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Lenses

AF-S DX 12-24mm f/4G

Simon Stafford reviews the first lens in the new Nikkor DX-series.
All text and pictures by the author.

During the past couple of years, in response to feedback from photographers wanting to exploit the full potential of their existing 35mm format wide-angle lenses, a number of manufacturers including Canon, Contax, and Kodak have been consumed in a race to produce a digital SLR camera with a sensor the same size as a full (24 x 36mm) 35mm film frame. Nikon have bucked this trend and adopted an alternative approach by retaining their existing small-format digital sensor and introducing a new class of Nikkor lenses to compliment it.

The AF-S DX 12-24mm f/4G lens on a D100
The AF-S DX 12-24mm f/4G lens on a D100
Lifeguard Trooper
Lifeguard Trooper. D100 (ISO200 NEF RAW) 12mm f16 1/250

Production of this first lens in the new DX-Nikkor series is a clear signal from Nikon that it has no intention of producing a digital SLR with a sensor the same size as a 35mm film frame. The AF-S DX 12-24mm f/4G has an optical configuration that is optimised (see later for a full explanation) for the smaller digital sensor (15.6 x 23.7mm), as used in the D1-series and D100 cameras, which Nikon have named the DX format. This commitment to a small-format sensor should bring several advantages. The principle one is that shorter focal lengths are required for any given angle-of-view (AoV), meaning that the lens can be designed to be smaller and lighter. On the product information sheet for the new lens Nikon go as far as providing a line drawing of the DX-Nikkor and a hypothetical 35mm format equivalent to demonstrate the difference in size. This advantage may be slight with wide-angle to medium focal lengths but will be a major factor for fast telephoto optics.

The lens has its full designation displayed on the barrel
The lens has its full designation displayed on the barrel

The early generations of digital SLR cameras all had sensors smaller than a full-frame of 35mm film but used lenses designed for this format. These small-format digital sensors only cover the central portion of the image projected by 35mm format lenses, and consequently their effective field of coverage is reduced. Since reduction has rather negative connotations the marketing gurus turned the facts around and began making claims about the “increase in focal length” that a small sensor brings about. Advertisement copy would have you believe that by mounting your 35mm format lens on a digital SLR it magically metamorphosed into a lens with a focal length increased by a factor of between 1.3x and 1.6x depending upon the particular brand of camera. Of course this is nonsense! The focal length of the lens remains the same, what changes is the effective AoV.

This trait has been exploited to good effect by news for sports and wildlife photographers, because a 400mm lens used on a Nikon D-SLR covers the same field as a 600mm focal length on a film camera but without any compromise of the minimum focus distance or maximum aperture. However, at the other end of the focal length range even an ultra-wide 14mm lens only provides an angle of view equivalent to a 21mm lens with the DX format. The DX 12-24mm addresses this restriction by offering D-SLR users a range of AoV equivalent to a focal length of 18-36mm on the 35mm (135) format.

Specification

True ultra-wide angle photography is now possible with the Nikon DX digital format digital cameras
True ultra-wide angle photography is now possible with the Nikon DX digital format digital cameras

The 12-24mm is a two-ring zoom. Its barrel is finished in the familiar black, hammered metal effect finish used on all high-grade Nikkor lenses. It has a constant maximum aperture of f/4, seven blades in the diaphragm, and a focal length range of 12-24mm providing an AoV between 99° - 61° with the DX-format sensor. Although the lens has a standard Nikon F bayonet and can be mounted on Nikon film cameras it will only project an image to cover the full 35mm frame at focal lengths between 18mm to 24mm. As the focal length becomes shorter there is an increasing loss of illumination in the corners of the frame. By the time you reach 12mm the image is so heavily vignetted that it is nearly circular (see sample images). The lens has no less than three aspherical elements and two others made of Extra-low Dispersion (ED) glass to help control the path of the light exiting the lens whilst reducing the effects of chromatic aberration to a minimum. The usual Nikon signature of a narrow gold coloured band around the outer lens barrel denotes use of ED glass.

