-210mm f/4 comes to mind). As a rule of thumb, however, most of my best lenses also tend to be my sharpest, so it is a good proxy.

The same thing happened with sensor megapixels for many years, and now with high ISO performance. They aren't the most important properties of cameras, but they tended to correlate with camera quality, so they were good things to shop on. At some point, manufacturers realized that this was happening, and started optimizing first entirely for megapixels, and now increasingly for high ISO, sometimes sacrificing more important properties in the process, so they stopped acting as good proxies.

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