Lens features and what to look for
There’s a lot of jargon associated with lenses, much of it from lens makers trying to distinguish their own lenses and optical technologies from other people’s, so let’s dissect it all to figure out what it all means and what you need to know.
You can check out this separate article on lens types to figure out the kinds of lenses you might want to get. This article concentrates on the features, jargon and key selling points. It’s a bit long because there’s a lot to cover, but every section has been kept as brief as possible.
Lens format/coverage
Different lenses are designed for different sensor sizes. Every lens creates an ‘image circle’, and this has to cover the full sensor area. Lenses designed for full frame cameras can typically be used on smaller format cameras too – the sensor area falls well within the lens’s image circle. But you can also get lenses specifically designed for smaller sensors such as APS-C or Micro Four Thirds. The image circle is smaller so they can’t be used on larger-sensor cameras (at least not without cropping the sensor area), but it does mean the lenses can be much smaller and lighter, and less expensive too.
Helpfully, Nikon will indicate smaller format APS-C lenses by including ‘DX’ in the name, while Canon includes ‘RF-S’ in the lens name where the lens is designed solely for Canon’s APS-C format mirrorless cameras.
Lens mount
Every camera brand has its own bespoke lens mount. Lenses made by that camera maker will (usually) only fit its own cameras. There are exceptions – OM System and Panasonic make Micro Four Thirds lenses which will fit each others’ cameras, while Sigma, Leica and Panasonic are part of the L-mount alliance, which uses the same lens mount and lenses from any of these makers.
Third-party lens makes like Sigma, Tamron, Laowa and others may make the same lens in a number of different lens mounts, but you have to be sure to specify which you want when you buy, and their may be feature differences with different lens mount versions.
Focal length/zoom range
This tells you whether the lens is a prime lens (a fixed focal length) or a zoom and, if it’s a zoom, the zoom ‘range’. The zoom range is expressed as a factor, so that a 3x zoom offers three times the magnification at its longest focal length compared to its shortest.
The focal length is quoted in millimetres (mm). It’s not ideal because the actual angle of view of a lens (its magnification) also depends on the sensor size, so with a smaller sensor, the angle of view of a lens will be narrower and its effective magnification will be greater. Nevertheless, the idea of using focal lengths to describe it has stuck, and it’s common to quote ‘effective’ focal lengths when dealing with different camera formats and sensor sizes.
Typically, a lens with a focal length of 35mm or shorter would be considered a ‘wide-angle’, anything in the 40-55mm range would be a ‘standard’ lens, and anything of 70mm or longer would be a ‘telephoto’. Zoom lenses cover a whole range, so a standard ‘kit’ lens for a camera would cover everything from wide-angle to short telephoto.
Maximum aperture
The wider the maximum aperture, the more light the lens captures and the faster the shutter speeds you can use. There are lots of reasons for using smaller lens apertures too, but the maximum aperture is still a crucial selling point.
Prime (non-zoom) lenses will have a single maximum aperture, but zoom lenses will often have a variable maximum aperture. This means that the further you zoom in, the smaller the maximum aperture you have available. For example a camera’s kit lens might have a maximum aperture of f/3.5-5.6 – so that’s f/3.5 at the wide-angle end of the zoom range and only f/5.6 at the long end. This is not ideal and can manual exposure adjustments a little more complicated, but it’s a fact of life unless you have the budget for constant-aperture zoom lenses.
Constant-aperture zooms are preferable but typically bigger, heavier and more expensive. Pro photographers will use a 24-70mm f/2.8 standard zoom because it offers the same f/2.8 maximum aperture right across the zoom range.
Aperture blades
Traditionally, lenses had simpler aperture/iris mechanisms consisting of maybe five or six overlapping aperture blades that would typically produce hexagonal highlights in out of focus areas. There is an increasing awareness today, though, of ‘bokeh’, or the visual quality of out-of-focus areas, and a preference for circular bokeh disks (though there are software tools designed to recreate old-fashioned bokeh shapes with modern lenses – that’s fashion for you).
One of the ways to get this ideal bokeh is to design lenses with perfectly circular apertures, and this is achieved using a larger number of aperture blades, shaped to create a circular aperture. A 7-bladed diaphragm would be considered basic, and there are plenty of lenses with 9 or even 11 blades.
