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Stuart Keasley

Member Since 23 Aug 2008
Offline Last Active Today, 06:30 AM

#346299 Subal S7Q Housing for the Odyssey 7Q

Posted by Stuart Keasley on 15 April 2014 - 10:52 PM

Looks like my prayers have been answered


My interest is to pair up with the FS700, however Convergent Design have also said the 7Q will support the Sony A7S, and presumably therefore the GH4.

#346097 BMPCC underwater filming setting

Posted by Stuart Keasley on 12 April 2014 - 11:51 PM

That device is to work on a flat surface. If you go diving on rocks you won't have that. And if you go on sand you can have 4-5-7 20 legs but stability comes out of balance not planting the legs in the sand as if it was an anchor. Even sand contains living organisms and should make sure your impact on the environment is as little as possible. That's my perspective at least. Results matter but after am sure am not demanding more than needed out of the seabed

From the Edelkrone web site:

"Works great on uneven surfaces, adapts to any surface"

A quadpod has no issue with an uneven surface. It has adjustable legs.

I'm with you, in that I'd rather work with a tripod. But it's a preference thing, Edmond has gone a different route, he's happy with it and is getting good results.

#346084 BMPCC underwater filming setting

Posted by Stuart Keasley on 12 April 2014 - 03:06 PM

Quadpods are more stable and stronger but can take longer to set up.

Tripods are still stable, and are a lot quicker to work with.

You've got some stunning results Edmond, which us really all that matters ;)

#345812 Physically small intervalometer

Posted by Stuart Keasley on 07 April 2014 - 09:53 PM

I'd go with Magic Lantern. Yes, there are risks, however has anyone ever heard anything ever going wrong (when using just timelapse)

And yes, I've used it on a 5d mkii

#345774 Malta

Posted by Stuart Keasley on 07 April 2014 - 04:52 AM

Thank you Stuart ,yes i have been told the same thing (enigmatic) about mauri but due to the problems with organisation (%50 my fault) i couldnt do it. I wish i can dive to the places you recoment one day

Just for a tease, filmed quite a while ago now, but here's the Southwold


#345578 Vacuum leak detector question

Posted by Stuart Keasley on 03 April 2014 - 07:59 AM

Obviously this needs some extensive testing.  I suggest we send a dedicated and unbiased researcher (that would be me) to the Caribbean for a grueling two-week regimen of test dives.  I will thoroughly document the testing process and advise you of the results upon my return home.  In regard to funding this research, please send a PM and I will send you my paypal address. 
Now about this Scotch Mist; does adding lemon peel to a nice whisky really create an enjoyable beverage?  I have my doubts but could probably experiment with that as well during the above two-week research project.  No additional funding would be required for this.  Plus, I could watch for condensation on my glass as I go from an air-conditioned room to the patio and supplement the fogging data.

Can't help with funding, but I'm very happy to supply a pressure cooker (possibly a head to put in it to check for results ;)), along with a small tub of water, some ice cubes and a copy of Nuffield A-level Physics test book (1987 edition), all obviously essential elements for your tests :D

#345562 Vacuum leak detector question

Posted by Stuart Keasley on 03 April 2014 - 12:49 AM

Aluminum conduces heat much more than glass or acrylic so in general terms if any condensation occurs it will be on the walls of the housing and not on the port or the LCD.


Obviously the many people who experienced condensation on their glass port in an aluminium housing were just seeing scotch mist.







Edited: Admin

#345531 Vacuum leak detector question

Posted by Stuart Keasley on 02 April 2014 - 10:59 AM

Sorry about that Draq!   I will try to clearly answer the 2 questions posted in this thread using what little expertise I have in the area as a hyperbaric physician.  I will not get drawn into a pettifoggery once again.
Your question if the negative pressure generated by the Nauticam system will make it less likely to flood -the answer is yes, because the o-ring is sucked into the mating surfaces of the housing, preventing blow-by. 
watboy, your question if an additional benefit of a vacuum system  would be that it would eliminate condensation issues , the answer is no.  It will greatly decrease them though.  If you close your housing at 30°C and 75% relative humidity, condensation will form when the housing wall reaches 25°C.  Under the same conditions, If you pump the housing down negative 10 inches Hg,  condensation will form when the housing wall reaches 18°C.  Starting conditions will certainly modify the results, but not the manner in which you can calculate the benefit. The explanation is below.
Condensation forms at the dew point which is when relative humidity (RH)= 100%
RH= partial pressure of water vapor (PW) / vapor pressure of water (VP) at a given temp.
Vapor pressure of water at a given temp. (VP) is independent of pressure
When you decrease the pressure by 10 inches Hg, you are decreasing the pressure inside the housing by 30%
Following Dalton's law, decreasing the housing pressure by 30% will decrease the partial pressure of water (PW) by 30% once the temperature equilibrates.  Therefore, relative humidity will decrease by 30%
So starting at 30°C and 1atm and a RH of 75%, pumping the housing down to .7atm will yield a RH of 67.5% once the housing equilibrates with the 30°C ambient temp.
Using the dew point curve we know that at 30°C and 75% RH  the dew point = 25°C
Using  the dew point curve we know that at 30°C and  67.5% RH the dew point = 18°C
So after vacuum there will be a 7°C degree difference in how cold you have to get the housing wall before condensate will form.
I will be happy to answer any questions not originating from Interceptor.

