DSLR Housing Design Safety Factors

Does anyone have first hand knowledge of the static design safety factor for the various DSLR housings? I think that it would be very interesting to all of us to know how robust housings really are.

Common commerical pressure vessel hydros are 1.3 to 1.5 max operating pressure.

Engineering tell's me we have around 2 for safety factor, our depth rating is 300ft/90m standard but we routinely upgrade our housing to 425ft/130m for technical divers and know for a fact that they have pushed the enveloppe beyond that point both on the Brittanic wreck and on oil rig platforms. Bottom line is we have yet to succed in crushing one in any pressurized environment, substainable or not.

One thing to consider is that IMO there are two depth rating type, one is how deep you can go and still be in able to use the housing with working controls that do not stick, the second is how deep can you safely go with the equipment before risking a catastrophic flood due to equipment collapse. when we upgrade a housing to 425ft/130m we basically make the controls stiffer so that they won't bottom out and stick at greater depth.

I honestly do not know what is the failure point of our housing is, but knows the safety factor its way beyond the limit of "normal" technical diving and is at least beyond the 500ft mark.

Hope that helps.

In order to find out you would need a test system capable of withstanding something in excess of 15bar (probably considerably in excess) as I know that Seacam too, like Aquatica, have been used to well beyond their 'rating' of 80m (something around 150m if I remember correctly) or a potential rating of 120m in the case of the strengthened Superdome (which has a heavier, 2mm thicker than normal, backplate to prevent flexing).

It also depends what you define as a failure. Two problems exist. As Viz'art states, firstly the controls will tighten up (I know for example that one of my customers found that whilst camera controls remained operable beyond 100m, the flash units he was using locked up their controls and could not be adjusted), and secondly, leaking due to deformation/component failure (such as a port glass failure). I also have a friend whose housing imploded at just over 40m, many years ago, probably due to age/stress 'hardening' of the plastic from which it was constructed - it was old and had carried out many dives and this and similar housings had operated well beyond this depth when new - so material/age/construction is also a factor. A scratch in a port may also provide an area which can fail under load )think about marking out glass to break it along a line) so using a damaged port at significant pressure is probably best avoided too.

My suspicion is that many/most manufacturer's 'rated' depths are based upon testing pressure limitations rather than anything else.

My suspicion is that many/most manufacturer's 'rated' depths are based upon testing pressure limitations rather than anything else.

Agree, that and the desired control weight, from playing with an 'uprated' housing that had stronger springs fitted to the controls it was not pleasant to use at the surface ( nor I would assume in the depth range where I normally take pictures ).

It was really hard work pushing those buttons!

Probably great at 120m - I didn't care to go and find out....

Paul C

Good question!

The thing about the controls on a housing is that there are a few types. Because buttons are basically "straight through" the pressure pushes them in and can make them useless. Shafts that go through the housing and turn may still work though.

The way that the Brazilians do static collapse used to be to throw something overboard and listen carefully w/ a hydrophone. When you hear the "crump" you know it collapsed ;-) Anyone want to try that w/ their housing?

My guess would probably be 2x the rating or slightly less if using a dome port.

Cheers

James

...My guess would probably be 2x the rating or slightly less if using a dome port.

Color me ignorant (I'm a EE, so you know I know diddly about mechanical thingies) but I'd have thought a dome does pretty good against external pressure. Wouldn't a flat port be expected to fail first, or is it more an issue of total surface area exposed?

Color me ignorant (I'm a EE, so you know I know diddly about mechanical thingies) but I'd have thought a dome does pretty good against external pressure. Wouldn't a flat port be expected to fail first, or is it more an issue of total surface area exposed?

You are not ignorant, these are issues seldom discussed on forum, and you are right will fair better a dome, due to its natural spherical shape, than any given flat port... of equal thickness that is, which is why typically a flat port will have a somewhat thicker lens than a dome port if it is to be rated for the same depth.

interesting also is that many of us stick to the port as the weakest link, actually acrylic window port with multiple buttons are likely to fail way faster than a port, the thickness of the thinnest part of the acrylic window port is what count, you couls have a 1/2" acrylic port with holes for buttons, but if two buttons holes are a mere 1/8" apart, the your port has only 1/8" of pressure resisting thickness.

Acrylic_window.pdf

Yeah, well the front of a dome is round - but what about the back ;-) If the dome curvature mounts directly to the housing like an old A4 housing then it's super strong, but most have a flat plate on the back which is the weak link.

And yes, I do design for 2000psi hydrostatic pressure from time to time ;-)

Cheers

James

James:

Thanks for the answer. I didn't think of the annular flat on the 'backside' of the dome as a crush point against external pressure. Flat, large surface area, large hole in middle equating to less stiffness as well. Makes sense!!