I'm assuming you mean this: Raynox DCR-2025, Pro 2.2x Telephoto Lens for Digital Still Cameras. In this case, beware of the word "pro", as it doesn't mean anything — Raynox just sticks that on all of their similar products to make them sound fancier. It's also disingenuous and confusing for Raynox to call this a "telephoto lens", because it isn't really.

This isn't a stand-alone lens, but is rather a "teleside converter" made to increase effective focal length of a "real" lens. It's made to give additional options for digicams and camcorders without interchangeable lenses, and it works by using lenses to increase the width of the incoming beam of light. You could conceivably use this on an SLR lens, but I don't think you want to.

In general, they're not really a good deal, since even when you can't change lenses, you can often get better image quality just by cropping. That's because the additional optics destroy detail, so you loose image quality. Might as well lose image quality for free by cropping the image to just the detail you're interested in.

If you really want to use a teleconverter, the kind which goes between your primary lens and the camera usually offers better image quality, although that kind also restricts the effective aperture. But I think probably what you actually want is a real telephoto lens.