Can somone help me to decide about camera lenses...details below?

I purchased a Vivitar 28-85 macro focussing lens for my son's OM camera and have the opportunity to purchase a Zuiko 35-70 f4 zoom lens for the same camera. Ignoring the difference in makes and range I wish to know as a non camera person whether these lenses basically fulfil the same function, in other words he should not need both lenses. Help!!

Since they both cover the same range of distance it is a waste to get another lens. But if possible you should get the brand name lens for that camera body for best shooting exposure. If not then Tamaron are the best alternative. Vivitar is ok, don't waste money on anything else, they literally are crap.

They are both moderate wide angle to moderate telephoto. Lenses like this are nice because you can just leave them on the camera for most shooting, you don't need a 'standard' lens. Also macro focussing can come in handy.

I would think the Vivitar would be just generally a better lens than the Zuiko.

Both lenses do about the same. The vivtar 28-85mm is a niece Portrait lenses, but I believe the Zuiko has a better quality glass. You did not say how fast the Vivitar lenses was. A F2.8 would be better than an F4. Remember the lower the number F4, F3.5, F2.8, F2, F1.8, the less light you have to have to take a Good picture without using a Flash. He DOES NOT NEED BOTH LENSES.

The zoom range of the Zuiko is completely covered by the Vivitar lens, so purchasing the Zuiko would not be justified for that reason. You do not say what the maximum aperture of the Vivitar lens is, but typically the Series 1 lenses were similar.

Vivitar did not make their own lenses (see link) while the Zuiko is made by Olympus. Both have good reputations. If the Vivitar is a Series 1 lens, these have a very good reputation.

ps - I have an extensive collection of lenses that I don't really need!! Some of them fill niche needs, such as a relatively slow 50mm true macro lens which has a conventional, but very fast compantion of the same focal length. However, for something this close in the circumstance you describe, it will be really hard to justify the purchase merely on need.

The first number in the zoom focal length is the minimum focal length, the second is the maximum. Therefore the range that is covered by the 35-50 is also covered by the 28-85 (and then some). So unless the optics of the Zuiko are better (i.e. it is a sharper lens) you probably don't need it.