So you want some glass. You don’t? Wrong, yes you do. Like with the post on sound, forget your camera. Lenses are arguably the most important pieces of equipment in your arsenal and can, quite literally, last a lifetime—“Buy once, cry once” heavily applies with lenses. There are so many options out there and so many numbers/letters to learn, so let’s talk a bit about the basic differences. I strongly advise you to read my post on f-stop and aperture, as it is important to consider when purchasing lenses.
“Focal length” is the “mm” on your lens. 30-60mm is generally a “normal” look, 75mm+ is considered a “long” focal length (lenses that see far), below 30mm is generally considered a “wide” focal length (lenses that let you see a wider area around you) and may or may not be “fish-eyed” (distorted on the sides, creating sharp angles on the ends).
1) *Prime vs. Zoom: A prime lens is a lens that does not zoom. A zoom lens has an “adjustable focal length,” meaning you can zoom in and out. The advantage with good prime lenses is that they are generally more “precise” than zoom lenses as they do not have the multiple pieces of glass that a zoom needs. Primes are also usually more “accurate” and provide a nice cinematic softness while still being sharp, This does not mean zoom lenses are imprecise, though cheap ones often are (as are cheap primes). A great set of lenses includes 1-2 good zooms and a set of prime lenses (usually 3-4 of various focal lengths), though everyone has different needs.
2) Used or New: Lenses are wonderful because if they are well-built (which many are) and the owner takes good care of them (you do, right?) then they can last a very long time and be great used purchases. Many sites have a strict system for rating a lens. The biggest consideration you should have when buying a used lens is the condition of the actual glass. Does it have scratches? Cracks at all? Any fungus (this happens with old lenses)? After that, make sure the focus rings and aperture rings are listed as fully functional, otherwise you’ll have poor or no control over the lens. Anyone worth their salt selling lenses will list EXACTLY the condition it is in and will provide several photos. Return policies are always a huge plus. KEH.com is an extremely popular site with the best product grading I’ve seen thus far, though their site looks like it came straight out of the 90’s.
3) What Now? You must ask yourself 3 questions: Do I need a zoom or prime for most of my work? Do I need it to be a fast lens (read the f/stop post!)? What focal lengths will I be working at? Documentary/Broadcast shooters often need fast, precise zoom lenses. If you’re making a movie (non-documentary) you generally need sturdy, fast prime lenses. That being said, you should never restrict yourself to just primes or just zooms—virtually no one does for all their work.
Now go invest in some glass!