Advantages of a Zoom
Versatility
The most obvious advantage of a zoom lens is its versatility. Depending on which zoom you have, you’d be able to go from wide-angle to telephoto in a quick turn of the zoom ring. Being able to throw one lens on your camera body, and to then be able to use just that one lens for a handful of different compositions and situations is easier.
Size, Weight, and Portability
Having one zoom lens take the place of potentially several primes can be advantageous as a single lens obviously takes up less space in your pack than several. The size difference between a 600mm prime and a 150-600mm zoom is significant, as is the weight between them.
Disadvantages of Zoom
Quality
Again, the overall image quality of zoom lenses is definitely getting better all the time. But, its not there, yet. The zoom lenses are simply not going to be as sharp as a like-prime lens.
Zooms are less sharp because of optical errors coming from their complex nature. Expensive unique glass elements and coatings correct some of these errors. As a result, you’ll see a drastic increase in quality.
Choosing a zoom over a prime telephoto using reasons provided within this, or other, articles, is a compromise. If the number one problem you’re faced with is weight and packability, you may decide that the zoom lens is “good enough,” and go with it. If you know that prime is going to be your best option to get your best images possible and that in your mind is clearly number one, there you have it.
And, don’t forget, an expensive zoom will easily surpass a cheap prime, so make sure you’re comparing apples to apples.
Speed
For some of the more pro-level zoom lenses, speed is not a huge issue. My 24-70mm f/2.8 is quite fast. Fast enough for most of the situations in which I use it for. However, the f/1.8 of the 600mm prime used for wildlife is nice, to say the least. When compared to, say, the 150-600mm zoom from Tamron, where the aperture will vary between f/5-f/6.3, this is a large advantage for the prime.
Conclusion
This article was certainly not designed to make an argument one way or the other regarding prime vs. zoom lens choices. Perhaps you use both zoom and prime lenses, as I do. A lot of serious photographers will have a lens setup that includes a “nifty 50” prime, a collection of zoom lenses covering the focal spectrum, and then, perhaps, that one big telephoto prime.
It can’t be overlooked, however, that owning a telephoto prime is certainly dependent a great deal on how much money you can spend on camera gear, and how often you’ll use it. Taking time to consider which gear suits your shooting style best is certainly worthwhile and as long as you are having fun making images you are proud of, what really is the difference?