Optical Zoom Lenses
A camcorder with an optical zoom lens has the ability to magnify faraway objects. It does so by moving pieces of glass within the camcorder. Optical zoom lenses are distinguished by how much magnification they offer, so a 10x zoom lens can magnify an object ten times.
Fixed Focus Lenses
A fixed focus lens is one that does not move to achieve magnification. It is "fixed" in place. Many camcorders with a fixed focus lens will nonetheless offer a "digital zoom." Unlike its optical counterpart, a digital zoom doesn't really magnify a faraway object. It simply crops the scene to "focus" down on one particular subject. To learn more about how a digital zoom operates and why it's different (and inferior) to an optical zoom, click here.
Understanding Focal Lengths
The focal length of a lens refers to the distance from the center of the lens to the point on the image sensor where the image is in focus. Why does this matter? Well, the focal length is a more complicated way of telling you how much zoom your camcorder offers and what angles it captures.
Focal lengths are measured in millimeters. For camcorders with optical zoom lenses, you'll see a pair of numbers: the first giving you the focal length at the wide-angle and the second giving you the maximum focal length at telephoto (i.e. when you've "zoomed out" or magnified a subject). If you like math, you can determine the magnification, or "x" factor of your camcorder by dividing the second number in the focal length by the first. So a camcorder with a 35mm-350mm lens would have a 10x optical zoom.
Wide Angle Lenses
A growing number of camcorders have begun to tout wide angle lenses. There's no hard and fast rule for when a built-in camcorder lens is considered wide-angle, but you'll typically see a model advertised as such if has a focal length below 39mm. Like the name implies, a wide angle lens can capture more of a scene without the shooter having to take a step or two back to take it all in. It's a real benefit.
A lens regulates the amount of light passing through to the sensor using a diaphragm, also called the iris. Think of a pupil widening to let in more light or constricting to let in less light and you'll get an idea of how the iris functions.
The size of the iris opening is called the the aperture. More sophisticated cameras will let you control the size of the aperture. This is important for two reasons:
1. A wide aperture lets in more light, brightening your scene and improving performance in dimly lit scenes. Conversely, a small aperture lets in less light.
2. Adjusting the lens aperture allows you to adjust depth of field, or how much of a scene is in focus. A wide aperture will make objects in front of you well focused but the background blurry. A small aperture will make everything in focus.
Camcorder makers usually advertise the maximum aperture - i.e. how wide the iris can open to admit light. The wider, the better.
How Can You Tell What Your Camcorder's Aperture Is?
A camcorder's aperture is measured in "f-stops." Like the optical zoom rating, you can do some math to determine the maximum aperture of your camcorder. Simply divide the total focal length by the diameter of the lens (this is typically etched into the bottom of the lens barrel). So, if you had a 220mm lens with a diameter of 55mm, you'd have a maximum aperture of f/4.
The lower the f-stop number, the wider the lens' aperture. So unlike with an optical zoom, where you're looking for a high number, you want a camcorder with a low aperture, or f-stop number.