The Current Issue
Interactive subscribers-only website
AF-S DX 12-24mm f/4G IF-ED
Small is beautiful!
Simon Stafford reviews the first lens in the new Nikkor DX-series.
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.
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 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.
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 18mm the lens finally covers the full 35mm film frame with just a hint of darkening at the corners