In the previous post I discussed the three basic categories of lenses—normal (or standard), wide angle, and telephoto—and the most common uses for each.
All lenses are described in two ways:
- Focal length (as measured in millimeters)
- Speed (maximum aperture size).
Here’s a rundown of what features to look for in a new lens, along with exactly why they matter.
The first thing a photographer learns about a lens is its focal length. Measured in millimeters, the focal length is an optical spec that indicates whether a lens will produce a wide, normal, or telephoto angle of view.
The smaller the number (e.g., 17mm), the greater the angle of view will be. The larger the number (e.g., 300mm), the more telephoto a lens will be.
The focal length of a lens is important because it gives you an idea of how its angle-of-view and perspective relate to our own vision of the world.
Aperture is the opening in a camera lens that allows light to reach the digital camera sensor. Just as the pupils in our eyes expand and contract depending on the amount of light around us, the aperture opening of a camera lens can be made wider or smaller to let in more or less light as needed.
Lens speed is described by its maximum aperture size (lens opening).
Lenses with larger maximum apertures can let in more light, allowing you to shoot in dimmer conditions without having to boost ISO.
The larger the aperture (the variable opening in the lens through which light passes), the more light can be let into the camera and, therefore, the faster the shutter speed that can be used.
Smaller ƒ-stops (like ƒ/1.4 or ƒ/2) indicate larger openings and faster lenses. These are desirable for several reasons, but especially for photographers who need to work at high shutter speeds (like wildlife photographers) and in low light (such as museum where flash is not permitted). Another reason a photographer may prefer a fast lens is to produce a very shallow depth of field (as in bird photography) because the larger the aperture, the shallower the depth of field.
Prime lenses tend to be faster than zooms because they’re optically simpler and, therefore, more easily capable of transmitting light efficiently.
Some zooms incorporate a variable maximum aperture (like ƒ/4-5.6) that changes based on the focal length selected. This creates smaller and lighter zooms that cover a broader range of focal lengths.
The faster lenses are generally in the pro lineups from the various manufacturers so they tend to have rugged construction, use larger elements, and more refined types of glass.
As a result, fast lenses usually cost more than slower models for a given focal length, and they’re usually bulkier and heavier. As a result, they’re difficult to handhold and to lug around.
Slower lenses are smaller, lighter, and much less costly than faster lenses of equal focal length.
The fast pro lenses cost a lot more than the midrange lenses.
Canon released its new line of 500mm and 600mm super telephoto top-end professional lenses in March 2012 with a list price of approximately $10,500 for the EF 500mm f/4L IS II USM, and $13,000 for the EF 600mm f/4L IS II USM.
Understanding Lens Measurements
The numbers and acronyms on a lens can be quite intimidating and confusing.
Camera manufacturers use this nomenclature to pack enough information to assist us in understand the lens’s abilities.
Let’s look at my Canon telephoto lens as an example:
Canon EF 100-400mm f/4.5–5.6L IS USM
EF — Auto Focus
100-400mm — The focal length of the lens in millimeters (since this is a zoom lens there will be two numbers, the widest angle length and the narrowest angle length)
f/4.5–5.6 — Aperture indicates the amount of light the lens lets through (lenses with larger maximum apertures are typically heavier, larger, and more expensive)
L — Canon’s specific code for their pro-grade glass
IS — Image Stabilization — the lens can help minimize camera shake
Please Note: This is the eleventh in a series of stories on Digital Photography and RVing
It pays to get the best lens you can afford.
—Frank Jay Hanes