At 12mm on an F100 film camera the image is nearly circular
At 12mm on an F100 film camera the image is nearly circular
At 15mm the image is still pronounced darkening at the corners
At 15mm the image still has pronounced darkening at the corners
At 18mm the lens finally covers the full 35mm film frame with just a hint of darkening at the corners
At 18mm the lens finally covers the full 35mm film frame with just a hint of darkening at the corners
At 20mm the lens covers the full 35mm frame
At 20mm the lens covers the full 35mm frame
At 24mm the image is evenly illuminated
At 24mm the image is evenly illuminated

The lens has a similar profile to the current AF Zoom-Nikkor 18-35mm f3.5-4.5D IF-ED with a wide flange at the front. This has a 77mm filter thread and the bayonet mount for the lens hood. Similar to the design of the AF-S 24-85mm f3/5-4.5 IF-ED the manual zoom ring is at the front and turns counter-clockwise to shorten the focal length. It is marked for focal lengths of 12, 15, 18, 20, and 24mm. The focusing ring, which is the same width at the 24-85mm lens, is closest to the camera body. Immediately behind the focus ring is the focus distance scale set below a window. In common with many recent Nikkor lenses there are no depth-of-field scale markings or infrared focusing index point.

G-type lenses have no aperture ring. The electrical contacts can be seen around the lens mount
G-type lenses have no aperture ring. The electrical contacts can be seen around the lens mount

The use of an internal focusing (IF) mechanism means that the overall length of the lens does not change with the focus action. The front outer barrel section with the lens hood bayonet and filter ring does not move, however, the front element rotates and moves forward within the barrel as the focal length is shifted to 12mm.

On the left side of the barrel (as seen from the camera) there is a focus mode selector switch for either fully manual, or Nikon’s A/M mode that allows instantaneous switching between AF and manual focus control. At 30cm the minimum focus distance is impressive, and the lens can achieve a maximum reproduction ratio of 1:8.3. Finally, as a G-type Nikkor lens there is no aperture ring, and aperture values must be set from an appropriate camera body via one of the command dials.

Handling

The comparative size of the AF-S 17-35mm f/2.8D (right) to the AF-S DX 12-24mm f/4G
The comparative size of the AF-S 17-35mm f/2.8D (right) to the AF-S DX 12-24mm f/4G

A short, squat lens 12-24mm fits comfortably in the hand. At 485g Nikon’s claims about it being proportionally smaller and lighter seem to hold true when you compare it with the other two Nikkors offering equivalent coverage; the 18-35mm f/3.5-4.5G weighs 370g, whilst the 17-35mm f/2.8D is a hefty 745g. The broad zoom ring provides a good platform for a secure grip and turns with a well-balanced resistance. The internal focusing system ensures a very short throw of about a quarter turn to shift from infinity to the commendably short minimum focus distance. In conjunction with the Silent Wave Motor this provides a very swift and positive AF response. My only real complaint concerning the handling is with the manual-focusing ring. The review sample demonstrated a smooth action, however, it is rather narrow, has a low profile, and its location behind the zoom ring makes manual focusing less than intuitive for anyone used to the more common layout on Nikkor zooms with the focus ring to the front. Time after time my fingers would instinctively move forward to adjust focus only to find I had seized the zoom ring instead!

The DX 12-24mm f/4G uses the HB-23 lens hood
The DX 12-24mm f/4G uses the HB-23 lens hood

I am pleased that Nikon have opted for a 77mm filter thread for compatibility of filter size with many other current Nikkor lenses. The lens has a dedicated petal shaped hood, the HB-23, which it shares with the 18-35mm and 17-35mm lenses. The hood has a bayonet fit and locks into place with a firm positive action. The new style LC-77 front lens cap has a centre pinch type of clamp that allows the cap to be taken on and off with the lens hood in place, and helps to give it a more secure fit.

It is interesting to note that Nikon enclose an information sheet along with the instructions concerning the use of ultra wide-angle AF Nikkor lenses, which states that under certain circumstances auto-focus may not work properly. It describes two situations that may cause this to happen. The first is when the subject in the focus brackets is relatively small, and the second when the main subject is a fine pattern. So make sure the AF bracket area is completely, or at least nearly, covered by the subject.

There are a couple of limitations that are also worth mentioning. The shortest focal length that can be used with the built-in flash unit of the D100 camera is 20mm, and the lens is incompatible with all Nikon teleconverters, extension tubes (PK and K-type), and bellows focusing units.

