The iDC PhotoVideo SYSTEM ZERO Follow-Focus XL1 With Camera Plate For Canon T3i is a set consisting of a focus wheel, a T3i-specific camera plate and a seven-slot focusing plate. The camera plate attaches to the bottom of the T3i. The focusing plate attaches to the camera plate. And the focus wheel slides into one of the seven dovetail slots of the focusing plate. The O-Ring mentioned above is replaceable yet very tough. A thumbscrew on the focusing plate tightens to keep the O-Ring pressed up against a lens.
When the thumbscrew is loosened, the focus wheel that the O-Ring is featured on can be moved aside, thus facilitating a lens swap. The set is compatible with a very long list of lenses (see specs) because the focusing plate by means of seven slots was designed to accommodate a variety of lens constructions. And for those lenses that fall in-between the dovetail slots, the focusing plate slides for quick micro-adjustments.
The included focus wheel can be used with all iDC camera plates and thereby with DSLRs other than the T3i. The T3i-specific camera plate can also serve useful in adding viewfinders to the T3i; it holds in place via two screws compatible SYSTEM ZERO viewfinders, such as the iDC-modified Hoodman HoodLoupe and thus enables quick-release functionality. The camera plate also accepts the Zacuto Z-Finder Pro when the Z-Finder is equipped with a Zacuto mounting frame. The camera plate in such a case would replace the Zacuto Gorilla Plate.