Integral Lens | SIGMA DP2x : Special Contents

A lens with a focal length of 40mm to 60mm on a 35mm film camera is known as a “standard lens” because it delivers natural perspective, close to what the human eye perceives. The usual definition of a standard lens is one that has a focal length close to the diagonal length of the image format. The focal length of the DP2x's lens is 24.2mm, and the diagonal length of the image sensor is 24.86mm. So, the lens used in the DP2x really do deserve to be called a standard lens.

In the past, standard lenses have traditionally been of either the Tessar or the Gauss type. The Gauss type is basically used for larger apertures with high performance. Its disadvantages include susceptibility to saggital coma flare when used with a point light source, and a tendency for the light volume to decrease towards the periphery. The Tessar type, on the other hand, has a simple structure, making it easy to miniaturize. However, its drawback is that it tends not to deliver high performance at larger apertures.

Sigma believes that a photo is only as good as the lens it was taken with. So we decided that the kind of quality we wanted for the DP2x would not be attainable using the traditional techniques used to design standard lenses. We rethought the design from the development stage, and set out in pursuit of the highest possible lens performance. We took the bold step of using a retrofocus lens of the type mainly used as wide-angle lenses for SLRs.

Besides having the excellent telecentricity vital in lenses for digital cameras, this retrofocus lens has many other advantages: for example, this format makes it easy to suppress field curvature and astigmatism, and to ensure that the light volume stays the same right to the periphery. However the lens does need to be longer. Therefore, in order to minimize the total length of the lens while still attaining ideal image quality, we used two groups of lens elements: the group at the front have a high refractive index, and the group at the rear are aspherical glass-mold lenses. This way, we successfully developed a standard lens with a relatively modest overall length, but very high optical performance.

As well as employing a rear-focus system, we used aspherical glass-mold lenses, enabling aberration variation to be minimized. And the elements that make up the DP2x's lens have been treated with a super-multilayer coating that succeeds in keeping ghosting and flare to a minimum.

That's not all. Some of the DP2x's lens elements are hyperchromatic, which enables chromatic aberrations to be corrected to a large extent, without impacting other aberrations. This means that even with a wide-open aperture, the images produced have minimal color flare, and are nice and sharp and crisp, right to the edge. The Foveon X3®, which delivers amazing color resolution, also makes a big contribution to the very high level of “emotional image quality” delivered.

In order to maintain high resolution and contrast from the center of the screen right to the edge, and to allow scope for those cool background-blur effects, we aimed for the kind of MTF and all-round lens performance only available with single-index lenses. We are confident that the DP2x's lens, improved time and time again in the interests of delivering the best possible finished image, encapsulates Sigma's expertise as a leading manufacturer of lenses. The impact of the eye-popping image quality delivered by the DP2x's lens is something you really need to see for yourself.