Optical Performance

Church Arch
This elaborate archway was shot at 12mm with an exposure 1/250sec f/8 using a D100 set to ISO200 and NEF RAW. The red box defines the enlarged section of the accompanying picture
Church Arch
This picture (shown at 100%) represents the cropped area from the previous picture. It was shot with camera sharpening set to Normal but no further post processing, and gives an indication of the resolution this lens can achieve with good technique

This is a very complex lens comprising 11 elements, with three aspherical types and two made of ED glass, in seven groups. Overall the optical performance is excellent; in fact at 24mm I would suggest it is outstanding. Images are crisp with plenty of contrast regardless of focal length and predictably at their very best in the middle aperture range. The specialist elements have been included to minimise the effects of chromatic aberration (colour fringing). This generally manifests itself as a coloured ‘halo’ around fine details that exhibit a high frequency change between distinctly different colours or tones. The overall performance of the 12-24mm was truly excellent in this respect. If I am going to split hairs there was evidence of slight chromatic aberration, which required very close scrutiny to be seen, towards the outer field areas at focal lengths less than 15mm but it was not perceptible in the centre of the field.

Church Pillars
Look at the left hand edge of this shot and you can clearly see the barrel distortion that occurs at 12mm and f/4

Geometric distortion, which causes straight lines to be rendered as curved, is very well controlled. At 12mm there is visible barrel distortion (lines appear to bend out toward the edge of the field), which is particularly pronounced at f/4 where there is a noticeable increase in the arc of the line as it approaches the extremities of the field. So avoid this combination if you are shooting critical subjects such as architecture. The level of distortion between 18 - 20mm is negligible making the lens suitable for all subjects but by 24mm there is a hint of pincushion distortion (lines appear to bend towards the centre of the field) although at a much-reduced level compared to the barrel distortion experienced at 12mm.

Poppies
Stopped down the lens achieves a remarkable level of sharpness across the entire field even at 12mm. D100 (ISO200, NEF RAW) 12mm, 1/500 f/11

Predictably at f/4 and 12mm there is also a pronounced curvature of field that results in a perceptible loss of resolution (softness) in the extreme corners of the frame but the centre of the field holds up very well. Stop the lens down to f/5.6 and there is a distinct improvement in the situation, which continues on to a peak between f/8 and f/11. At these apertures I would have no hesitation using the very good close focusing capability of this lens assured that it would achieve a very high resolution across the entire frame, particularly at 24mm.

I mentioned in the introduction that this lens has been optimised for use with the DX-format sensor. I feel it is worth expanding on this point as the design brings a couple of benefits not seen with a 35mm format lens. The Charge Coupled Device (CCD) photo-sites on the camera’s sensor responded most efficiently and effectively to light waves (photons) that strike them at the perpendicular. If a photon strikes the CCD photo-site at a shallow angle not only it is less likely that the photo-site will provide an accurate response to the light energy it is receiving but also adjacent sites are more likely to be influenced adversely by the energy from this photon.

Telephone
Angle of view at 12mm
Telephone Box
Angle of view at 18mm
Telephone Box
Angle of view at 24mm
Telephone Box
Perspective at 12mm
Telephone Box
Perspective at 18mm
Telephone Box
Perspective at 24mm
Flare
Although clearly present the flare in this shot is controlled extremely well

The filter array in front of the CCD sensor used in Nikon digital cameras has a layer of minute micro-lenses that help to direct the light into the photo-sites; however, beyond a certain angle of approach these micro-lenses may not provide sufficient correction. This problem becomes more prevalent with light waves passing through the outer part of an ultra wide-angle lens designed for the 35mm film format, particularly at wide apertures, and is one of the reasons for the rather unhappy marriage between such lenses and digital camera sensors. To paraphrase the explanation provided to me by a senior Nikon engineer the optical design of this DX-series lens is intended to overcome the problem by causing the light passing out of it to be highly collimated, to the point that all the rays are very nearly parallel. Apart from helping to maximise the light gathering capabilities of the CCD sensor, thereby improving final image quality, there is a positive side effect because the sensor receives an extremely even level of illumination across its entire area. Consequently, the DX 12-24mm displays only the merest hint of light loss in the corners of the frame (vignetting) at the shorter focal lengths and widest aperture. Stopped down to f/5.6 and any trace of vignetting in digital images disappears.

Sharpened
The near absence of vignetting is impressive, particularly between f/5.6 - 16, D100 (ISO200, NEF RAW) 24mm, 1/500 f/8

Finally, neither flare, nor ghosting is an issue with this lens, which demonstrates the highest resistance to both of any AF Zoom-Nikkor that I have used. This is an outstanding achievement and means shooting into the light should hold no fears provided you remove any filter to prevent internal reflections from its inner surface, keep your lens spotlessly clean, and use a small aperture to reduce the size of any residual ghost spots to a minimum.

