In the discussion following my post “Barbie, the Bikini, and the Burqa,” a point was made about the utility of the hijab.  Hijab was conceived of as being dark, loose fitting to the point of creating hazards, and obstructing vision.  As the images from http://www.gnlusa.com/catalog/index.php above show, this is not necessarily the case. 

There even styles that would not restrict work around machines or boiling vats of oil in any significant way and others designed specifically for sport.

Woven Pant

 For more informationa about hijab, see the Wikipedia entry, which is well referenced and a good place to start.  http://en.wikipedia.org/wiki/Hijab

Niqab is the face veil that might indeed obstruct vision http://en.wikipedia.org/wiki/Niqab, but it is not universally part of Hijab, as the images above illustrate.