underwater videographer course | equipment | underwater video housings
Underwater Video Housing
This section assists you in choosing an underwater housing for your video camera.
Housing Construction
Flexible Clear Plastic
Pic of EWA marine housing
At the most basic level, flexible clear PVC housings are available for video cameras. These are sealed with a special zip that keeps them watertight. They usually have a flat glass or optical plastic window on the front which attaches to the camera to keep it aligned with the lens.
Such housings can only be taken to a few meters deep, and because of the relatively flimsy construction, one has to be very careful to avoid puncturing them. However they are relatively inexpensive and they do have the advantage of allowing access to all of the camera's controls.
If you're intending just to shoot shallow, such as while snorkelling, then one of these "glorified plastic bags" might suit you. They are also often successfully used for shooting surfing videos. I have also heard of them being used by non-diving cameraman for expensive pro cameras in very shallow-water situations when an underwater cameraman or housing was not available or over the budget.
EWA MarineLINK make some well-liked flexible housings, as well as rain covers. Aquapac http://www.aquapac.net/ukstore/camcorder-case-br-code-465-1892-0.html Scuba thingyLINK also make them.
O-Ring Sealing
Before we look at the different rigid housing constructions, it's worth noting that all of them are sealed with O-rings. O-rings are used to seal the main door, around the port and controls, and also in static seals such as where body components are permanently joined together.
pic of o-ring
O-rings are usually made from nitrile, which is a black rubber-like material. It is very resilient, meaning it likes to return to its original shape. It is available in different degrees of hardness.
There are three main ways to form an O-ring seal. These are in a facial groove, in a radial groove, and in a chamfer.
pic of cross sectional ways of sealing an o-ring: chamfer, radial groove, facial groove. Show before and after sealing.
Dual O-ring systems are often used to reduce the chance of leaks. Amphibico's housing doors use 2 O-rings in radial grooves. My Light &Motion ports have an O-ring in a radial groove in combination with one on in a facial groove. My Seapro housing's door had a radial O-ring and a chamfer O-ring.
Pics of combinations of o-ring seals: 2 x radial, radial + facial, radial + chamfer
A light coating of silicone grease is applied to O-rings to lubricate them and help them sit in the correct position. See the maintenanceLINK section.
O-rings are usually circular in cross-section, but X section(CHECK PROPER NAME) O-rings are also available. My Seapro housing used these for its control shafts. When under pressure this type of O-ring is designed to tighten down harder on the sealing surfaces than conventional circular cross section O-rings.
Pic of cross section of X section O-rings
Occasionally natural rubberCHECK O-rings are used. Gates uses these for the main door of their housings. These are softer than nitrile O-rings and are only really suitable for a facial seal. It is essential that they are not greased at all, as this degrades the rubber.
Rust
Rust is the oxidisation of steel. It is a big problem in the marine environment but can be prevented by using stainless steel, in which Nickel and Chromium are added to the steel alloy to prevent rusting. These should be included in at least the ratio 18:8 to make a good, rust-free grade for latches and other hardware on your housing. It's important to note that there are different grades of "stainless" steel, including some that will still rust. A so-called stainless steel that still rusts can be useful for your dive knife as it can often be made very sharp, but it is definitely not a good material for your housing's hardware.
Aluminium Oxidisation
Aluminium also corrodes by oxidising. The surface of raw aluminium quickly combines with the oxygen in air, and the aluminium oxide forms a dull, protective layer. The corrosion does not continue to "eat" into the metal like rust does. Nevertheless there are marine-grade aluminium alloys available that are suitable for use in seawater. Housing manufacturers sometimes specify "aerospace" grades which are also strong. Aluminium alloy can be treated with hard anodising after machining to give a tough, corrosion-proof finish. Aluminium can also be painted but an etching primer must be used first to cut through the oxide layer and stop the paint later peeling off.
Galvanic Corrosion
Copy from my wetpixel post
Galvanic corrosion is a particular challenge for the underwater housing manufacturers. Every metal or metal alloy has its own innate electric potential which can be measured in volts. When metals of different electrical potential come into contact with each other, or close to each other in the presence of an electrolyte, they form an electrical cell or "battery". Electrons pass from the cathodic metal to the anodic metal and the cathodic metal gradually corrodes.
Unfortunately sea water is an excellent electrolyte, and aluminium and stainless steel have very different electrical potentials. This means that if the housing manufacturers just screw stainless fittings into aluminium housing body parts, the aluminium will quite rapidly corrode, becoming powdery white and either swelling up or just getting washed away.
It is difficult to use the same metal throughout because for example aluminium is not really strong enough for latches and stainless steel is not really suitable for a housing body. But there are grades of aluminium that are strong enough to make screws out of. There are aluminium screws in my Light & Motion Bluefin housing's handles for example.
