Rienzphotoz said:
A lens hood cannot stop dust, dirt, grime, oil, grease, finger prints, water etc falling on the lens front element
Actually, a lens hood is superlative at stopping most of those things. Better than a filter, in fact.
Take fingerprints, the most common. Fingerprints obviously happen when your finger comes in contact with the front lens element. When the front lens element is the forwardmost part of the camera, it's quite natural to touch it in all sorts of circumstances. But, with a hood, you've now got to actively stick your finger past the hood and reach in to touch the front element. Short of curling your fingers around the hood or pointing and sticking your finger straight down the front, there's no way to get a fingerprint on a hooded lens.
Basically, without a hood, touching the front of the lens is almost natural. But, with a hood, it takes active intent or extreme carelessness on the part of the photographer to touch the front element.
Now, let's examine the next most common situation: water droplets in rain. Unless it's a driving rain in a strong wind, or unless the camera is pointed up, no rain is going to fall on a hooded lens.
Oil and grease are both only going to happen from physical contact, which the hood will prevent even better than it'll prevent fingerprints. Casually walk around an auto mechanic's shop letting your camera bang into every oily, greasy, grimy surface, and, if you've got a hood on, you'll have to actively aim the camera in order to get anything to touch the lens.
That basically leaves fine blowing dust and water spray from waves or the like, both of which are textbook cases for where filters are not only a good idea but required in a small handful of lenses to complete the weather sealing. But few photographers do much shooting in those kinds of environments...which takes me back to my original statement that most photographers most of the time don't need a filter to protect the lens, but all photographers concerned about protecting the lens should be using a hood.
Basically, unless you shoot in certain unusual situations, if you use a hood, the only thing you'll ever have to do to clean your lens is use a rocket blower once in a blue moon, and maybe supplement that with a soft brush. Leave off the hood, and prepare yourself to get on good terms with lens pens, pec pads, and Eclipse -- whether or not you use a filter.
If nothing else, look at the hood as the best way to protect your $150 filter from fingerprints and scratches and what-not.
Cheers,
b&