Nikon initials decoded
In literature about Nikon lenses and accessories, as well as on the products themselves, you will find various initials and codes. Knowing what those mean may help you better understand the characteristics of the different products.
(If you are interested initials and other codes used by other lens manufacturers than Nikon, you may also want to refer to our alphabet soup guide.)
As an example of the type of codes this article is about, look at the image to the left. It shows a Nikon-lens, and the long name, the label that is marked on the lens, is DX AF-S Nikkor 18-135 mm 1:3.5-5.6 G ED.
I.e.: This particular lens label consists of seven elements, starting with “DX” and ending with “ED”. Below is a brief explanation of each of the seven elements.
- “DX”: This two-letter code is specific to Nikon (and Tokina), and tells us that this lens is a lens designed with to be used on a DSLR with a DX size image sensor.
- “AF-S”: This is a Nikon-specific code, and tells us two things. First, that is an autofocus (AF) lens, and second, that the lens is fitted with a silent wave (S) motor that drives the autofocus.
- “NIKKOR”: This is a brand name for Nikon lenses.
- “18-135mm”: This is the focal lengths of the lens. Since this is a zoom lens, two different values are given. The lens is 18 mm at its wide end, and 135 mm at its tele end.
- “1:3.5-5.6”: These are the maximum apertures of the lens.
- “G”: This is a Nikon-specific code and indicates that a lens is without a mechanical aperture ring and also that it will relay distance information to the body.
- “ED”: This is a Nikon-specific code and indicates that at least one special glass element, called a Extra-low Dispersion element, is used in the lens.
Below, we shall describe these and other elements used in lens labels in much greater detail.
2. Common initials
Below is a more detailed breakdown of the initials letters you will find used to describe Nikon products. Below is a short list of codes with a brief explanation. Clicking on a code
- AF, AF-n, AF-D, AF-G, AF-I, AF-S – Different labels to indicate an autofocus lens.
- AI, AI-S, AI-P, Pre-AI – Aperture Index.
- D – Distance data is relayed to body.
- DC – Defocus Control
- DX – For use with DSLRs with a 23.6 x 15.8 mm sensor.
- E – Economy.
- ED – Extra-low Dispersion.
- FX – For use with SLRs/DSLRs with a 24 x 36 mm, or smaller, sensor.
- G – No aperture ring & distance data is relayed to body.
- IF – Internal focusing.
- IX – Lenses made for the Nikon Pronea APS system.
- Micro – Nikon's designation for a macro lens.
- N – Nano Crystal Coat
- PC, PC-E – Perspective control.
- VR – Vibration reduction.
AF, AF-n, AF-D, AF-G, AF-I, AF-S
The label “AF”, often in combination with another letter indicates that the lens is a autofocus lens. The secondary code letter provides additional about information about the lens:
- AF – Autofocus. Relies on focus motor in body to work.
- AF-n – Never used by Nikon. See below for usage.
- AF-D – As “AF”, but also relays distance data to body. See also this section.
- AF-G – As “AF”, but have no aperture ring, etc. See also this section.
- AF-I – Autofocus with built in-motor (old system).
- AF-S – Autofocus with built in-motor (new system).
Nikon autofocus lenses labelled “AF”, “AF-D” and “AF-G” do not have a built-in focus motor. These lenses instead use a screwdriver-like mechanical coupling where a focus motor in the body transfers torque to the autofocus mechanism in the lens. Nikon's entry level DSLRs such as the D40, D40x, D60, D3000, D3100, D5000 and D5100, do not have this coupling. These lenses will not autofocus with lenses labelled just “AF”, “AF-D” or “AF-G”.
To summarise: Entry level Nikon DSLRs will not autofocus with a a Nikon autofocus lens unless the lens is either of the type “AF-I” or “AF-S”. The more advanced Nikon DSLRs will autofocus with all Nikon autofocus lenses, including those labelled “AF”, “AF-D” and “AF-G”.
To see which lenses will autofocus on all Nikon DSLRs, including entry level models, see this list.
You will only see the “AF-I” label on older lenses. All new Nikon lenses with a built-in focus motor carries the “AF-S label.