Churchill
The availability of an ultra-wide angle of view allows you to experiment with dynamic compositions

Conclusion

Cottage
The DX 12-24mm delivers images that are sharp, high contrast, and full of rich colour

To be candid I was not sure what to expect from this lens but I am delighted to report that it is full of pleasant surprises. The professional build quality and very positive feel in the hand inspire confidence. My concerns with the manual focus ring are rooted in personal preference based on my way of working and would not necessarily be an issue for another photographer.

It may be the newest kid on the block but thanks to its optics this lens is fast becoming a member of that exclusive club of top drawer, professional Nikkor lenses. At 24mm it surpasses my fixed AF 24mm f/2.8D, which is no mean achievement, and it continues to impress all the way down through the shorter focal lengths. Pick your way with care through the odd performance bramble at 12mm, which are at their thorniest with the lens wide open, and you soon reach the gate at f/5.6 that leads to a lush verdant meadow beyond. It is from here, between 15mm and 24mm that images positively sparkle like sunlit dew, sharp, bright, and full of contrast through the apertures to f/16. Beyond this point the inevitable effects of diffraction begin to take their toll so I suggest you avoid the soft marshes at f/22. If this first offering in the DX-series is indicative of what is to follow I for one cannot wait to see what Nikon have up their sleeve!

Big Ben
I used some fill flash from the D100's built-in Speedlight to lift the shadows beneath the Underground sign. The converging verticals, typical of a heavily tilted wide-angle lens contribute to the sense of height of the subjects, D100 (ISO200, NEF RAW) 15mm, 1/160 f/16

If you cut through all the undergrowth of hype and hysteria and spend a few moments reflecting on the reasons behind Nikon choosing the path they have taken you soon realise it is both a shrewd and prudent move. Their designers and engineers are no longer fettered by the traditional methods of 35mm but have an opportunity to explore and fully exploit the uncharted lands of this new imaging technology. For a relatively modest sum, considering the overall cost of full transition to digital capture, existing customers will be able to add the DX 12-24mm to resolve the issue of wide-angle coverage, whilst continuing to use their existing longer 35mm lenses for many years to come. New customers who start off down the digital road, and have no requirement for film, will be able to embrace other lenses along the way as they are added to the DX range. As the inexorable expansion of digital imaging continues the future is bright the future is DX!

Lens on D1X
Made for each other; the DX12-24mm and the D1X

Likes

  • A true ultra-wide angle-of-view for the DX format digital sensor
  • Optical performance, especially between 15-24mm and f/5.6-f/11
  • 77mm filter compatibility
  • Non-rotating filter attachment ring
  • Compact size
  • Relatively low weight
  • Build quality

Dislikes

  • Narrow manual focus ring
  • Location of focus ring behind the zoom ring

Specifications: AF-S DX 12-24mm f/4G IF-ED

Focal length: 12-24mm (18-36mm equivalent 135 format)
Aperture range: f/4 to f/22
Lens construction: 11 elements/7 groups (two of ED glass)
Picture angle: 99° - 61° (with D1 series / D100)
Focus distance: 0.3m (at all focal length settings)
Max. reproduction ratio: 1:8.3
Attachment size: 77mm
Hood: HB-23 (bayonet fit)
Dimensions (D/L): 82.5mm x 90mm
Weight: 485g

All text and pictures © Simon Stafford
July 2003
www.simonstafford.co.uk


Lens Preview

Simon Stafford provides an exclusive preview of the first DX-Nikkor lens.

The first couple of generations of digital SLR cameras had sensors smaller than a full-frame of 35mm film. Consequently, the effective focal length of a lens was increased by a factor of between 1.3x and 1.5x depending upon the particular brand of camera.

Lens size demonstration
AF-S DX 12-24mm f/4G IF-ED.

This was good news for sports and wildlife photographers using Nikon D-SLR cameras as their 400mm f2/8 lens became, effectively, a 600mm f/2.8, but at the other end of the focal length spectrum even an ultra-wide 14mm lens could only offer an angle of view equivalent to a 21mm lens.

Recently, in response to feedback from photographers wanting to exploit the full potential of their wide-angle lenses, many camera manufacturers have been consumed in a race to produce a digital SLR camera with a sensor the same size as a full-frame of 35mm film.

