A conditioner for the air in a structure which includes a gravel body beneath a building slab. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides. The zoom adjustment member is operatively connected to a focus adjustment member such that movement of the zoom adjustment member causes the focus adjustment member to move thereby moving both the zoom lens and the focus lens axially. The object is to enable a more-accurate adjustment of the pressure in the primary pressure chamber.