Pentax lens selection

Tulsaghost wrote:

BUT!!! All reviews seem to say you need to stop down a lens for the best image quality. Dosen't that defeat the purpose of a fast lens?

Just asking here...

Chuck

Fast lenses are mainly used for subject separation or action shooting.

Fully open, the traditional designs are usually sharp in the center, but the corners are soft, which doesnt matter for portraits or general purpose shooting, as they will be out of focus anyway, which is the reason for the 3D effect and better subject separation when shooting with large sensors ("bokeh").

Whith these traditional lenses, when you want sharpness across the frame, for architecture or landscape for instance, or group portraits, it is better to close the aperture 1 or 2 stops, which is usually possible for still scenes, thanks to image stabilization (whether in-body or in-lens).

Sigma art lenses are designed like macro lenses for corner to corner sharpness with almost no field curvature, and most aberrations are optically corrected even at very large apertures.

Though usually big, heavy and expensive, these very bright lenses (not only Sigma, but also many recent lenses from most brands) sell very well, as they are marketed as the best in class performance, proven by web reviews.

They are quite impressive when pixel peeping.

They are very good for architecture or sports, but going big is not always welcome in real life and, when watching the images as a whole, from an artistic point of view, they dont offer the same 3D effect of more traditional designs (like the Pentax limited primes for instance).

Thus, IMO, the "art" in Sigma art lenses rather means "state of the art technical performance". But of course marketing them as "art" lenses is much more efficient, as the buyer may believe they will offer improved artistic rendering.