The parts of a camera lens.
Before we get bogged down too deeply in all sorts of concepts and terminology, let’s take a look at what the different parts of a lens are called:
The insides of a lens are generally nothing to worry about. You know how VCR’s used to have “no user serviceable parts inside” stickers on them? Well, that is certainly true for most – if not all – camera lenses as well. The only thing you need to know about, really, is that there are a whole load of different pieces of glass inside.
Some of them will be affixed to the inside of the lens barrel, others might be moveable. The main reasons why pieces of glass inside your lens would move is in order for your lens to be able to focus, to zoom, or to assist in the optical image stabilisation process. All of these things are covered later on in this article, so keep on readin’!
The outside of the lens has a lot of different controls and attachments. Lenses can look quite different from manufacturer to manufacturer, but this graphic has the majority of things marked. The only other major control you might find on camera lenses is a “MF/AF” switch – this switches the lens between automatic and manual focus.
Let’s start at the beginning: A camera lens is a device that contains one or more lens elements. At its most basic, these ‘elements’ are pieces of shaped glass that ‘bend’ light in various ways. Each element has a slightly different function, but they play nicely together in order to form a sharp image on the imaging chip.
A camera lens really only has one job, which is to focus light beams onto your imaging chip. As simple as that sounds, there’s a hell of a lot of science that goes into lens design. The main challenge is that you don’t just want the lens to be sharp in one place: You want your photo to be perfectly sharp across the entire width of the photograph, all the way out into the corners.
If that didn’t quite sound complicated enough, there’s the issue of zoom lenses: With a zoom lens, all of the above stays true, but the lens has to focus light beams into very exact places on the imaging sensor, whilst also offering the photographer a variation of focal lengths. The full complexity of this is well beyond the scope of this article, but rest assured that the engineers designing camera lenses are bloody clever people.
Your lens has to connect to your lens somehow – and it does so via a lens mount. There are two main types of mount: Screw fitting, and bayonet fittings. The former is used so rarely these days that it can basically be ignored: All camera manufacturers have decided to use bayonet fittings instead. The benefits are obvious: It’s much faster to change lenses, the lenses are more secure on the camera body, and using bayonet fittings makes it possible to have electrical connections between the camera body and the lens – a necessity for electronic control of aperture and automatic focus.
Current-generation Canon lenses use EF or EF-S bayonet fittings. EF lenses can be used on EF-S cameras, but not vice versa. That is because EF-S lenses are designed for smaller sensors – this has advantages (if a lens doesn’t have to illuminate a full-size sensor, there’s no point in using the extra glass required; so lenses can be smaller and lighter), but it also has disadvantages: if you trade up to a full-frame camera body later, you can only take your EF lenses across, not your EF-S ones.
Nikon’s current generation of lenses are F-mount lenses; their lenses designed for smaller sensors are known as DX lenses. They also have the 1-series lens mount, for their EVIL cameras.
Each camera manufacturer has their own lens mount (the notable exception is the Four-Thirds mount, which is backed, but not used exclusively, by several manufacturers), and they are generally not inter-exchangeable.
It is possible to buy adapters to use one manufacturer’s lenses on another manufacturer’s camera bodies. This is especially true for EVIL cameras, where the small sensor sizes makes it easier to adapt to just about any lens mount – Novoflex markets 11 different adapters for the Micro Four Thirds camera mount, for example.
Third party lens manufacturers
Although Nikon lenses generally can’t be used on Canon camera bodies and vice versa, that doesn’t mean you’re stuck buying only Canon/Nikon lenses; there are quite a few third party lens manufacturers that create lenses of varying qualities. Sigma, Tamron, Tokina and Carl Zeiss all create lenses for a multitude of cameras.
Third-party lenses aren’t necessarily ‘worse’ than lenses made by the manufacturer of your camera – a high-end Sigma zoom can often be better than a similarly priced Canon or Nikon equivalent. However, if you compare the best third-party lenses with the best ‘brand’ lenses, the big-brand lenses tend to come out a little bit better in test.
If you’re on a budget, however, it’s well worth considering a third-party manufacturer. My Sigma 70-200 f/2.8 lens is not quite as sharp as the Canon 70-200 f/2.8 equivalent, but it is two thirds of the price cheaper… If you’re on a budget