Thursday, February 28, 2013

Alphabetti spaghetti - Part 2, Nikon lenses

Ever wondered what all those different letters and abbreviations in the name of your lens actually mean? Well, here's our easy guide to the lens manufacturers' terminology. Part 1 covered Canon lenses, and in part 2 we look at Nikon lenses.

AF - Denotes that the lens uses Nikon's first-generation autofocus system, invented in 1986. It requires an autofocus motor in the camera, and uses a mechanical coupling between the camera and the lens.
(Not all DSLRs have autofocus motors built into them - it's omitted as a cost-saving measure in the smaller/cheaper DSLRs - so AF lenses will not autofocus on every camera. Cameras which have built-in autofocus motors can be identified by the mechanical coupling at about 7 o'clock on the lens mount.  Cameras without this can still use AF lenses, but in manual focus mode only.)

AF-S - Denotes that the lens uses Nikon's second-generation autofocus system. It uses an autofocus motor built into the lens to offer fast and silent autofocus. Every Nikon DSLR supports AF-S.
(This system was introduced in 1996. That sounds to me pretty much like an admission that, in retrospect, their first-generation autofocus was a bet on the wrong technology.)

D - Indicates that the electronics in the lens tells the camera the distance at which it's focussed, which in some situations allows the camera to make better decisions regarding exposure.
(All AF lenses introduced since about 1992 have been D-type, and are sometimes written AF-D.  All AF-S lenses and all G lenses incorporate the distance functionality, but they don't brag about it.)

DC - Nikon's totally unique, patented, Defocus Control. It's only available on a couple of specialised lenses, and it allows photographers to control the bokeh (the quality of the out of focus areas) in their images. It's a subtle effect - it is not the same as 'soft focus' - but it can be great for portraits.

DX - Denotes that the lens is designed especially for cameras with 'crop' sensors, which are conveniently designated by Nikon as 'DX' cameras.
(The key thing about DX lenses is that they don't project an image circle large enough to fill a 'full frame' sensor. DSLRs with full-frame sensors - see 'FX' below - detect when a DX lens is fitted to them an they can automatically crop the image, but putting a DX lens on an FX cameras is like buying a Porsche for the school run.)

ED - Stands for Extra-low Dispersion, and it refers to a type of glass which Nikon invented back in the 1970s. ED glass provides better correction of chromatic aberrations than "lesser" glass.
(Originally ED glass was only used in Nikon's high-end lenses, particularly telephotos. But over time it's filtered down into even their kit lens - the AF-S DX 18-55mm f/3.5-5.6 G ED II - so these days it's pretty useless as an indicator of quality of the lens.)

F - Nikon's standard SLR/DSLR lens mount, which was introduced in 1959, is known as the F mount.
(Until recently you didn't have to worry about this. All Nikon interchangeable lenses were F mount, so it went without saying - it's not written on the lens, or its box, or the camera, or anywhere. And then they introduced the 1 mount for their mirrorless cameras...)

FX - This is actually a designation for cameras, not lenses. It denotes that a camera has a 'full frame' sensor, the same size as a frame of 35mm film (i.e. 36mm x 24mm).
(You might think that lenses which are designed for FX sensors would be called FX, but you'd be wrong. They're not called anything. The reason is that Nikon lenses from the 70's, 80's and 90's were designed for film cameras, so they work on FX sensors, but that was long before Nikon ever coined the FX/DX terminology. So a lens is DX if it says DX, and it's FX if it doesn't say DX.)

G - G-type lenses don't have rings around them to allow you to control the aperture manually.
(All DSLRs support G-type lenses, but some film SLRs don't.)

IF - Internal Focussing. It means that when the lens is focussed (either automatically or manually), all the moving parts are internal. The lens barrel doesn't extend or rotate.
(IF is handy for two reasons. It means you can use filters such as grads and polarisers easily, because they don't rotate when you focus. And it means the lens isn't shifting huge volumes of air around, so hopefully it will be less prone to dust incursion. Unfortunately Nikon have given up being consistent about whether to metion that a lens is IF, so these days you can't tell without doing some research. For example the AF-S 70-200mm f/2.8 G IF-ED VR is clearly IF, but the AF-S 70-200mm f/2.8 G ED VR II is also IF.)

N - Nano Crystal Coat. This is an anti-reflective coating, applied to some of the optical elements of a lens, which reduces internal reflections, ghost and flare.
(Lenses with Nano coating can be identified by a stylised 'N' within in a gold hexagon on the nameplate of the lens. Its not part of the name of the lens, so you need to do some research if you want to figure out whether or not a particular lens has it.)

PC-E - This denotes a perspective control (a.k.a. tilt-shift) lens. Tilt movements alter the angle of the plane of focus relative to the sensor plane, which makes broad depth-of-field possible even at larger apertures. Shift movements slide the optical axis of the lens along the sensor plane, enabling photographers to correct or alter perspective. All Nikon PC-E lenses are manual-focus only.

SWM - This stands for Silent Wave Motor and it's a description of the technology which is used in AF-S lenses.
(You'll see this written on lenses, and in Nikon's marketing blurb, but - unlike virtually all of the other terms here - it's not part of the name of the lens. It doesn't have to be: SWM is completely synonymous with AF-S.)

VR - Vibration Reduction. This is a technology incorporated into some lenses (mainly telephoto lenses) to cancel out the effects of hand-held camera shake. It allows you to shoot with slower shutter speeds without suffering from image blurring caused by camera shake.
(The first implementations of VR offered up to 2 stops of shutter speed improvement: for example, if you could shoot at 1/500th without suffering from camera shake without VR, then the VR system would let you shoot at 1/125th. Newer systems offer up to 4 or even in some lenses 5 stops of improvement, so you could shoot at 1/15th instead of 1/500th! Unfortunately there's no way to tell just from looking at the lens how good the VR is. You have to do a bit of research.)

VR II - Some people think this denotes Nikon's 2nd-generation (i.e. improved) VR system, but it ain't necessarily so.
(True, some lenses have been updated to receive more effective VR systems, and sometimes that's reflected in their names. For example the only differences between the AF-S 200-400mm f/4 G IF-ED VR and the AF-S 200-400mm f/4 G ED VR II are that the latter has an improved VR system - plus incidentally it has Nano coating and it still has IF. But on the other hand the AF-S 70-200mm f/2.8 G ED VR II is a completely different lens from the AF-S 70-200mm f/2.8 G IF-ED VR, so in that case the 'II' seems to apply to the lens rather than the VR. And finally the new AF-S 70-200mm f/4 G ED VR has probably the best VR system Nikon have ever made, but it's just 'VR' rather than 'VR II' or even 'VR III'. Confusing, isn't it?)