Nikon uses the “AF-S”-label for both ring-motor silent wave AF-S and for micro-motor AF-S. However, a micro-motor is not silent and fast like a ring-motor, nor will it let you override with manual focus while in autofocus mode. Micro-motor driven autofocus uses moving mechanical parts, such as cogwheels (gear wheels) and shafts.
For Nikon lenses, a quick way to determine the type of focus motor is to examine the lens' autofocus control panel (show above). A lens equipped with a micro-motor will only let you choose between autofocus (A), and manual focus (M). A lens equipped with a ring-motor will let you choose between manual+autofocus (M/A), and manual focus (M).
The designation “AF-n” has never been used by Nikon, but you may see it in adverts for second hand Nikon lenses. It is used to distinguish between older and newer versions of some of the earliest AF lenses. A lens designated “AF-n” is optically identical to the initial “AF” version of the lens, but has an improved design with a wider rubberised focus ring.
AI, AI-S, AI-P, Pre-AI
Nikon lenses has since 1977 had an automatic aperture indexing feature that eliminated the need to manually align the aperture ring when the lens was mounted. The first lenses to include this feature was also labelled “AI” or “AI-S”. However, all Nikon lenses with an aperture ring that have been introduced after 1977 have automatic indexing, whether these initials is included in the lens name or not. G type lenses have no aperture ring, and therefore do not have aperture indexing.
The main difference between “AI” and “AI-S” is that with AI-S, there is a standardised linear relationship between the movement of the stop-down tab at the rear of the lens and the aperture opening. I.e. moving the tab a known amount stops down the lens to a known aperture. This is required for accurate exposures in shutter priority and program modes on the Nikon FA (1983) and F501/N2020 (1986). Lenses designated “AI” do not do this.
In addition, AI-S lenses will automatically trigger the high speed program mode (where the camera will pick a shorter exposure time for hand-holding) with the FA and F501/N2010 if the focal length is 135 mm or longer.
However, only a few old camera models, such as the FA and F501/N2020 make use of these features. Newer cameras (including the F3, F4, F5, F6, the FE and FM-series and all Nikon DSLRs) treat AI and AI-S as the same. These models do not let the photographer use shutter priority or program modes with any manual lenses. For these models, the AI-S functionality is redundant (unless the lens is “chipped”).
If a manual focus lens is “chipped”, setting the aperture on the body, instead of on the lens itself, only works with an AI-S lens. (For more about “chipping” see Bjørn Rørslett's CPU modification page.)
There exists a few manual lenses with the automatic indexing feature fitted with a CPU chip that sends the lens information to the camera body. Such a lens is referred to as “AI-P”.
Unless the lens is “chipped”, manual focus lenses do not meter with many Nikon DSLRs. The Nikon DSLRs that meter with manual focus lenses without a CPU are D200, D300, D300s, D700, D7000, D1-series, D2-series and D3-series. To use matrix metering with manual focus lenses without a CPU, you need to store the lens' focal length and maximum aperture using the menu. Otherwise you can only use centre-weighted and spot metering.
The term “Pre-AI” refers to a manual focus lens produced before 1977 without the automatic aperture indexing feature. Such lenses may harm many newer Nikon bodies. There are, however, some exceptions. Nikon has never used the term “Pre-AI”, but you will see it in literature discussing Nikon lenses.
Some Nikon lenses relay distance information to body. Older lenses with this feature has a “D” somewhere in their name, either alone, or written like this “AF-D”. Newer Nikon lenses tagged with the letter “G” also relay distance information to the body.
According to Nikon support, distance information (relayed by D- and G-lenses) is important for getting the most accurate exposure from Nikon's flash system CLS (Creative Lighting System). The use of Nikon D- or G-type lenses is recommended as the distance information is used to make the computation of what flash power to use more accurate.
In addition to relaying distance information to the body, lenses labelled “G” can only have their aperture electronically controlled. They have no physical aperture ring. This means that the aperture must be set by the camera. These lenses cannot be used on older mechanical Nikon cameras that require an aperture ring, and they cannot be used with Nikon extension tubes and bellows that have no means of communication electronically with the lens.