One way to counter the galvanic corrosion is to use strong "engineering"plastics for components that might otherwise be made of metal.
Another way is to attach to the cathodic metal a piece of a third metal of an even higher(?) cathodic electric potential. This third metal is "sacrificial" and reacts with the anodic metal in preference to the other metal, thereby saving the other metal. Gates use this approach by screwing a thick zinc washer to the base of their housings.
Rigid Machined Plastic Pipe
Pic of Aquavideo housing
A common low-cost way of making a housing it to machine it out of large diameter, thick-walled, cylindrical plastic pipe such as ABS or PVC. A cylinder makes a very good pressure vessel, so in theory the walls can be thinner than if the housing has flat walls.
There is quite a high capital cost in setting up for manufacturing this type of housing, because a large lathe and milling machine are needed, but once this plant is in place the tooling costs for supporting different models of camera are low. It is simply mostly a matter of adjusting pipe diameter and length, and then customising the controls to fit the camera. This means that new cameras can be housed quite quickly, or that cameras can be housed that the major housing manufacturers have decided not to support.
In these housings it's typical for the rear door to be made of clear rigid plastic such as acrylic or polycarbonate so that the inside of the housing can be seen. The front of the housing is typically plastic or aluminium with a port set into it, or just a flat sheet of plastic acting as a window.
There is no corrosion problem with these housings, as there can be with metal housings.
One disadvantage of the cylindrical construction when used with mechanical controls can be a long distance between the housing wall and the camera's controls. Machining tolerances are critical for correct alignment of the controls and to prevent excess play in the control shaft which might lead to leaks.
The designer's control of the final buoyancy of the housing is somewhat limited using the cylindrical construction.
Cross section sketch of distance
AquavideoLINK are one company who make these type of housings.
Injection Molded Plastic
pic
If the housing manufacturer expects a high volume of sales then it can be cost effective to injection mold housings. Injection mold tools are expensive to manufacture so this is not a method for short production runs.
This type of housing typically consists of 2 clear moldings, a front "shell" and a rear "shell", with a side hinge and latches to close the housing. A clear glass or plastic port is fitted into the front. Usually the housing leaves room for the camcorder's flip-out LCD screen to be open inside the housing.
The video camera manufacturers themselves tend to make their housings this way. JVC has a range of injection molded housings for their small camcorders.
Equinox (or is it Epoque) is quite a new manufacturer who injection mold underwater video housings. They make a housing this way for the Sanyo Xacti camcorder.
It is vital that the injection molding process is tightly controlled or else distortion or even cracks can be introduced.
Resin Cast Plastic
Pic of Ikelite housing
Polyurethane resin is cast by mixing two chemical components and pouring the mixture into a mold at room temperature, where it sets solid. The critical surfaces of the molding such are later machined to size.
Set-up costs are quite low, and lead times quite short, as the molds do not need to withstand the heat and pressure of injection molding tools.
It is necessary for the walls to be quite thick as the material is not as strong as, for example, injection molded acrylic or polycarbonate.
Resin casting is how Ikelite make their housings, and they are the only manufacturer I know of who use this technique. Incidentally Dive Rite also use resin castings for their light battery housings.
Machined Solid Aluminium
It is common for housings to be machined out of solid aluminium.
The simplest construction is to machine the housing out of cylindrical aluminium stock. My Greenaway Seapro housing was made this way. John Heike of Phi Phi Scuba made a number of underwater housings machined from old aluminium scuba tanks. The cost was low and they were used successfully by a team of day trip videographers.
Gates and others machine their housings out of solid aluminium.
There are many different grades of aluminium and it is naturally important to use one that is highly resistant to corrosion. CHECK GATES GRADE AEROSPACE??
Cast Metal
Casting is the process of pouring hot molten metal into a mold, or "die", where is solidifies.
Pressure die-casting has parallels with injection molding, and is not suitable for short production runs because the die is very expensive.
Short production runs can be manufactured using sand casting. A fabricated replica of the housing known as the "pattern" is surrounded by special sand to produce a mold, and then molten metal is poured into this mold. It is surprising how accurately thin-walled sand castings can be made by an experienced die caster.
Aluminium, zinc, or even magnesium are all metals that could be used to cast underwater video housings. Once the metal has been cast the cosmetic surfaces are linished ready for finishing, and the sealing surfaces and control details are accurately machined. There is less waste and potentially time saved over machining out of solid metal.
However the design of the body castings and control of the casting process are absolutely vital to prevent porosity in the housing that could lead to leaks, especially if any voids or pores in the casting occur next to machined surfaces.
Some of Amphibico's housings are made of cast aluminium, one of them being the VX2000 housing.
