Underwater Optics Expertise
Underwater photography has this particularity to be done in a really wet atmosphere.
The main issue is that your cameras and lenses are made to stay dry.
We need to place those components in a safe waterproof housing and make the images trough a transparent window.
This window can be :
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Flat, a flat port
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Spherical, a dome port
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It can also be a lens, we have the expertise to calculate it if it’s really necessary.
Using a flat port:
Refraction
As the light change of medium from water to air, it’s refracted. It’s the case when you put a stick in the water and you look at it from the surface, it looks bended.
Fact: In water, the Field Of View of your lens will be reduced.
This may be useful in certain cases -mainly for macrophotography- but it reduces your image size, so you need to go further to have the same image magnification factor than on land. When you go further underwater, you add particles between the flat port and the subject. The much closer you get to the subject, the best it is.
FOV in air [°]
20
30
40
50
60
70
80
90
100
110
120
FOV in water [°]
15.0
22.4
29.8
37.1
44.2
51.1
57.8
64.2
70.3
76.0
81.3
FOV : Field Of View
Using the same lens your field of view in air decrease while underwater, with a flat port.
Distortion
Fact: When using a flat port, the refraction induces an image distortion.
Thanks to Fabio Menna for this diagram
When you use wide angle lenses (above a FOV of 60°), the distortion become a real issue. The image quality significantly decreases, especially in the corners. (A good example is those sports cameras, with a field of view around 120° it’s a real mistake to use a flat port.)
There are physical formulas to calculate all you need about refraction but in a basic way for our concerns we can simply remember that the field of view of your camera lens will be reduced when you use it underwater with a flat port and that you will have significant distortion of the image if your FOV is wider than 60°.
Subspace Pictures has a variety of flat ports, usually used with macro lenses.
Using a dome port:
Refraction
Using a dome port, all the light coming in reach the dome with a right angle, we have no refraction. The Field Of View of your camera lens is the same underwater than on land.
And no refraction means no distortion.
Other issue appears. The dome port acts as a spherical diopter, a divergent lens.
Underwater we will have a curve virtual image closer to the camera lens, meaning your focus distance will be much closer than in air, this depending in the radius of your dome port. You need to have a good lens / dome port combination to have good results.
Subspace Pictures designs are always based on fully calculate underwater optics with formulas not described in this summary, this is our expertise area. We explain basic facts here to help understand some of the specificities of underwater images.
Note about dome ports :
There is confusion about dome port Cuted diameter and the Optical diameter. What you need is an Optical diameter adapted to your camera lens. So when we talk about underwater optics, our 7, 8, 9, 12 inches domes we are talking about the Optical diameter.
The Cuted diameter is where you decided to cut your half hemispherical dome to keep only the part you needed.
It depends of the Field Of View of your camera lens.
As instance, the dome port below is made for a FOV of 130° maximum.
An half hemispherical dome port is adapted to a 180° FOV.
Ergonomic Housings
As every diver knows, carrying out underwater actions requires skill and concentration. Concerning the underwater shooting, it is therefore essential that the housing is built according to this demanding and complex environment. For this, Subspace Pictures calculates the buoyancy of its systems and think of and the arrangement of each function of the housing according to the simplest and most intuitive movements for the user.
Initially, the experience as a Subspace Pictures diver allows us to adapt the design according to the points presented above.
Moreover, this includes user feedback, so handling the housing is as intuitive and pragmatic as possible.
Pressure tests / Destructive tests
In the process of validation of our designs, we perform pressure tests,
we also go until destructive tests to improve our knowlege.
Deep housings custom designed dome port destructive tests.
We also test our camera and monitor underwater housings, always useful to increase knowledge, evolves our research and development database as well as for the scuba divers safety.