Thanks, good to have a nice summary to cut through all the posture and waffle.

#345517 Vacuum leak detector question

Posted by Stuart Keasley on 02 April 2014 - 04:14 AM

Congratulations, you've proved that water requires heat before it will evaporate.

You could get a Nobel prize for that.

As for your other comment, you misunderstand me, it's your tenacity fir being wrong that has beaten me.

#345475 Vacuum leak detector question

Posted by Stuart Keasley on 01 April 2014 - 07:34 AM

Actually no, the camera heating up inside the housing will DECREASE condensation in the camera.  The hot camera heating up the inside of the camera will decrease the realtive humidity (meaning that any condensate that has formed on the walls of the housing will find it easier to evaporate).  You have used the term "jdew point numerous times, this term just means 100% relative humidity.

There is a few where things will react differently


- Interior of the camera heats up and generates a temperature differential between the inside of the lens element and the air inside the housing. In this instance, you'll see condensation appearing on the inside element of the lens instead of the inside of the dome port

- If there has been water ingress into the housing during assembly, e.g if some particles of rain dropped in, as the inside of the housing heats up, the pools of water evaporate and then increase the relative humidity inside the housing, dew point therefore increases in response.


However in general:


- When you assemble the housing the inside and outside temperatures are the same.

- When you enter the water, the outside temperature will be (generally) colder

- The dome port will slowly reduce temperature to match the water, the interior surface of the dome port therefore becomes cold.


If the interior temperature of the dome port is at the dew point of the relative humidity of the air inside, condensation will appear. If you're lucky, the heat generated by the camera may be sufficient enough to heat up the air inside the housing, and the interior surface of the dome port, making the condensation disappear (in much the same way as you would blow hot air on a windscreen to demist it)


However, whatever is at play, it's all about the dew point.


That's the way I understand it, anyway ;)

#345450 Vacuum leak detector question

Posted by Stuart Keasley on 01 April 2014 - 01:58 AM


Your educational principles are a bit dated if you think putting someone in a corner to think matters is the way forward.


(Metaphorically) going into a quiet corner, without distraction and taking time to think things through is a very effective way of gaining understanding. I suspect you didn't finally get to this conclusion whilst sat on your sofa watching a psychedelic thrash metal performance on the TV ;)



I have non problems admitting when am wrong. 



Odd, that you still haven't done so then.



Like you I said that the dew point that is a temperature would go increase with pressure. 


No, you initially said quiet the opposite.



High pressure means drier air in fact when you breath compressed air you feel lack of moisture as the dew point is pushed further down

This is incorrect, the opposite of what you've now said in terms of dew point, and also incorrect in it's very basis. Also, compressed air is dry for no other reason that it has been filtered during the compression process. 


You then changed your tune


As in a higher pressure environment you have a higher dew point it feels drier at the same temperature and lower pressure it feels wetter.




Compressing air increases the dew point temperature and has a drying effect



However you've continued to say that compressing air makes it drier. This is not true, compressing air actually increases the relative humidity, it will feel wetter.



And the point is exactly that one once you set up your recompression chamber it is dry in side because you are pressurizing things



Again, incorrect. Recompression chambers don't get drier when you pressurise them. In fact, during the pressurisation process a fog develops inside the chamber (I'm no expert, but would imagine that this is a combination of both increased pressure and increased temperature)


On a side note, there's a cave in Tonga Vavau Group called Mariner's Cave. Access is from the seaward side of a cliff face via a 15 metre swim through at a depth of 5 metres. There's a big chamber inside, with breathable air.


If you visit the cave around midday, the sun shines in from the north and lights up the inside with an aquamarine blue. That in itself is quite spectacular. But if there's any sort of swell, the surface level of the water inside the cave slowly rises and falls. With each rise, an aquamarine fog forms, each fall, the fog dissipates again. It's quite eerily beautiful, almost as though the cave is breathing.


