QUOTE(millenia3000 @ Jun 18 2009, 04:14 PM)
hmm... so TCs are better on primes... yea.. what i've learned so far is that zoom lenses are naturally softer than primes... so is it safe to say...
getting a prime 200mm (dunno got such lens or not) and coupling it with a 2x tc to reach 400mm is better than getting a 70-400mm lens?I would not approve of that train of thought. I mean primes and zooms each have their own usage. With a prime you do get sharper images and distortions and CA are kept to a minimum but there are times when a prime just won't be the best solution.
Taking the above scenario for example. And yes there is such thing as a 200mm prime lens. With the 200mm prime you get a 200mm angle of view only. With a TC you get a 400mm angle of view. There's no way to break away from that with a prime and I don't think zooming with your legs apply all that well to that particular focal length.
With a 70-400mm zoom, however, it gives you much more flexibility in terms of composing your photo. It's much more useful when you are in situations where you need to vary your focal lengths. Example in fashion shoots.
So choose your lenses depending on what kind of situation and the type of pictures that you take more often. It doesn't mean that if you have a whole line-up of just primes, you will get better pictures than one with a line up of zooms.