The initials “DC” stands for Defocus Control.
The Nikon lenses carrying this label allows the photographer to change the appearance of the out-of-focus portions of an image. It it gives the photographer to some extent control over bokeh. The effect is very subtle and does not affect the in-focus part of the image.
This type of lens is mainly used for portraits.
Note that these are not soft-focus lenses. If the photographer want a soft-focus effect, this must provided by other means, such as a soft-filter in front of the lens or by adding a soft light layer by means of image editing software.
A fundamental characteristic of a lens is its image circle. The image circle is the circle that contains the image projected on to the film or digital sensor.
In the film era, the most popular film format was called the 135-format and produced negatives the measured 24 x 36 mm with a 43.3 mm diagonal. All Nikon film SLRs, and some Nikon DSLRs are designed with an image circle to fit this size. Nikon refers uses the term “FX” for this format. The Nikon DSLRs using the FX-format are the D700, and the D3-series. Nikon labels these cameras “FX”. While the FX-label appears on the DSLR, it never appears in the lens.
Most Nikon DSLRs have a sensor than is smaller than FX-size. Nikon calls this format DX. The DX-size format is designed to cover a digital sensor measuring 23.6 x 15.8 mm, with a 28.4 mm diagonal.
DSLRs using the DX-size format may use lenses that are specifically designed for the smaller area (compared to the FX-format). Nikon always put a “DX”-label on such lenses. Lenses for the DX-size format can be built smaller and lighter than a comparable lens for the FX-size format. A Nikon lens labelled “DX” will physically fit on an FX camera, but its use will result in vignetting in at least part of its focal length range.
Nikon lenses for the FX-format have been manufactured since 1959. Nikon lenses introduced prior to 1977 (“Pre-AI”) may harm newer Nikon bodies (there are exceptions). There also exists Nikon autofocus lenses for the FX format without a built-in focus motor. These lenses will not autofocus with an entry-level Nikon DSLR. Manual focus lenses for the FX format (unless “chipped”) will not only meter with certain DSLRs. However, there also exist many Nikon lenses designed for the FX format or for 135-format film that also work very well on the DSLRs using the DX format, and whose only disadvantage is that they are larger and heavier than their DX counterpart.
Nikon originally targeted the professional market. To appeal to more budget-minded photographers, Nikon in 1979 created a line of lenses called “Series E” (for Economy). They were produced using cheaper materials than Nikon's professional line of lenses. For instance, they frequently include aluminium or plastic parts, while brass and steel was used in the professional grade Nikkors.
Technically, these are AI-S lenses, but Nikon does not label them as such.
Back in 1979 Nikon reserved the name “Nikkor” for professional grade lenses. All the lenses in the lenses in Series E were just labelled “Nikon”. This distinction is no longer valid. Nikon now sells cheap plastic lenses, as well as some very expensive ones, and they all carry the “Nikkor” label.
Nikon no longer make the “Series E”, so you will only find these lenses on the second hand market.
Some lenses uses glass elements such as fluorite (an artificial crystal) or other special types of glass with extra low dispersion. Nikon labels lenses that contain such elements “ED” for Extra-low Dispersion.
The reason that such special glass is used is to correct chromatic aberration. This is particular important in long tele lenses (200 mm and above). These days, one often see a reference to special glass elements in non-tele lenses. This is (IMHO) a marketing gimmick.
Both fluoride and low dispersion glass is less stable with temperature than conventional glass. This means that the optical characteristics of these lenses change slightly with temperature. Nikon colour some of the longer lenses with ED-glass white or light grey to make them less susceptible to temperature change. There is no hard infinity focus stop on Nikon ED-lenses because the point of infinity focus will change with temperature.
Fluoride and low dispersion glass has a lower refractive index than conventional glass, so such designs requires more deeply curved elements for the same focal length, than conventional designs.
Nikon lenses labelled “IX” were produced for Nikon's Pronea APS film bodies at the end of the 1990ies. Although they use the Nikon F-mount they have a deep plastic collar to prevent them for being physically mounted on any Nikon DSLR. If you manage to mount one, the collar protrude into the camera's mirror chamber and may break your camera's mirror. Unless you happen to own a Pronea body, just forget about these.
