How do you adjust focus and exposure underwater? Do you use a viewfinder?
What are the physics of the situation that would make a PVC housing more likely to fog than an aluminum one? Fogging has mainly to do with humidiy of the air in the housing and the material of the dome and the temperature gradient between the water touching and the air inside. Fogging - when it occurs in either al or PVC housings is pretty easy to cure using $3 desiccant packs.
FYI with over a year of experience with epic-m and epic x overheating hasn't been an issue, with either PVC or AL. I have never cared whether the customers chose PVC or aluminum - I make more money when they go aluminum, but there are some advantages to the lighter PVC body when it comes to dealing with heavier lenses and ports, as well as lighting systems and not having to use bouyancy tubes which is often the case with the metal housings (and of couse shipping or traveling). BTW I have offered all of the PVC buyers the option for up to six months for full Tradein For the aluminum - just pay the difference - and none have taken us up on it.
----- Edit note: This previously had a portion questioning Jon's expertise, but I had mistakenly confused him with another poster that had previously posted some incorrect information and didn't seem to have much experience.
my sincere apologies to Jon Shaw ---------
On a nicer note - Liked your work, good on ya with those rays - know hard it is to get those shots. And some of the schooling fish shots were pretty sweet also.
You can easily setup the Aquavideo housing for redvolts quad module, v-bricks or Anton-Bauer -all have been used and housing size is the same - you can change from one to the other anytime. I like the quad module because It came with the epic-x and it is 1 less wire to deal with. The new XL redvolts provide over 180 watt hours with the quad module.
You are absolutely correct with your observations :)
The physics of condensation is through water vapor cooling and compressing that produces liquid.
Plastic (PVC) housings conduct heat substantially less than metal, causing increased temperature and pressure inside the housing as compared to metal housings. For that reason, they are more prone to condensation.
Thermal conductivity of PVC is only 0.19. Glass is about 1.0. aluminium is massive 250 [W/(m.K)]
Aluminium will transfer the heat out of the housing much quicker than glass. But, in case of a PVC housing, it is the glass that would be much better heat conductor...and source of condensation at the same time.
Additionally, for strength reasons, PVC housings are much thicker than metal. This further inhibits the heat transfer.
Tensile strength of PVC is up to 60MPa. Aluminium alloys can go as high as 300Mpa. Titanium goes to about 1000Mpa.
There is, however, secondary reason of condensation inside plastic (PVC) housings. PVC has relatively high water absorption ratio. All organic polymeric materials will absorb moisture to some extent. Commonly PVC has water absorption in a range up to 0.4%. Metals have none. When PVC is warmed up, it releases additional water vapour inside the housing, which is then cooled by the glass port and can cause condensation more readily than a metal housing.
hope this helps
The prosumer and consumer PVC housings used acrylic ports so not much thermal conductivity difference there. In terms of our housings for Epic and Red 1 - i.e. those relevant to most Redusers - and as I mentioned in the Bubble blowers discussion, they have an aluminum front plate with a pretty large surface area that provides substantial cooling area.
BTW doesn't titanium have a thermal conductivity quite low for a metal? something like 5.8? which is a lot closer to PVC than Aluminum.
What is your and Jon's actual experience with PVC and aluminum housings with same cameras, size housing, and conditions, that would actually give evidence of there being a significant difference in tendency to fog? Because I have that experience, as do many of my customers, and it hasn't been significant. And again, if one believes it is significant, buy the aluminum version - I make both - and make more money on the aluminum - I just don't like to see you guys spreading inaccurate FUD.
My practical experience with PVC housings mainly comes from dissapointed Redusers writing to me saying that their Aquavideo housings leak and that the manufacturer does not respond to their messages.
Just stating the facts, not spreading any FUD.
The great thing about understanding physics and engineering based on material data and proper calculations is that you do not need to have negative experience with a bad design when you can have a positive one with a good one instead. That's the purpose of engineering.
Besides, I was respponding to Jon, not to the arrogant, disrespectful and incorrect post that Hastings made above.
Jon is one of the best underwater film makers I've ever met. He is a commercial diver, an experienced instructor and one of the friendliest and most helpful person I've had a pleasure to work with. He was my number #1 choice to take my first DeepX prototype for the first dive when I fructured my ankle and was unable to dive. I trust him and his feedback entirely. I have made numerous design changes based on his feedback alone.
The footage that Jon showed here speaks for itself. There is no need to be arrogant, question his experience or hijack his thread in a desperate attempt to flog a leaky sewer pipe to an unsuspecting Reduser. It's just plain rude.
Respect is a two way street.
Not sure I should even respond to that (post 47), but I would certainly like to know who that is and rectify the situation, if it hasn't been already.
Pawel, I hope you don't have any problems with your business, because I don't wish it on anyone, but I don't think there are any manufacturers that have sold more than a few housings that have a perfect record. I have personal knowledge of cases of leaks from every manufacture that people are likely to have heard of, and a few you probably haven't heard of. However, I have never publicly "outed" any of them because not only did I not have all the facts or both sides of the story, but I just don't think it is the right thing to do. It seems that you think I have disparaged your housing, but I'm pretty sure that virtually all of my criticisms were about the limitations of the Nikonos 15mm on an Epic sensor which is much smaller than the 36x24mm film size for which it was designed, and therefore provides a much narrower field of view than its designers intended. And it is based not just on my opinion but the widely accepted principles of underwater photography held by every professional I know and every book I've ever seen on the subject. I don't think I ever knocked your housing per se and I think in fact I have complimented the design of the housing itself, it seems well and cleverly engineered for what you were trying to do (which again - sorry I can't resist - I proposed in 2007). If I've said in relation to your housing itself, it was in response to things you or someone like Jon said that has not aligned with my experience or seemed to point up some flaw in the methods used by myself, Gates, etc. that I don't think were accurate.
I've tried to explain some of the differences, but I offer both aluminum and PVC at very reasonable prices. I don't have much experience with Titanium since it never seemed to be necessary or worth the price differential in material and machining cost, and that seems to be the industry consensus vs. aluminum, but I'm not knocking it either.
I would like to make a sincere apology to Jon Shaw, I confused him with an another Australian poster with the same initials that I remembered some pretty bad posts that were obviously promoting Pawel's agenda and had a number of incorrect things in it that seemed to indicate a lack of knowledge - for example this quote: "It uses nikonos lenses which can be interchanged underwater and are easy to buy and low cost."
Again, Jon I'm sorry - it was a case of mistaken identity and you didn't deserve my questioning your knowledge or expertise. While I stand by my statement that overheating on epic is not a substantial problem - I thought it was the other guy just taking a cheap shot.
I probably shouldn't have made it personal anyway - I will just say that the tenor of Pawel's posts for a long time has pushed me, and I think a lot of the bubble blowers, to the limit and I've let my own level of discourse be degraded.
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