[PSUBS-MAILIST] camera

Sat Apr 11 12:05:05 EDT 2020

While I have not yet personally tried this (I'll be conducting experiments
like this once I get my pressure test tank built, able to generate
controlled hydraulic pressures), what Hank mentioned may work. This will
depend entirely on the camera you intend to use. I have not been following
this thread, so please forgive me if I'm speaking about things in
ignorance.
Because lenses are involved, you'd have to be sure to get the mineral oil
throughout everywhere - including in between the lenses of the camera
(depending on the camera you're using). If the camera has mechanical zoom,
then you won't be able to use it because there is multiple lenses which
move and change position relative to each other. It would literally be like
a miniature hydraulic cylinder in there, with pistons moving in opposite
directions - the mechanics of the camera just wouldn't be able to do it
because it's trying to fight hydraulic pressures.
Also, mineral oil has a different density than air or water, and so the
optics will get thrown off because the lenses are designed to work in air.
The index of refraction in water, oil and air are all different - which is
why your eyes don't work well underwater. So the mineral oil is going to
throw off the focal length of the lenses. If it's a pinhole camera, I think
you might be alright, but I haven't done the math and the physics, just so
you know. lol This may change in refraction may cause bizarre effects like
a permanent zoom or permanent out of focus. And that's the part I haven't
done the math and physics on, nor the experiments. I could be wrong on
this, but I don't believe any ROV's have oil-filled camera housings, and I
expect it's for these reasons.
However, with regards to the electronics of the camera itself, the mineral
oil is an insulator (as you guys already know obviously) so there won't be
electronic interference, however the hydrostatic pressure of the water is
being transferred to the camera housing, which is compressing and
transferring hydrostatic pressure to the camera parts through the mineral
oil - including the electronics. Most electronics can withstand enormous
pressures so you're probably alright. Just keep it in mind - again it
depends on the camera you intend to use, and the components that camera
has. You'll notice a lot of deep submersible ROV designers literally fly by
the seat of their pants on this one: they just stick the electronic
components they want to use into a pressure test vessel and crank the
pressure until they hear something crack.  :D
Most microchips wind up with an air pocket inside their plastic housing,
overtop the silicone chip itself. CCD's have their silicone chip surface
exposed, but I'm unsure about possible air cavities behind the silicone
chip. Any cavities can collapse under pressure or the liquid can leach
along the leads into the plastic housing. In both cases, it probably
wouldn't matter if you've immersed it all in mineral oil because it's an
insulator. However, if the mineral oil gets enough hydrostatic pressure to
force oil along the leads and into the air pocket inside the microchip, it
can fracture the chip case when the outside pressure is removed because now
the interior has excessive pressure stored up inside. Again, this may or
may not cause a problem if it's immersed in oil. You might just wind up
with a fully-functioning microchip that has a cracked case.
Lots of electronics for deep ROV's are literally just potted or painted
circuitboards out in the open water and just relying on the physical
strength of the components to withstand the extreme hydrostatic pressure.

What I have seen suggested with ROV cameras though is optical-clarity
potting (i.e., clear casting acrylic). Again, whether or not you could do
this would depend entirely on the camera - if it's got a moveable lens,
then you've got a problem because the cast plastic would lock the lens.
You'd have to figure out some way of casting everything but leaving an air
space around the lens portion.

Okay, enough random thoughts for now.
Ian

On Sat, Apr 11, 2020 at 11:09 AM Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> That could be interesting  ,  the mineral oil I use is crystal clear.
>
> Brian
>
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: hank pronk via Personal_Submersibles <
> personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> Subject: [PSUBS-MAILIST] camera
> Date: Sat, 11 Apr 2020 11:21:18 +0000 (UTC)
>
> Brian, I have thought about putting a camera in an oil filled housing like
> I do with my lights.  You could put the camera in an acrylic tube same as
> the light.  Fill with clear oil and the view would not be distorted because
> it is oil filled.  I am convinced the camera would take the pressure just
> fine.  A worthwhile experiment, because you would avoid making complicated
> 1atm housings.
> Hank
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