All caused by the volume reducing and therefore pressure increasing on the air inside the cave.


Unfortunately I didn't have a camera when I was there, and none of the videos I can find do it justice :(


The matters geot confused when your speak about relative humidity as actually what changes is not the % of moisture but the total number of particles of dry air and vapour. Which means now air can hold more moisture before it condenses. I could not work this out myself as the weather station measures the % and therefore reported no changes. The dew point is the absolute humidity not the relative and therefore this now makes sense to me. So I agree that of you pump air out the number of particles reduces and so does the vapour which means that the temperature to which those particles would condense is lower than if I had not created vacuum. Now the fact that if I set the housing outdoor I get 84% humidity and if I do it indoor I get 55% does seem far more important in terms of avoiding condensation but it would seem that if you create a low vacuum you may go in water a tad colder (don't know how to possibly quantify this) before your housing fogs. Now back to work


But no matter, big hooray, we got there in the end (shame you didn't read post 76 properly, it said exactly this is nice simple language) :)



don't know how to possibly quantify this


A lot of those links I put up will do the calculation for you. For instance, you've stated an outdoor humidity of 84%, let's put you somewhere nice and warm(ish) with a temperature of 24 C


Using the link you put up, and filling in the values (http://www.oxywise.c...ou-calculate-it)


The dew point at atmospheric (1 bara) is 19.47 degrees.

If you now suck out 5 Hg (or .16 bar) and so reduce the internal pressure to 0.84 bara the dewpoint now becomes 16.74.


So the interior temperature of the housing would need to drop almost 3 degrees lower for condensation to occur once you'd used your vacuum pump. I'd say that's pretty significant.



#345446 Vacuum leak detector question

Posted by Stuart Keasley on 31 March 2014 - 11:54 PM

Here's a dew point calculator, pop in the dew point at ambient and the line pressure, it will then tell you the dew point at the new pressure


Here's another calculator, with a plain as day statement at the very start

Dew point changes as pressure changes (and vice-versa). Therefore, if you know an air streams dew point at a given pressure, then change the pressure, the dew point will change.


Even the link you shared earlier on has a calculator on it that clearly shows a change in air pressure will have an effect on the dew point ie the temperature at which condensation will occur.


This is quite interesting, although a bit more complex. Read it carefully, if you start to misinterpret it to mean that removing air from a housing won't reduce dew point, then you've taken a wrong turn. Go back, and start again.


With all of this stuff, all that matters is that pressure changes. It doesn't matter whether the pressure change is effected by increasing or reducing volume on a sealed object, or by introducing or removing gas from a rigid sealed object, the net effect is exactly the same, you are merely changing different parameters within the equation.

#345444 Vacuum leak detector question

Posted by Stuart Keasley on 31 March 2014 - 10:10 PM

If this was a closed system being compressed and decompressed I would not have any issue in agreeing that pressure increase changes humidity levels.
However this is the other way around you are decreasing pressure by pumping matter out you are not applying pressure on the same amount of air.

Please, go and stand in a corner, face the wall and think about what you've just said here.

Reducing the pressure using a pump is, by definition, decompression.

The only difference is that we are taking the housing pressure below ambient pressure instead of naturally allowing it to equalise with ambient pressure. However Dalton's Law still applies.

If this was something really easy to understand and to demonstrate I would have worked it out by now just by doing experiments instead it seems a much more complex matter

If you're having difficulties understanding, perhaps better to say that instead of doggedly insisting that everyone else is wrong. This isn't a matter if opinion, it's relatively basic physics, defined by some if the laws of physics.

As I said earlier, I can see where you made the initial mistake, I initially made exactly the same mistake and also got it wrong.

as in fact you don't find any literature where vacuum is using on its own to remove moisture there is always a condenser and vacuum is just used to clean

I have posted two documents that state what we are explaining to you quite clearly.

#345414 Vacuum leak detector question

Posted by Stuart Keasley on 31 March 2014 - 10:32 AM

Wow, didn't think my comment would have caused this much debate.

I'm not sure that debate is the right word for it. More increasingly frustrated attempts to try and get someone to understand and accept that 2 + 2 = 4, not 0.

#345402 Vacuum leak detector question

Posted by Stuart Keasley on 31 March 2014 - 07:42 AM

Yes that's exactly correct and looking at your Wikipedia paragraph 2 At temperatures below the dew point, water will leave the air. As you are moving the dew point down you are making more likely to have a wet environment. Phew it did take a long time!!!

I'm not entirely sure what you're saying here, sincerely hope you are finally agreeing with what we've been trying to explain to you and the reams of information that has been shared ;)