Photographers are a funny bunch. One day, they tell you that it’s not the gear that matters, it’s the photographer, so you should be able to get great photos out of that old Instamatic. In the next breath, they tell you to throw away the perfectly decent kit lens you got with your new DSLR because photos shot with it will be crap. Oh, what to believe!
What you really want is the right lens for your photography. That 18-55mm f/3.5-5.6 kit lens may be just right for you, if you primarily take photos of your family in brightly lit environments, or lug it along on vacations, where the relative light weight of the kit lens makes life easier on necks and backs. On the other hand, if you’re trying to shoot your kid playing basketball in crappy gym lighting, and get blurry messes for most pictures, maybe you do need a different lens.
Let’s try to deconstruct some of the key numbers, and understand why some lenses do better than others – and why they also might cost and weigh a whole lot more. Most of the discussion will focus on zoom lenses, but we’ll touch on primes – fixed focal length lenses – at the end. Since I’m a Nikon shooter, most of my examples will be Nikon, but the principles are the same whether you use Canon, Sony or some other DSLR brand.