50 50 Usage In Air and In Water

Our unique water corrected DeepPro domed housing for the GoPro was designed primarially first and foremost as an underwater camera housing. As such, the optics were optimized for complete submerged use. The optics are optimized to be sharper and focus closer than any other housing on the market.  Our housing incorporates the “Concentric dome port” system to optically correct underwater. This system has been around many years. It’s a simple solution to the problems encountered when imaging through a flat port.  The explanation below applies to any camera housing, the DeepPro housings, and any larger housing made by anyone, and also applies to the stock GoPro little flat port housing.

The below video was a simple test shot in a local lake. There’s plenty of video on our Video page showing the sharpness and close focusing capabilities when the housing underwater, but this video’s real purpose is to show the in air characteristics. As you can see, the in air subjects ares only sharp when it is about 1 to 2 feet distance away. Items further away fall out of focus at longer distances. This is due to the housings pre-installed close up diopter that is part of the domes underwater optics.  See below as to why this housing has a built in close up diopter and is the only one on the market that has such a system.  This diopter “could” be removed and if you did that in air subjects would be tact sharp.. however  you would experience in water subjects soft and you would lose the close focusing advantage of our housing. If you did that you might as well purchase one of the other less expensive domed GoPro housings on the market.

 

 

 

Concentric Dome Ports – How it Works

The use of the “concentric dome port” to optically correct an underwater camera housing has been around many years. It’s a simple solution to the optical limitations of a flat port.  The explanation below applies to any camera housing, both the DeepPro housings, and any larger housing made by anyone, and even the stock little GoPro flat port housing.

Beware, not all domed GoPro housings are the same. Unless the housing has a very large dome radius, or has a built in close up diopter, the images that you obtain underwater will be… fair to average. Not spectacular.  Read below to learn why.

Your Eyes Behind a Flat Mask or a Flat Camera Port Sees Differently Underwater

The light from the subject travels from the subject to our eyes or to the camera’s lens. When filming in air, the light travels from the subject through air, through the housings flat port, then through the air pocket inside the housing tere is no issue. The light continues on its original path. There is no change of direction and there is no distortion of the image. This is how we look through a glass window, or how a stock GoPro flat port housing works in AIR. It works great, in AIR. See Figure 1.

Fig 1. Air - Flat Port - Air Light Path

Fig 1. Air – Flat Port – Air Light Path

Now, put the diver or the flat port housing in water. Things change.  Now when the light from the subject passes through water, then the flat port, then the air inside the housing two things happen. 1). There is a change of direction of the light. It bends.  It is refracted. 2) At those more extreme incident angles, the widest angles, the light also gets “split” into its component color wavelengths. Much light light passing through a prism, the light is split into various colors. No longer is there a homogenous blend of color wavelenghts. This light splitting is called Chromatic Abberation (CA) and occurs with wide lenses put behind any flat port underwater.  This is why the image is soft on the extreme edges of wide images.

Also, when using a flat port underwater, the Field of View (FOV) becomes narrower underwater by approximately 1/3 or 33%.  due to this refraction. Things looks closer or larger in water. We dont see as wide as we did in air. See Figure 2.

Fig 2. Flat Port Distortion Underwater

Fig 2. Flat Port Distortion Underwater

There is a very simple method to resolve the refraction induced by a dome port.  The “fix”is to always force the light to pass through the port, at a perpendicular angle through the glass. Make the light at every possible incoming angle, even extreme angles, to pass perpendicular through that “window”. and not obliquely. See Figure 3 below.

Fig. 3 The Fix to a Flat Port

Fig. 3 The Fix to a Flat Port

The fix needed is a continuous smooth series of “infinite” flat ports put into a “curved” surface in three dimensions. The solution: the Concentric Dome port.  A dome shaped sphere having a parallel inner and outer surfaces.   A dome with the proper shape, the proper diameter, placed at just the perfect “optical center” or “nodal point” of a lens will remove the light refraction of the image, and correct and reduce teh CA. If done properly, the refraction will be gone and the lost 1/3 field of view is recovered underwater. The camera now sees underwater just as it did in air. The CA is eliminated and the edges of the image will be sharper with more contrast.   See Figure 4.

Fig 4. Concentric Dome Fix.

Fig 4. Concentric Dome Fix.

So, adding a concentric dome fixes some problems, but introduces one odd problem. There is a negative side affect that is caused by putting a dome port in water.  Place a dome in water, water on one side, air on the other, and the water-dome-air combination becomes a type of crude negative lens.

Everything that the eye or the camera sees no longer appears several feet away. Instead the image appears very very close. Just a few inches away.  This is what is called a “virtual image”. The underwater image of any dome port  “appears” to be just a few inches away when viewed by the camera.  This happens to EVERY dome placed in water. Big camera or small.

How far away the virtual image appears is a function of some fun math, but basically the distance varies with the radius size of the dome.  Generally, the smaller the dome radius, the more closer to the camera the virtual image is locate. Also the smaller the dome, the more distorted and tightly curved is the virtual image. With a larger radius dome radius the virtual image is a few inches further away and there is less bend to the virtual image.

In general, larger camera housings with 7-8 inch domes have a virtual image roughly 10-12 or 18 inches away. Much smaller 4 inch domes have a VI that is much closer in, just a few inches away and the image is highly curved meaning that the edges might tend to be slightly out of focus. Most camera lenses are designed to focus on a flat plane, not a curved plane.

Mounting a dome on your housing will restore the lost field of view but now the image might be out of focus. Your camera must be able to clearly focus on the wet domes Virtual Image.  The camera lens MUST be able to focus on that close in virtual image.

VirtualImage OfDome 550px-UW

Fig. 5 Dome Virtual Image and Fix

 

This was a problem in the original GoPro Hero1 housing. It had a small curved dome on the housing and when put underwater images were out of focus as the camera was not able to focus on the domes virtual image.  GoPro then changed to a flat port in later models.No more virtual image. Images in air or water are in focus. However, when placed underwater the light bending and CA problems occurs.

How to Focus on the Virtual Image: Install Reading Glasses.

When mounting a dome port on a larger more expensive underwater camera housings the photographer simply makes sure to use a lens that has a minimum close focusing capability that is able to focus on the domes Virtual Image.  Its a matter of getting the right “size” dome and any necessary spacers (to adjust the domes center to match the len’s center”.

But what about the GoPro camera. Its a great camera, but it is FIXED FOCUS. There is no ability to adjust focus with the GoPro Hero 1-4 cameras.  DeepPro implemented in our GoPro Domed housing a factory installed close up lens in front of the camera’s lens and behind the dome port.  This makes the GoPro able to now see closer and to focus clearly on the dome’s virtual image.

Other people have been doing this for years with larger camera housings. One famous implementation of this solution is the famous Nikonos 15mm underwater Nikkor lens. To many this was the finest underwater lens ever made. It created amazing sharp extreme wide images underwater. It was nothing more than a concentric dome port matched to a very wide and very close focusing lens, all built into one, optimized for underwater use only.  And it cost over $1000 at the time. It worked great.

This is why you will see inside the DeepPro housing a glass diopter already inside in the housing. It is there for forcing the GoPro camera to sharply focus on the dome’s virtual image when underwater.   If you were to take it out, you may get sharp images underwater at far distances, but not as sharp and not at close in distances. If you use the housing out of water, in air, because of the diopter installed, subjects more than a two or three feet away will be out of focus.