No lens hood, no matter how deep or well designed, will protect "the front element of the lens from direct light rays." That doesn't mean that a bright light, directly in front of the lens, will cause acute flare and image degradation. I've seen a few Pentax and Zeiss T* lenses that controlled flare in that circumstance very well, although "controlled flare" does not mean the absence of flare.
A longer hood will protect against flare from a narrower angle than a short hood. Over the years I've made numerous tests using various lenses with different length and diameter hoods and a bright light. In all instances a longer hood reduced the angle at which point flare became a concern or the bright light entered the frame and degraded the image, either through flare or by upsetting composition. Unless a photographer is willing to invest the time to do such tests, and invest the $$ for a wide variety of lens hoods, it's probably best to use the deepest hood possible. Shel > [Original Message] > From: Mark Roberts > Mike Johnston wrote a good SMP column about flare, lens hoods, etc.] > > http://www.luminous-landscape.com/columns/sm-03-01-12.shtml > > "By the way, a common misconception about lenses is that you need the > longest possible hood to protect the lens. This isn't necessarily so. > With some lenses, acutely-impinging light is the biggest cause of flare, > more so than more directly impinging light. A short lens hood which > protects the lens from this glancing sidelight will serve well to reduce > flare, even though it's relatively useless at protecting the front > element of the lens from direct light rays."
