Features
The internals of this massive zoom lens are impressive, being made up of 16 elements in 13 groups. This includes a low dispersion (LD) front element, an anomalous dispersion (AD) element and three aspherical lenses to correct aberrations across the zoom range. The seven-blade construction has a maximum aperture of f/3.5-6.3 and a minimum of f/22-40.
The new Piezo Drive is noted among the abbreviations in the lens description with the letters PZD. The Piezo Drive is a piezoelectric internal autofocus motor.
A piezoelectric element within the motor is sent ultrasonic signals, which cause it to expand and flex. This isn’t uniform, though, so the otherwise rectangular element is twisted into an S-curve. At one end of the Piezo element is a metal tip that comes in contact with a rotor. As it pulses and flexes with the signal, the tip is moved against the rotor causing it to turn. This process is claimed to be faster, more accurate and quieter than a regular DC motor. Although all ultrasonic motor (USM) AF systems use a form of piezoelectric activity, there are key differences in the use of resonance and movement. Tamron also produces an Ultrasonic Silent Drive (USD) system, which is larger but offers even faster focusing.
The lens also includes powerful optical stabilisation in the form of Vibration Compensation (VC). This has been made lighter and more efficient than previous systems by reversing the position of the magnets and the coil. As the magnets are no longer on the moving element there is less load on the drive system and smaller, lighter magnets can be used. The claimed benefit is up to 4 stops on the available shutter speed, which is particularly handy at longer focal lengths and smaller apertures.
The lens focusing offers auto and manual settings but, on the Canon version tested, this does not allow for a manual-focus override in AF mode. When the zoom is extended the lens is increased to almost twice its length. To avoid lens creep, a lock is featured to hold it in place at its smallest size. The focal distances are marked on the focus ring with a minimum focus of 49cm available across the zoom range.