Investment casting???
Extrusion
Extruding is the process of squeezing molten metal through a 2-dimensional die to produce a length of metal with a uniform cross section. It's a bit like squeezing icing sugar through a star-shaped nozzle. Aluminium window frames are made this way.
The main body of Top Dawg and Light and Motion Stingray housings are manufactured out of an aluminium extrusion. The critical surfaces of the extrusion are machined for accuracy.
Mechanical versus Electronic Control
There are housings that allow mechanical access to the camera's controls. There are housings that allow electronic access to the camera's controls. And there are hybrid housings that allow a mixture of mechanical and electronic access. Then there are housings that allow both mechanical and electronic access to the same control. The relative merits of mechanical versus electronic control of underwater housings is an area constantly debated by videographers, photographers and manufacturers.
In a mechanically controlled housing, the video camera's controls are typically operated by stainless steel rods that penetrate the housing body. A knob, lever or button on the exterior is used to rotate, push or pull the rod (or some combination of these actions in succession). On the end of the rod is usually a thinner section of stainless steel that is bent to precisely operate the camera's control.
In an electronically controlled housing, signals are sent to the camera's controls through a cable plugged into the video camera's LANC socket. Control buttons are usually operated by the fingers and thumbs at the top of the housing's handles, or sometimes on the housing body. The housing controls usually require their own batteries, but electro-mechanical inductionCHECK can also be used instead, as in the Top Dawg and Light and Motion Stingray housings.
The big advantage that mechanical controls have over electronic controls is reliability. No matter how much the reliability of electronic controls improves, they are still more prone to failure in the marine environment than mechanical controls. Electronic controls fail at some point in their life, often without any particular explanation. If the components don't fail then cables do. And if a housing does leak, then the electronic components inside are usually destroyed if they get wet, especially with salt water. If you are on a dive trip and don't have the spare parts or service expertise required, this usually signals the end of shooting video for that trip. On the other hand a leaky mechanical housing can often be washed out and used again, once the source of the leak (e.g. A wrongly assembled O-ring) is rectified.
Another advantage of mechanical housings is that they can be built for just about any camera, whereas electronic housings need the camera to have a LANC socket. Sony are the only company that regularly incorporates the LANC socket in the video cameras, although the recent Canon XXX was another. As a result the leading manufacturers of mechanically controlled housings such as Gates and Ikelite support cameras by Canon, Panasonic and others as well as Sony. The leading electronic housing manufacturers such as Amphibico, Light & Motion and Sea & Sea tend to only support Sony.
One inherent advantage that electronic controls have over mechanical controls is that fewer holes need to be machined through the housing body, and so there is less chance of leaks. The other big advantage is that the position of the control is more flexible. A button can be put more or less where the designer wants it. Conversely the position of the controls on a mechanical housing is dictated to a certain extent by the position of the control on the camera and it's relationship with the construction of the housing.
Certain controls lend themselves to mechanical operation and certain controls lend themselves to electronic operation. For example I would always prefer to focus using a big mechanical rotary knob that operates my camera's focus ring using a 90-degree gear. I find this gives faster and more accurate control than pressing electronic "far" and "near" focus buttons which tend to overshoot or undershoot or limit the speed of focus change. But conversely I like sometimes like to switch between auto and manual focus modes in the middle of a shot, and I like to be able to do this with no wobbles and keeping both hands in their normal postiion on the handles. A carefully-placed electronic button makes this possible but I have found that mechanical controls can take some fiddling to operate, which inevitably induces wobbles.
Other Factors to Consider
Service in the field
Access to manual white balance is a big factor
Don't overstretch your budget
Underwater Video Camera Housing Manufacturers
Ikelite
Good value
generally reliable
mechanical controls
Crazing
Crack on Martin's
No corrosion between plastic and steel
Gates
Very reliable
Excellent customer service
Great lenses by Fathom
Corrosion between latches and body
Buoyancy tubes
Amphibico
Well known in the industry e.g. BBC
Common to hire one
Some reliability problems - Rob monitor, leak I had
Vignetting
Service not as good as Gates?
Light and Motion
Problems in past
Not as reliable due to electronic controls
Mention my Stingray and problems
Mention my Bluefin and generally good service
Good lenses
Good buoyancy
Service patchy, not as good as Gates
Sea and Sea
Very strong on stills cameras
Aquavideo
Quick to design and manufacture
Custom housings
USVH
asfasdf
Ocean thingy (yellow ones like USVH)
dsdf
Seatool
asdas
Sealux
asdfd
Sony
asdfasdf
Equinox
rust, poor service
Aquatica
New entry. Excellent stills housings
< back to video cameras | underwater video housings| forward to ports and lenses >
