i c. Mine lens hood came together with my 18-20mm VR lens. So will it suffice?
Don't get too carried away with too many hearsay or gadgets when you already have what came with your lens. Some of what some folks here wrote is subjective and some I think was more in jest.
If your lens comes with one...good to use it NOT WASTE money to change to some 3rd party hood thinking it will improve your skill and shots!
If you have no idea as to why you need and NOT need a hood...best to stick with what you have. In these day and age most lens like zooms already comes with one and it WORKS. Why I say this is because the hood you got with your lens is specially MEASURED to not just fit the diameter of your lens front...but more importantly...it will not block or cause darken corners in the pictures you shoot. You get darken corners in your picture due to having a hood that cover a tighter focal angle then the angle of your lens!
Example...your 18-200mm zoom, you went and buy a 3rd party hood. Unknown to you ..that hood is meant for use on lens of say 24mm onwards 200mm or beyond. The problem is this....when you zoom out to shoot at 18mm with that hood on your lens, you will have impaired the full view your 18mm focus length and thus create some dark corners in your shot. This is the same problem when some people stack more then one filter to their lens. And usually this is a big problem with wide to super wide lens.
So if you already have a hood that come with your lens...stick to it...it was probably specially measured and built for it and to work with all the focus lenghts that makes up that particular zoom. The only time you might buy a hood would be if you use prime lens that share the same mouting thread and you are aware of all the hood focal angle sizes and not mistakenly use one that is too small for that focal lenght. Hope you know what I mean.
It does reduce lens flare but then again...these days most modern lens has special coating on the glass element that will help reduce flare too. Stray light from the sides of the lens can effect a shot and thus that hood will help but to always help improve constrast that is not true in general. It protects the lens in a way when you walk about and have your camera sling to your neck and the front of the lens ( especially long lens) knocks against people or pillar...etc. In some way if you drop your lens....hopefully it hit the ground and the hood takes the knock first..heheh but then again...will it save your lens..that is hard to say lah. So if you already have your hood that comes with your lens...be happy with it and don't get into that buying this and that thingy. I nfact if you are new to photography..stop buying other stuff and take the time to learn about the basis and what your camera and lens can do. Most modern camera and lens are alot better equipped to deal with some of the "old" problem that older SLRs faced before.
That is just my view...