PROLINE UK, Varifocal & manually adjustable series of dome security cameras have the ability to change the zoom, field-of-view, and focus as per application & need. The way to adjust these settings for dome security cameras are inside the dome and can be adjusted as required. Vari-Focal lens fitted allows you to adjust the aperture on the fly. This leaves less room for error and would also allow you to make changes to the view at a later date. Varifocal lenses come in various apertures. These are the general lens sizes. 2.8-12mm lens, 3.5-8mm lens, 6-60mm lens, and 5-100mm lens. The larger the aperture number, the more zoomed in the image will appear and the greater detail that can be captured. The smaller the aperture number, the wider the view and less detail will be captured. Keep in mind that all lenses have particular. The larger the aperture, the greater the detail, but you will get less of a field of view, so the image will be narrower. The smaller the aperture, the wider the field of view, but the less detail you will get, PR-789 & PR-900 are provided with optimum vari-focal lenses for majority of applications.