Technical Glossary

Vibration Compensation

Lenses with VC: 

  SP AF 17-50mm F/2,8 XR    Di II  VC  LD Aspherical [ IF]
AF 18-270mm F/3,5 -6,3   Di II  VC  LD Aspherical [ IF] Macro
 AF 28-300mm F/3,5-6,3 XR  Di  VC  LD Aspherical [ IF] MACRO
 SP70-300 F/4-5.6 Di  VC  USD

The VC (vibration Compensation) mechanism is a Tamron development which ensures an effective compensation for camera vibrations. Especially hand-held, low-light and tele photography is susceptible for camera shake and consequent blurred results, due to the required longer shutter speeds.  Under these photographic conditions the VC mechanism can unfold to its full efficiency.

 

The construction principle 

The VC mechanism includes a VC lens elements which moves parallel to the image plane merely via electronic control (See illustration 1). The driving coil unit includes a a position detector which assesses the respective position of the element VC and reports to the control unit. The VC element has three magnets which are driven by corresponding driving coils. In the control unit, two gyro sensors are installed, which grasp the horizontal and vertical vibrations and report them to the micro processor. The VC element is free-floating (two degrees of freedom, and parallel to the image plane) and can therefore compensate for vibrations in all directions.

 

(Please click on the image to enlarge it)   If vibrations occur as shown in illustration 2, a blurred picture originates on the image plane, proportionate to the rotation angle of the vibrations. The gyro sensors grasp the respective vibrations and report the data to the microprocessor. This in turn calculates the rotation angle and passes on the respective control commands to the driving unit which in turn shifts the VC element to counter the direction of the vibration. (The system works at a speed of 4000Hz, meaning that a correction is performed 4000 times a second).

Extremely short response times of the driving unit 

The VC driving unit uses a three-coil system developed by Tamron. The VC element is magnetically held in position, stored on three steel ball bearings.  Since the VC compensating lens element is held in place solely by contact with these bearings, smooth, virtually frictionless movement is assured, providing stabilized viewfinder images and excellent tracking performance characteristic of VC lenses. The result is an extremely short response time on grasped vibrations. Moreover, since the VC lens element moves parallel to the image plane via electronic control alone, the mechanical structure is simplified, and the lens is more compact. This serves the compact design concepts which distinguish Tamron lenses.

 

Vignetting

There are two types of vignetting: natural and artificial. Artificial vignetting is caused by components, such as the iris and fixtures among other things which lie in the optical path. These are to be dimensioned accordingly in the construction of the lens.

With natural vignetting the intensity of illumination decreases towards the image edges. Generally valid is: E (a) =cos4*a with whereas a = angle of view and E = intensity of illumination.