A dome port, when immersed, will becomes an element that interface with the water, its curvature transform’s it into a plano concave lens element which in turn becomes an integral part of the lens underwater optical formula. Therefore, careful consideration should be made to the placement of its position with regard to the lens optical center if one wishes to attain the maximum optical performance of any lenses.
The Aquatica Megadome is a 9.25” port made of the finest BK-7 grade mineral glass stock, finely ground to the highest standard, in order to give you an exceptionally precise lens element to interface with water. Its lens is internally coated with a superior Silicon Oxide coating (SiO2) and a Broad Band Anti Reflective (BBAR) coating. The SiO2 coating is a more resistant type of coating than that used by most other manufacturers, it also has a 0.01% reflective index, providing unparalleled light transmission among its competitors. Another important feature of SiO2 coating is that it’s a perfect match to the index of water, which naturally lowers reflections. Both the SiO2 and BBAR coatings not only assist in preventing internal reflections but also protect the delicate internal surface from scratches. Additionally, to adjust the dome port to a lens properly, Aquatica has an extensive range of port extensions at your disposition, for setting up the Megadome port with the lens of your choice. 
As its name implies, the Megadome is large, and was designed to extract the maximum optical performance from the top quality lenses used on full frame camera by today’s underwater photographers.
The Megadome, with its generous radius and its BK7 glass lens element is the ultimate tool for over/under images. Water droplets do shed faster on glass than they would on acrylic dome ports, and the large diameter means that a visually more appealing and thinner water line will result, and that it is far easier to attain the required depth of field necessary to have both the underwater subject and the surface background in focus than it would be with a smaller radius dome port.
A rugged dome shade is integrated to the design and its extended petals allow the housing to be placed face down, safely keeping the front glass element protected, and a useful characteristic when work, such as battery or memory card replacement on the camera housing is required.  The neoprene cover included with this dome port protects the entire surface of the dome.
The Megadome 9.25” dome port, when used in combination with our comprehensive line of extension rings, will accept a lenses ranging from the moderate wide angle to the extreme fisheye lenses. Our lens chart section will inform you of the chart associated with your camera housing and of the necessary and recommended accessories for using this dome port with your preferred housing.