Michael -- Not exactly true. While adapters that screw into the front of camera lanses and either reduce or enlarge focal lengths have been around for quite awhile, the focal reducers for astronomical uses fit on the back of the telescope and as their name implies, reduce the effective focal length. The same principle is possible for a camera lens. The question is, why? Unless you want to convert an 18-250mm, to a 13 - 175 for some reason, it's not terrible useful. I believe would also be some penalities in sharpness. And BTW, I think just such a device is available for mirrorless cameras now.