Optical construction
Modern lenses use multiple lens elements within the lens barrel. These can be mounted individually or cemented together in groups. The lens specifications will usually quote x number of elements in y number of groups. Generally, the more elements there are, the more sophisticated the design.
Makers will also draw attention to any specialized lens elements or glass types. Aspheric elements are used to help correct aberrations and are typically GM or ‘glass molded’. You can get ED (extra low dispersion) glass, BR (blue refractive glass) and many more exotic glass formulations, all of which may be quoted as selling points.
Image stabilization
Fewer lenses have built-in image stabilization now because so many newer cameras have their own in-body image stabilization. It’s still a good selling point for lenses to be used on older cameras with no IBIS, like DSLRs, and can also work better for telephoto lenses, even if the camera does have IBIS.
The names vary. Nikon calls its stabilization system VR – Vibration Reduction – so look for ‘VR’ in the lens name. Canon calls its stabiliation IS – Image Stablizer – so look for IS in the lens name.
Autofocus systems
There is A LOT of jargon around AF systems as lens makers constantly develop and improve their AF actuators – the motors that drive the autofocus. Canon uses USM (ultrasonic motor) AF in some lenes and STM (stepping motor) tech in others, and you’ll see this in the lens name. Sony often uses powerful linear AF actuators in its lenses but doesn’t include it in the lens name. Fujifilm, however, does – look for ‘LM’ in the lens name. Nikon used to distinguish between its ‘AF-S’ and ‘AF-P’ DSLR lenses but doesn’t with its later mirrorless lenses. Tamron makes RXD (Rapid eXtra-silent stepping Drive) and VXD (Voice-coil eXtreme-torque Drive) lenses.
As you can see, the jargon around lens actuator and AF systems is practically endless. Generally, more expensive lenses have faster, quieter, smoother autofocus but it’s best to check published lens reviews to get the full picture.
Lens coatings
All lens manufacturers use their own proprietary lens coating systems to reduce internal reflections and flare and maximize image contrast. Nikon alone offers Meso Amorphous Coat, Nano Crystal Coat andARNEO Coat in its lenses. It’s not really possible to say whose coatings are better, so unless you have specific experience of the different types and can make an informed decision, it is just jargon.
It is worth looking out for ‘fluorite’ coatings. These are applied to the front elements of some lenses to resist moisture and grease. This can be especially useful in outdoor conditions and bad weather.
Minimum focus distance/maximum magnification
Here, it’s the maximum magnification figure that tells you the most about the lens’s ability to focus on small objects. It’s usually expressed as a ratio, so a magnification ratio of 1:3 would indicate that the lens can reproduce an object at 1/3 of its real-life size on the sensor. This is a pretty typical figure for a standard zoom, for example. A true macro lens can get right down to a 1:1 ratio, or ‘life size’. Some makers quote a decimal figure instead. For example, Canon makes a series of ‘macro primes’ with a maximum magnification of 0.5x, which would be 1:2 expressed as a ratio. Not ‘true’ macro then, but still a lot closer than most regular lenses.
Physical aperture rings
For a long time, physical aperture rings on lenses effectively disappeared as camera bodies took over aperture control electronically. But now they’re back, and popular with photographers who want to return to old-school camera designs and exposure controls, and with videographers who want to be able to see and adjust the lens aperture while filming, to allow for changing light levels, for example. (In video, the term ‘iris’ is used rather than aperture.) Lenses designed for video will have ‘declickable’ aperture/iris rings.
Filter size
Not the most interesting of lens specifications, but actually very important. High-quality filters are expensive, and it’s useful to choose lenses with the same filter size as ones you have already so that you don’t have to buy multiple sets of filters. If you don’t use filters, this doesn’t matter very much.
Some ultra-wide-angle or fisheye lenses have front elements that are so large and bulbous that you can’t actually fit filters on the front. Some ultra-telephotos, meanwhile, have such wide front elements that filters would be prohibitively expensive, so they use ‘drop in’ filters instead.
Cinema lenses
These are lenses specifically adapted for filmmaking. They will quote ’T’ values rather than aperture values, as this indicates the amount of light actually transmitted through the lens. Cinema lenses may also have geared rings which connect to follow focus units so that an operator can manually adjust the focus while filming without having to grip the lens directly. This is used for ‘follow focus’ and ‘pull focus’ techniques.