Nikon have bucked this trend and adopted an alternative approach by retaining their DX-format CCD (23.7 x 15.6mm) and introducing a new class of DX-Nikkor lenses designed specifically for their D1 series and D100 SLR cameras. The lens is optimised for the size and light gathering characteristics of the CCD sensor.

Lens mount
This lens has the same 'F' mount as other Nikkor lenses, but can only be used with the D1 series and D100 SLR cameras. As a G type lens it has no aperture ring.

The first DX lens is the AF-S DX 12-24mm f/4G IF-ED, which is expected to be available in the UK from mid-April. The lens has no less than three aspherical elements and two others made of ED glass to control the effects of chromatic aberration. A two-ring zoom, it has a constant maximum aperture of f/4, seven blades in the diaphragm, and offers a focal length range equivalent to 18-36mm on a 35mm film camera, but due to the smaller image circle this lens projects it can ONLY be used on Nikon’s digital SLR bodies. That said, you can fit the lens on a film camera, however, set to 12mm it projects a circular image with no illumination in the corners of the frame. From 18mm and above the image circle appears to be large enough to cover the entire film frame.

I am very grateful to Nikon (UK) for loaning me a very early prototype, which was issued with a caveat that the design of the optics and internal mechanisms are still being refined and, therefore, I can only offer a preview of the lens. A full review will follow as soon as a final production prototype becomes available.

The lens has a similar profile to the current 18-35mm f3.5-4.5D IF-ED lens with a wide flange at the front, which has a 77mm filter thread and the bayonet ring for the lens hood. Following the design of the AF-S 24-85mm f3/5-4.5 IF-ED the manual zoom ring is at the front and turns counter-clockwise to shorten the focal length. The focusing ring, which is the same width at the 24-85mm lens, is closest to the camera body. Immediately behind the focus ring is the focus distance scale set below a window. In common with many recent Nikkor lenses there are no depth-of-field scale markings or infrared focusing index point.

Lens designation
The full lens designation is laid out around the focus distance scale, which lacks both depth-of-field markings and an infrared focusing index point.

The use of an internal focusing mechanism means that the overall length of the lens does not change with the focus action. The outer barrel section with the lens hood bayonet and filter ring does not move, however, the front element rotates and moves forward within the barrel as the focal length is shifted to 12mm.

On the left side of the barrel (as seen from the camera) there is a focus mode selector switch for either fully manual, or Nikon’s A/M mode that allows instantaneous switching between AF and manual focus control. At 30cm the minimum focus distance is impressive, and the lens can achieve a maximum reproduction ratio of 1:8.3. Finally, as it is a G-type lens there is no aperture ring, and aperture values are set from the camera body via one of the command dials.

Lens serial no
The lens specification and serial number are shown on the underside of the barrel. This very early production prototype of this lens carries a low serial number (No. 200010).

Mindful of the caveat concerning the unfinished optics and mechanics I tried the lens briefly on a D100. My first impressions are of a short, squat lens that fits comfortably in the hand, although I found the manual focus ring rather narrow. The Silent Wave Motor provided a very swift and positive AF response. I am also pleased that Nikon have opted for a 77mm filter thread for compatibility with many other current Nikkor lenses, and it has a dedicated petal shaped hood, the HB-23.

To demonstrate the increase in angle-of-view offered by the shortest focal length I have included two shots for comparison: one taken at 18mm and the other at 12mm.

At 18mm
Due to the smaller format of the CCD used in Nikon digital SLR cameras wide-angle lenses have a restricted angle of view. This is the area covered by a focal length of 18mm on a D100, which is effectively a 27mm lens on the 35mm film format.
At 12mm
The 12mm focal length of the DX-Nikkor offers the same coverage as a 18mm focal length on the 35mm film format.

Specifications: AF-S DX 12-24mm f/4G IF-ED

Focal length: 12-24mm (18-36mm equivalent 135 format)
Aperture range: f/4 to f/22
Lens construction: 11 elements/7 groups (two of ED glass)
Picture angle: 99° - 61° (with D1 series / D100)
Focus distance: 0.3m (at all focal length settings)
Max. reproduction ratio: 1:8.3
Attachment size: 77mm
Hood: HB-23 (bayonet fit)
Dimensions (D/L): 82.5mm x 90mm
Weight: 485g

All text and pictures Copyright © Simon Stafford
February 2003