The label “PC” in a Nikon lens stands for Perspective control. This means that the lens have mechanical controls that gives it the ability to tilt, shift, rise, and fall. This is used to remedy problems such as key-stoning in architecture photography.
Nikon's latest perspective controlled lenses carries the label “PC-E”. The letter “E” here indicates that they have an electronic diaphragm. Traditionally tilt-shift lenses are full manual operation meaning that everything from aperture, shutter, and focus has to be manually set. However, the PC-E versions can be used in Program or Aperture priority modes provided you have a compatible Nikon DSLR (e.g. D300s, D700, D3s or D3x).
In 1976, Nikon first introduced some lenses where focus was achieved by moving elements inside the lens barrel. This was called “Internal Focusing” (IF) and resulted in less glass being moved and therefore faster autofocus than conventional designs. Another benefit was designs with a closer minimum focus distance, that the front element don't move during focusing (useful for macro), and that the front ring don't rotate (useful with certain types of filter).
Internal focusing widens the lens' field of view as it focuses closer. Such lenses will only have the FOV normally associated with its rated focal length when the focus is set to infinity. Focused at its close focus distance (CFD), most IF lenses have a FOV that corresponds to the FOV of a shorter focal length.
Nikon uses the term “Micro-Nikkor” to indicate that a lens is a macro lens (e.g.: “Micro-Nikkor 105mm f/2.8 G AF-S VR IF-ED”).
Also see the section discussing CFD magnification below.
Nikon puts a symbol containing the letter “N” inside an oblong hexagon (see illustration on the right) on the barrel of lenses that features Nikon's Nano Crystal Coat. However, the “N” is not normally used as part of the lens name.
This type of coating is used to cut down on internal reflections to remove flare and ghosting. Nikon claims it is superior to traditional coatings.
Nikon's in-lens stabilisation system is called “VR” (Vibration Reduction).
The purpose of lens stabilisation is to reduce motion blur caused by hand-holding the camera at long shutter speeds. This is done by having a floating lens element which is moved orthogonally to the optical axis of the lens using electromagnets, modifying the optical path to cancel vibrations caused by angular movement of the lens.
Nikon's initial VR-system was introduced in 1994 and allowed the photographer the up to three stops improvement when hand-holding. The current system is called “VR II” and offers up to four stops improvement.
Some Nikon lenses have a switch that let you toggle VR between “Normal” and “Active” mode. Use “Normal” for hand-holding from a fixed position, and “Active” when shooting from a moving vehicle and similar situations.
The VR system does not engage until the shutter is pressed half-way. It may take some time (up to 1 second) before the stabilisation settles and gives you the most stable result.
Note that activating the stabilisation system only affects your ability to photograph a stationary object at longer shutter speeds without getting blur from camera shake. If the object is moving long shutter speeds will give you motion blur whether the stabilisation system is active or not.
3. Optical parameters
The optical parameters that determines the characteristics of a fixed focal length lens are the focal length, the maximum aperture, and the magnification at the close focus distance (CFD).
A zoom lens has always two focal lengths associated with it, indicating the focal length at the start and at the end of the zoom range. The name of a zoom lens may also list two different maximum apertures, then the first is associated with the start of the zoom range, and the second is associated with the end of the zoom range. For a zoom lens, the CFD magnification is always when the zoom is set to its longest focal length.
The focal length of a lens expressed as one or two numbers followed by the label “mm” (millimetres). Examples: “50 mm” and “18-135 mm”.
The focal length is a physical property of an optical system. When a photographic lens is set to “infinity“, its rear nodal point is separated from the sensor or film, at the focal plane, by the lens' focal length.
When the focal length is a single number, the lens is called a fixed focal length lens. When the focal length is expressed as two numbers, the lens is called a zoom lens or variable focal length lens. A fixed focal length lens has a single focal length that cannot be changed. A zoom lens allow the photographer to select any focal length within the range given by the two numbers. For example, a zoom lens designated “18-135 mm” can be set to a focal length equal to 18 mm at its wide end, and 135 mm at its tele end, and also any value between the two extremes.
