Canon EF 20mm f/2.8 USM ..impecable como nuevo..
Activo desde 28/09/2017
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This Canon EF 20mm f/2.8 USM i Canon's only fixed autofocus ultrawide lens other than the 14mm f/2.8 L (1991-2007) and 14mm f/2.8 L II (2007-today). Canon has made this 20mm f/2.8 since 1992, so you can get a bargain on plenty of used ones, as well as buy it brand new.
This 20mm is very good optically, and has superb ergonomics for use with both 35mm and today's full-frame digital SLRs. Its mechanical quality is superior to most of Canon's lenses today, with a metal filter ring, metal hood mount and metal forebarrel.
Just like Canon's 14mm EF lenses, this is the world's only fixed autofocus ultrawide lens with instant manual-focus override. Just grab the focus ring at any time. Nikon has never made a fixed ultrawide lens that can do this!
With the new in-camera lens correction abilities of the Canon 5D Mark III, this is now a whole new lens, and an excellent performer. DxO Optics Pro also has a module for this Canon 20 USM for use with the 5D Mk III and other cameras.
A little-known feature of the Canon 20 USM is "Intelligent Field Curvature (IFC)," meaning that the surface of best subject focus is not flat, and deliberately curved to fit real ultrawide subjects. The 20/2.8 USM curves its plane of best focus so that objects away from the center are brought into better focus if they are closer to the camera, exactly as subjects do in real life.
This means that this lens doesn't test that spectacularly on flat targets (which make boring photos), but in actual use, the 20/2.8's images are much sharper since the plane of best focus is adjusted to focus on objects closer to the lens at the sides, tops and bottoms of the frame. In other words, a sweeping desert floor below you, or objects to your sides, will be in better focus than with a flat-field lens.
Think about most of your ultrawide shots: far away is in the center, and things at the sides and bottom (like the ground or walls) are closer to you. Yes, the sky might be farther away at the top, but we don't worry about focus in the sky. By adding this slight field curvature, more things look sharper in real pictures. Of course stopping down expands the depth of field so that everything is in focus.
More precisely, the surface of best focus gets closer to the camera as we get away from the center, and goes back out at the very corners. For most of my shots, this is ideal.
The 16-35mm f/2.8 L II and 17-40mm f/4 L have somewhat flatter fields throughout most of the image if you're a brick-wall photographer, while the corners of this 20mm fixed lens are still sharper than either of Canon's newest zooms.