Superzoom design
Superzooms use a lot of tech to ensure image quality remains stellar
Any zoom lens represents a bit of a compromise in image quality, compared with a fixed focal length prime. It’s only natural that the bigger zoom range of a superzoom lens tends to result in a greater compromise, especially in terms of sharpness and distortions. But, recent designs aim to capitalize on advances in tech, maximizing performance.
A key element in the design of superzoom lenses is the use of ‘aspherical’ elements. Instead of having the natural curve of a section of a sphere, these specially moulded, or ground elements, have irregular shapes. A single aspherical element can replace multiple spherical elements, greatly reducing the size and
weight of a camera lens, while also potentially increasing quality. Given that Nikon DSLR cameras don’t feature sensor-shift stabilization, another key ingredient in superzoom lenses is optical stabilization. If you want a lens that you can use for shooting on holiday or while travelling, you don’t want to be lugging a clunky tripod around with you everywhere. Effective optical stabilization can be a major asset in getting consistently sharp handheld shots, especially at long telephoto focal lengths. All of the lenses in this Big Test feature stabilization.
We’ve come to accept autofocus as a way of life in digital photography. However, there are various competing systems on offer. All of the Nikon lenses on test use ring-type ultrasonic AF systems. They’re based on a pair of large rings within the lens that are driven electromagnetically at ultrasonic frequencies. Performance tends to be quick and whisper-quiet and there’s a handling benefit too. The focus ring doesn’t rotate during AF, so you don’t need to keep your fingers clear while handholding the camera and lens. Full-time manual override of AF is also available, without the need to switch from AF to MF.
The Sigma lenses on test use ultrasonic motor-based AF systems. These enable a smaller, more compact physical construction but the focus ring rotates during AF and doesn’t allow full-time manual override. AF tends to be slower and more audible as well.