Dome port or Flat port?

A commonly asked question is: "Do I use a flat port or a dome port with my lens?"

The rule of thumb is that if a lens can accept a screw-on filter, then it can be shot through a flat port. Because the majority of our photos will be taken above water, a flat port is a natural choice as it will not hinder or alter the optics of your lens. Dome ports are used almost exclusively with fisheye lenses as the extreme angle of view that is inherit in a fisheye lens demands that the lens looks through a dome, otherwise severe vignetting will occur.

Prime lenses work great in a flat port as do standard zoom and telephoto zoom lenses. Ports for zoom lenses can be fitted with a zoom control and most recently, due to the focusing issues required by DSLR cameras while being used in video mode, we have started to offer the option of a focus control in addition to the standard zoom control. This added feature is for photographers who need ultimate control while shooting in video mode.

Due to the extreme angle of view that a fisheye lens encompasses, they will always need to be shot through a dome port. Dome ports will usually feature either a hemispherical dome or a portion of a hemisphere.  Essex has been using a four inch diameter hemisphere on our dome ports for a number of years and this dome has performed very well for our photographers as it is compact and easy to work with. We recommend the four inch dome for photographers who are new to working with a fisheye lens in addition to seasoned veterans who want a small, high quality dome. New to the Essex lineup is our ProDome™ which is made from the sweet spot of an eight inch diameter dome. Only the upper third of the dome is used and this is done to maintain compactness as the entire hemisphere is not needed. Discerning photographers are discovering the ProDome™ as it offers minimal distortion,  from a dome port. In the dive housing field, the eight inch dome is a standard size for under water photography applications as it creates a virtual image that can be easily focused on by a close range focusing fisheye lens. By using the upper third of the eight inch diameter dome, this dome has less curvature than the four inch hemisphere and it will still allow all fisheye lenses to see through it without any vignetting issues.