Learning Lens Basics

You know what the best part is about having a SLR camera?  Interchangeable lenses!!!  This is a HUGE advantage over the fixed lenses that are on almost all consumer cameras.  Why?  Because lenses need to specialize in order to truly be great.  Even today, there is not a perfect "one lens solution" that can shoot every type of shot well.  However, before we can talk about different kind of lenses, we'll need to get familiar with a couple of basic concepts:

Zooms vs. Primes

There are two types of lenses, the kind that zooms in and out (zoom lenses), and the kind that don't (fixed-focal length or "prime" lenses).  If you just thought, "Why in the hell would I buy a lens that doesn't zoom?!?!" then keep reading.

Zoom lenses can be wonderful things, but they are tricky to engineer.  That can result in some compromises on sharpness, weight, cost, and other specifications.  On the other hand, primes are simpler to design and have less moving parts.  This can result in lower cost, lighter weight and often increased sharpness, although you sacrifice the ability to zoom.

Angle of View

Angle of view describes how wide an area the lens can "see" at one time.  A wide-angle lens is what nature photographers use to show sweeping landscapes.  The opposite of this is generally referred to as a "telephoto" lens (not a "narrow-angle lens" as one might expect).  The same nature photographer might use a telephoto lens to capture a tight shot of a bird in a faraway tree.  In the middle of this range are "normal" or "standard" lenses.  They are well suited for general photography and are often said to approximate the natural angle of view of the human eye.

Angle of view is specified in degrees, but you don't often see this written on camera lenses.  Instead, they give you focal length, which is a little more complicated.

Focal Length

A full definition of focal length is complicated and not that helpful (go see Wikipedia if you don't believe me).  What you need to know is, focal length affects angle of view.  The shorter the focal length, the wider the angle of view.  The longer the focal length, the narrower the angle of view.  Focal length is pretty much always given in millimeters, so a 28mm lens is much wider than a 105mm lens.

It's almost that simple.  The only complication is, angle of view is also affected by the sensor size of your camera.  I really have to use an example to explain this.  Nikon's digital SLRs have one of two sensor sizes: FX or DX.  The larger FX size is the same size as a frame of 35mm film.  The smaller DX sensors are 2/3rds that size.  As a result, a 28mm lens on the larger FX sensor gives the same angle of view as an 18mm lens on the smaller DX sensor.

To try to simplify things, 35mm film is used as the standard.  Lenses often say "equivalent to such-and-such focal length on a 35mm camera".  To keep with our Nikon example, a 18-55mm zoom lens designed for a DX camera may also say "equivalent to 28-80mm on a 35mm camera".  Not the best system, but its what we're dealing with.

Maximum Aperture

Back to something easier and more familiar!  Maximum aperture is the largest available aperture setting for a lens.  This is important because a large aperture can let in more light and therefore works better in low-light situations.  A f/1.4 maximum aperture is about the largest you'll see.  f/2.8 is the standard maximum aperture for expensive professional lenses.  f/4 to f/5.6 is typical among more affordable amateur lenses.

Minimum Focus Distance & Magnification

These are the important specs for close-up photography (flowers, etc.).  Minimum focus distance is just what it sounds like: the closest distance you can focus at.  This can be anywhere from a few inches to a few feet.

Magnification is how large the subject appears in the image compared to in real life.  A "1:1" magnification ratio is basically like you laid the object right on the image sensor.  So if your sensor is the size of a postage stamp, you could take a picture of a postage stamp and fill the entire frame with it.

Compatibility

Make sure the lens you buy is compatible with your camera!  Different brands of cameras have different types of lens mounts, so you need to make sure the lens will actually attach to your camera.  Sometimes that is only lenses with the same brand as your camera, but there are also manufacturers who make lenses for multiple different brands.  Even within a brand, some lenses are not compatible with certain cameras, or limit the features you can use (such as auto-focus, metering, etc.).  Do your research before you buy so you don't get a nasty surprise!

Vibration Reduction (VR)


This feature helps minimize vibration and reduce the dreaded "camera shake" at low shutter speeds.  Also called image stabilization (IS).

Recap

Here's an example of a lens you might see for sale online:  Nikon 18-55mm f/3.5-5.6 VR AF-S DX lens.  Confusing right?  Let's break it down:

Focal length: 18-55mm (this is a zoom)
Maximum aperture: f/3.5 - f/5.6 (this means the maximum aperture changes over the zoom range: f/3.5 zoomed all the way out, f/5.6 zoomed all the way in)
VR: Has vibration reduction.
AF-S and DX:   Two examples of compatibility specs, which differ from brand to brand.  Some Nikon cameras have to have AF-S lenses in order to auto-focus.  The DX means this lens is only designed to work on DX-sized sensors.

Up next, real talk about the types of lenses you want to buy.