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High power binoculars are a very useful tool for birding. Not all birding is done at low powers and at close hand – warblers outside your kitchen window, backyard birdfeeders, etc. Some birding is done at long distances – ducks swimming at the opposite side of a lake at evening, nesting eagles, shore birds, hawks circling high overhead, etc. For these kinds of birding, higher power and larger aperture binoculars are better to let you see the detail you need to make a positive ID.

But it’s hard to hold a conventional high power binocular steady enough to examine a distant bird at length. Your arms soon get tired (not from the weight of your binocular, but from the effort of holding up the weight of your arms for long periods). You develop unavoidable hand tremors that blur the images and fuzz the details. No more. Canon image-stabilized binoculars make those blurred high power images obsolete. Their rock-steady and unblurred images mean there is not only more detail to see, and see clearly, but there is also minimal eye fatigue to tire you out and bring on headaches.

The Canon 30mm and larger IS (active Image Stabilized) binoculars have two Vari-Angle Prisms located between the objective lenses and the image-erecting prisms If the binocular tilts quickly (from even minor hand tremors, for example), horizontal and vertical sensors detect the motion. A microprocessor adjusts the Vari-Angle Prisms in the right and left sides of the binocular independently to compensate for a tilt of from +/- 0.7° up to +/- 1.0° (depending on the model) – far more motion than any fatigue-induced tremor.

Each prism expands or contracts in a bellows motion to redirect the light path and compensate for the tilt. This instantly and precisely adjusts the direction of the visual path through the binoculars to maintain a perfectly steady and centered image, even while the binocular moves. The result is a clear, high power, hand-held image at the push of a button.

Due to binocular size limitations, the physically large independently-adjusted Vari-Angle Prism assemblies cannot fit into the small Canon 8 x 25mm IS binocular. The 8 x 25mm IS uses a Tilt Image Stabilization system that eliminates the larger, more complex independently driven image stabilization bellows prisms used in higher magnification Canon binoculars. In its place, Canon uses a single floating lens element (the third element in the objective lens system) in each side of the binocular. As the binocular is tilted quickly (from hand tremors, for example), sensors determine the direction and angle of the tilt and moves the floating elements in the opposite direction to redirect the light path and compensate for the tilt. This keeps the image steady, even while the binocular moves.

The diagram below shows the action of the Vari-Angle Prisms and the results you can expect. You can see the changing “bellows” action of the Vari-Angle Prisms (yellow in the diagram) as the tilt of the binocular changes.

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