Tokina ATX840AFDC manual Technology Mechanical

TECHNOLOGY - MECHANICAL

One-Touch Focus Clutch Mechanism

The newly improved one-touch focus clutch allows the focus to be moved quickly and easily from the AF position back into the MF position. In Nikon and Canon mounts, the lens can be set for manual focusing without an AF/MF switch or setting the body to the AF position.

Auto Focus Manual Focus

TECHNOLOGY - MECHANICAL

Aspherical Optics

Standard lenses are made from a combination of spherical lens elements. However, there can be problems with such lenses when light entering at the edges of the lens may not be perfectly focused at the same point as light entering at the center. That presents limits to performance in wide aperture and super wide-angle lenses.Tokina uses aspherical glass elements in many of its lenses. In addition to correcting spherical aberration, these lenses fully correct light quantity and distortion at the edge of the image and provide excellent results when used in combination with floating elements. Through technical cooperation with Hoya, Tokina has succeeded in producing high quality molded glass elements with a greater aspherical shape than any other lens so far. This technique is unparalleled in its technological sophistication and excellence.

Internal Focus System

The two main methods of lens focusing are either the complete straight forward movement of elements (used mainly with single focal length lenses), or the rotation of the entire front lens barrel group (used mainly with zoom lenses). The internal focusing system used by Tokina moves each lens group, but does not change the overall length of the lens - this is especially useful with telephoto designs.

The internal focusing system has a number of advantages, including:

1.Faster focusing

2.Improved handling due to fewer movements near the center of gravity

3.More compact lens designs

4.Superior use of filters as the front filter thread does not rotate

SD (Super Low Dispersion) Glass

Lenses with the SD mark use Super-low Dispersion glass which minimizes the secondary spectrum caused by chromatic aberration. Basically, these lenses use FK01 and FK02 optical materials which gives them SD (APO) qualities. This provides excellent image quality in telephoto lenses of 200mm or more by correcting color aberration across the entire picture and bringing all colors into focus accurately at the film plane.

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