For a photographer, the focal length is useful to determine the field of view (FOV) he or she will get when using the lens on a camera with a sensor with a given size. For practical and historical reasons, the FOV itself have never been marked on the lens. Instead, the focal length is given, and the photographer is expected to know how focal lengths corresponds to FOV.
For example, if you use a camera that has a DX-format sensor, you may know that a focal length equal to 19 mm corresponds to a wide angle lens with a FOV equal to 75°, a focal length equal to 33 mm corresponds to a so-called normal lens with a FOV equal to 47°, and a focal length equal to 100 mm corresponds to a so-called tele (or tele) lens with a FOV equal to 16°. Notice that the smaller the number designating the focal length is, the wider the FOV.
You should also know that the relationship between a specific focal length and and a specific FOV is only true for a specific sensor size. The FOV angles listed above are all true for a camera with an DX-format sensor, but if you use the same focal lengths on a camera with a FX-format sensor, the FOV angles will be different, as shown in the tables below.
Some people are confused when they encounter a lens that is a reduced image circle lens. They believe that they also need to take this into account to determine the FOV of the lens. This is not so. Setting a specific focal length (e.g. 19 mm) will always produce a FOV equal to 75° when placed on a camera with a DX-format sensor – it does not matter if you choose that setting on a zoom lens designed for a DX-format sensor, or a zoom lens designed for a larger format sensor.
When selecting what lens to use for a task, you should be familiar with the common names used for different classes of lenses (i.e. super-wide, wide, normal, short tele, tele and super-tele), and how these classes of lenses maps onto specific focal lengths depending upon sensor size. This is done in the two tables below.
The table shows the focal length (in millimetres) for for a number of common DSLR formats. The rows labelled “FOV” shows the field of view in degrees for the focal lengths listed. The top FOV row shows diagonal field of view, and the bottom FOV shows horizontal field of view for sensors with a 3:2 aspect ratio (i.e. all except Four-Thirds, which has a 4:3 aspect ratio). You can use the table to figure out the focal lengths to look for if you want a specific class of lens, given the sensor size of the camera you want to use the lens on.
|Format||Crop f.||Super-wide||Wide||Normal||Short tele||Tele||Super-tele|
When using the table, you will need to match focal length to the nearest focal length that is actually available. E.g. if you want a “normal” fixed focal length lens, matching the popular 50 mm on a camera with an FX-format sensor on a camera with a DX-format sensor, the table tells you that an exact match is 33 mm. However, a 33 mm lens does not exist. In this case, you should pick a 35 mm or a 30 mm.
Let's say that you want to buy a super-wide class lens. You can see from the table that for a camera with an FX-format sensor, you need to find a lens where the focal length is 24 mm or shorter. If your camera uses a DX-format sensor, you need to use a lens that is 16 mm or shorter for the same super-wide effect.
This means that a lens such as the Nikkor 14-24 mm will be clearly classified as super-wide for use on a camera with a FX-format sensor, but only marginally so for a camera with a DX-format sensor. If we use this Nikkor with an adaptor on a camera with a Four-Thirds sensor, it will be classified as wide-to-normal (not super-wide).
We can also see from the table that for a camera with a DX-format sensor, you would need a lens with a zoom range 9.3 mm to 16 mm to match the FOV of the Nikkor 14-24 mm when used on a FX-format sensor. Unfortunately, such a lens does not exist for the DX-format, so one must use something like the Sigma 10-20 mm instead. This lens, however, does not go as wide as 114° on the wide end. On a camera with DX-format sensor, f=10 mm gives a diagonal FOV=110°.
