Sunday, December 26, 2010


Lens Lingo

One of the things new photographers grapple with is lens lingo.
What do all those numbers and abbreviations mean?
We’ll start with the kind of lens, or lenses, that likely came with your dSLR.
Note: Each camera maker has their own lens mount design. Nikon lenses (F-mount) cannot be directly mounted on Pentax cameras (K- mount). However, someone may make an adapter that allows such a mash up.

Two Lens Types

There are 2 lens types:

Prime lenses – prime lenses have a single focal length and don’t zoom. Well you can zoom a prime lens, but you do that with your feet by moving yourself closer or farther away from your subject. Prime lenses tend to have nice wide maximum apertures, high quality optics, and many are quite costly.
Zoom lenses – Zoom lenses have a range of focal lengths that can be selected by turning a ring on the lens, and come in 3 main quality/performance/price levels: Kit (consumer) lenses, Intermediate (prosumer) lenses, and Professional lenses. There are 2 sub-classes of zooms: variable aperture, and constant aperture.

For example, Nikon offers the:
• $250 USD - AF-S NIKKOR 55-200mm f/4-5.6G IF-ED DX VR– kit lens (variable aperture)
• $1225 USD - AF NIKKOR 80-200mm f/2.8D ED – prosumer lens (constant aperture)
• $2400 USD - AF-S NIKKOR 70-200mm f/2.8G ED VR II - professional lens (constant aperture)

Kit Lenses

The most common kit lens is the 18-55 mm f/3.5-5.6 zoom lens and we’ll use that as an example. The 18-105 mm, 55-200 mm, and 55-250 mm zooms are also common kit lenses.

There may be some letters at the front of the lens name, like Canon’s EF-S and
EF, or Nikon’s AF and AF-S.
Nikon’s main kit lens is the AF-S DX 18-55 mm f/3.5-5.6G VR and it breaks down like this:
AF – S means A uto F ocus and the lens has a S ilent Wave auto focus motor in the lens. AF without the –S, means there is no focus motor in the lens, and auto focus uses a focus motor in the camera body instead. Most of Nikon’s entry-level camera bodies do not have a focus motor in them. That helps keep them smaller and more compact. None of Canon’s dSLR cameras have an in-the-camera-body auto focus motor.
DX – means the lens projects an image circle specifically for the smaller than full size APS-C size image sensor used in Nikon and most other dSLR cameras today. Both DX and FX lenses can be used on all Nikon dSLR cameras.
18 – 55 mm – means the lens can be zoomed from a wide angle focal length of 18mm, anywhere in between and up to 55 mm. 55 mm is considered a ‘standard’ focal length.
f/3.5-5.6 – is the maximum aperture the lens can be opened to and maximum aperture is tied to the lens focal length such that at 18 mm the widest aperture available is f/3.5 (Note: Lens aperture is a fraction of the lens focal length and f/3.5 is a larger lens opening than is f/5.6). As the lens is zoomed, the lens maximum aperture automatically changes until it is f/5.6 at the 55mm focal length. In other words, you can’t use f/3.5 when the lens focal length is set to 55 mm. This type of lens is known as a ‘variable aperture’ zoom lens, because the maximum aperture varies automatically with focal length. At apertures smaller than or at f/5.6, like f/22, the aperture doesn't change when the lens is zoomed between 18 mm and 55 mm.
G – means the lens does not have a manually adjustable aperture ring.
VR – means the lens has Nikon’s ‘Vibration Reduction’ system that can compensate for camera movement during an exposure.

For a more complete listing of Nikon abbreviations visit Thom Hogan's, Making Sense of Lens Acronyms page.

Canon calls their camera movement compensation system ‘Image Stabilization’ or IS, Sigma calls it ‘Optical Stabilization’ or OS. Those are the basics and all lens makers follow essentially the same conventions and each lens maker’s web site offers definitions for their abbreviations.

Lens Focal Length Range

Lenses, primes or zooms, having focal lengths of up to 35 mm are called wide-angle lenses.
Lenses at or near the 50 mm focal length are called standard lenses.
Lenses having greater than a 55 mm focal length are called telephoto lenses.

Lets take a general look at each of the 3 main focal length ranges.

1. Wide-angle lenses generally make objects in a scene look smaller than normal, but they capture more of a scene (a wide field-of-view, or FOV) than our eye’s can take in at once. That can make for some interesting photos, but wide-angle lenses accomplish that by adding some degree of distortion. Some types of wide angle lens, like a fisheye lens, maximize the distortion. Wide-angle lenses are often used for landscape and interior photography. When used to image people, people parts closest to the camera often look larger than normal and out of proportion.
2. Standard lenses get their name because they capture a scene close to what we see with our eyes. Things look neither smaller nor larger than normal (a normal FOV).
3. Telephoto lenses magnify things in the distance, so we don’t need to be so close to photograph them. In doing so they also capture a smaller than normal FOV. As the focal length of telephoto lenses increases, it becomes increasingly more difficult to hand hold the camera/lens steady enough to make a good sharp image, so a tripod is usually used with telephoto lenses that have more than 200 mm of focal length. As focal length increases, generally so does lens cost. For example, the Nikon AF-S NIKKOR 600mm f/4G ED VR lens, has a price tag of $10,300 USD.

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