The Ikelite dome is injection molded specifically for underwater photography, and represents the finest optics in the industry. Recommended for wide angle lenses from 17mm to 28mm, and short zoom lenses Zoom lenses require a +4 diopter close-up lens available from camera stores. Wide angle lenses will focus at 12" and do not require the addition of any close-up lens when used in a dome port. Other ports available : #5503.... Lens length less than 3" (7.6cm) 5503.50 Lens length less than 4" (10.1cm) #5503.55 Lens length less than 4.5" (11.4cm) #5503.80 Lens length less than 5" (12.7cm) #5503.85 Lens length less than 6" (15.2cm) SUPER-WIDE DOME PORT For lenses with a 110 to 170 degrees angle of coverage. This port does not allow use of a port shade, and may not be fully functional with some lenses in the MD-size housing. #5503.15 Lens length less than 2.5" (6.3cm FLAT PORTS For standard, macro and telephoto lenses. #5501..... Lens length less than 2.5" (6.3cm) #5502...... Lens length less than 3.5" (8.9cm) #5502.41 Lens length less than 4.1" (10.4cm) #5505...... Lens length less than 4.5" (11.4cm) #5505.45 Lens length less than 5.1" (13cm) #5505.5 .. Lens length less than 5.5" (14cm) #5505.58 Lens length less than 6.1" (15.5cm) FLAT PORTS WITH FOCUS For long lenses whose focus collar extends beyond the housing focus #5506.... . Lens leng