While there exists lenses with zoom ranges to goes from wide to tele (e.g. the Canon EF 28-300mm f/3.5-5.6 L IS USM and the Nikon 18-200mm f/3.5-5.6G IF-ED AF-S DX VR), the compromises that is inherent in such designs make many photographers build a collection of quality zooms that covers the range from super-wide (FOV ≈114°) to tele (FOV ≈12°) spread over three lenses. The table below shows the typical zoom lenses in such a collection. The table also shows the diagonal FOV at both ends of the range.
|Format||Crop f.||FOV||Super-wide zoom||Standard zoom||Tele zoom||FOV|
|FX:||1.0x||114°||14-24 mm||24-70 mm||70-200 mm||12.4°|
|DX:||1.5x||110°||10-20 mm||17-55 mm||50-135 mm||12.0°|
Currently, users of cameras with FX-format sensors have access to original zooms with a maximum aperture of f/2.8 in the FOV-range from super-wide) to tele. For Nikon DX bodies, third party lenses must be used to cover at least part of this range if one want wide or fast zooms.
While FOV is the most important parameter decided by the focal length, the focal length also influences the depth of field (DOF) at a given aperture. But DOF is much more complicated than FOV, so I skip the details. Briefly, a short focal length (small mm-number) gives you a deeper DOF than a long focal length (large mm-number). For a more comprehensive discussion of the relationship between focal length and DOF, see this webpage.
There are many notations in use for indicating the maximum aperture as part of the lens' label. Here is a list of examples: “f/1.4”, “1:1.4”, “F1.4”, or just “1.4”.
All the aperture labels above refers to the same aperture, and the number repeated in all of them (1.4) is often referred to as the “f-number”.
What this boils down to, is that the f-number is a numerical label for a lens' aperture. For more about the f-number and what it means, see our article: The Aperture and the F-number.
When looking at the aperture label for a zoom lens, you may find two different f-numbers. This means that the zoom has a design where the maximum aperture changes when the focal length changes. The two maximum apertures listed are the maximum aperture available at the zoom's lowest and highest focal length. For example the Nikkor 18-135mm f/3.5-5.6 will have a maximum aperture equal to f/3.5 when used with the zoom set to at 18 mm, and it will have a maximum aperture equal to f/5.6 when used with the zoom set to 135 mm. Not all zoom lenses list two aperture values. Some (usually more expensive) zoom lenses provide constant aperture over its entire zoom range. Then only a single maximum aperture is given.
The minimum aperture of a lens is never listed as part of the lens label, but can be found if you look up the manufacturers data sheet for the lens.
A macro lens (called a “Micro-Nikkor” by Nikon) is a lens that is constructed to let you focus on objects very close to the camera. A major characteristic of a macro lens, is its CFD magnification. This tells us the ratio between the real life size of an object, and the projection of that object on to the sensor or film, when the lens is focused as its close focus distance (CFD). Sometimes this datum is referred to as maximum magnification.
The number indicating the lens' magnification is sometimes written as a ordinary fraction (e.g. 1:2) and sometimes a decimal fraction followed by an “X” (e.g. 0.5X). These two are equivalent and both refer to a magnification that is half life size.
A CFD magnification of 1:1 or 1.0X means that the projection of the object on the sensor will measure the same as it does in real life (i.e. life size). If you took a picture of a ruler at magnification 1:1, a 10 mm segment of the ruler would occupy exactly 10 mm on the digital sensor or film negative. A magnification of 1:5 or 0.2X means a fifth of life size, and a magnification of 3:1 or 3X will magnify the object to three times life size, and so on.
Most photographers do not classify a lens as a real macro lens unless it has a construction that is corrected to provide a flat field at close range, and that its CFD magnification is at least half life size. Most real macro lenses has a CFD magnification of life size.
In the macro region (i.e. at and around a 1:1 magnification) the depth of field will be very shallow, and it will be determined by magnification, not focal length. In other words, there will be no difference between the depth of field of a 50 mm lens and a 150 mm lens if both are used at life size (1:1 or 1.0X) and both are set to the same aperture.
4. Lens hoods
Nikon lens hoods are labelled with two initials, followed by a number. The first initial is always “H” and the second is either am initial of a Japanese or and English words which indicating the type of hood. Here is the initials used:
- HB – Bayonet mount hood.
- HE – Extension hood for long lenses that already have a hood.
- HK – Kabuse = slip-on lens hoot. Locks using a knob.
- HN – Nejikomi = screw mount lens hood.
- HR – Rubber lens hood, usually screw mount.
- HS – Snap-on lens hood. Attaches to lens like a lens cap.