Do Ikelites fog?

I'd put it a different way. It's not equalization that's causing condensation. It's that the air immediately around the cold surface is cooling below it's dew point, the air in that local pocket has greater than 100% humidity.

We are saying the same thing. The air in the local pocket has greater than 100% humidity *because* of the equalization.

I tihnk it has changed, but only in the pocket of air right around the cold surface.

Yep, we are saying the same thing.

you lost me there... I think you are saying that if the housing is a good insulator, you'll get a larger thermal gradient, and then you are more likely to get condensation?

Assuming there is an X degree temperature differential between the air inside the housing, and the housing itself, then an object with a greater thermal coefficient is going to require more heat transfer for the temperatures to equalize. That is a pretty basic physics statement that we can both agree on.

FWIW, I also agree with your general assertion that *all other factors remaining unchanged*, raising the temperature of the air inside and then cooling it again should not cause condensation.

However, theory and fact do differ in this case. I can vouch for my S70 housing fogging up after I've taken a few shots with the camera and onboard flash - and this is warm waters where the temperature difference between the water and the air is only a handful of degrees (in fact, when I prepare the housing, the air temperature is LESS than the water temperature when I am diving).

As such, I am not sure whether or not all other factors do remain unchanged. Due to convection and radiation, all the air particles are heating up due to the flash; however, heat loss is primarily due to conduction and limited to the air pocket that is touching the surface of the housing.

If this is so, not only would the air pocket touching the housing surface lose more heat, but also the moisture particles in that air pocket (I dont remember off-hand my college physics, but I suspect that cooler water particles may have a greater propensity to coalesce into droplets... although even if that isnt the case, the argument still holds).

So the heat gain and heat loss functions are not symmetrical... which would explain the inconsistency.

Anyway, this is my theory.

Vandit

However, theory and fact do differ in this case.  I can vouch for my S70 housing fogging up after I've taken a few shots with the camera and onboard flash - and this is warm waters where the temperature difference between the water and the air is only a handful of degrees (in fact, when I prepare the housing, the air temperature is LESS than the water temperature when I am diving).

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In that case, there should be no way your camera can fog. No way. If temp only goes up, humidity can only go down...if moisture content remains the same. I don't think it does, I think moisture content goes up because the added heat frees moisture that was in your camera.

As such, I am not sure whether or not all other factors do remain unchanged.  Due to convection and radiation, all the air particles are heating up due to the flash; however, heat loss is primarily due to conduction and limited to the air pocket that is touching the surface of the housing. 

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I think heat loss doesn't matter, as long as you stay above the dew point. And you are above the dew point, you started in a colder room with no condensation. So I think a factor is changing: moisture content is rising.

If this is so, not only would the air pocket touching the housing surface lose more heat, but also the moisture particles in that air pocket (I dont remember off-hand my college physics, but I suspect that cooler water particles may have a greater propensity to coalesce into droplets... although even if that isnt the case, the argument still holds).

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You are right, a cooler air/water mixture is more likely to coalesce, or condense... if the mixture cools to the dew point temp.

So the heat gain and heat loss functions are not symmetrical... which would explain the inconsistency. 

 

Anyway, this is my theory.

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Ok, I understand what you are saying... but still disagree. I still think the inconsistency is you are adding moisture by distilling water out of your camera by heating it.

think anyone but us is left reading this thread? I've enjoyed it.

define "us".

In that case, there should be no way your camera can fog. No way.

Heh, I wish you'd tell it that

Ok, I understand what you are saying... but still disagree. I still think the inconsistency is you are adding moisture by distilling water out of your camera by heating it.

That is also a possibility. I have to admit, I dont remember enough to be categorically sure one way or the other.

I'll email a friend who is a theoretical physicist (with disturbing fantasies about beating up Stephen Hawking, whom he calls a hack), and ask him what the deal is.

think anyone but us is left reading this thread? I've enjoyed it.

You mean we didnt impress the chicks? Oh hell. Back to the drawing board. And yes, it has been enjoyable, thank you for the discussion and safe diving to you.

Regards,

Vandit

if you don't trust theorists, we can test this. Take your housing, with no camera, and leave it in the sun. If you're right, it will fog. If I'm right, it won't. Now do it with your camera in there. If I'm right, and there is enough moisture in your camera, and conditions are right (I'm not weaseling, those ifs are real), it will fog. if I do it, it won't fog, my camera is dry, I always use healthy desicant, with an indicator strip so I know it's good.

Let me give you another example. My local water is low 50's. As I decend and my camera and housing are cooling, I get condensation on the port, if I have a lot of moisture in the housing. As I ascend, the camera is the slowest thing to warm up. Parts of the camera, internally, will be at 50 for quite a while: the batteries, sealed parts of the lens, metal frame, any bigger chunks that are slow to warm. So I get condensation inside the camera, where I can't see it. The camera drys out slowly over time, but if I make another dive too soon, there is moisture in there that can be distilled out.

Now, your water is hopefully not 50 degrees. But the cycle still happens. There is a time when your camera is the coldest thing in the housing, or even cold after you take it out of the housing, and your camera is still grabbing some moisture. Not as much as mine would, but some.

And then that moisture is there to distill out later when you heat the camera up.

So use desiccant to grab any free moisture, and keep the water out of your camera.

The actual spot where the vapor decides to condense is also important. If you have an aluminum housing with an acrylic port then the vapor will condense on the Al and leave your port clear. No problem there.

The problem I see a lot is w/ consumer housings that have a plastic housing with a glass lens port. The vapor condenses on the glass port :-(

Ikelite housings are acrylic w/ acrylic ports, so no problem there.

Cheers

James

unless the port is thinner acrylic.

But you also have metal buttons and rods, they cool fastest and probably get all the condensation.

I always use healthy desicant, with an indicator strip so I know it's good.

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Hello Roger, where do you get that kind of desicant?

All that really matters is trying to keep everything the same temperature. We need not worry about realive humidity or dew point or whatever. Condensation can occur with any camera, any housing or in any environment under the right conditions. My Nexus never fogs but I got a small spot of condensation on the glass viewfinder window because the housing came out of 59 deg water & it sat in 80 deg sun (directly on the viewfinder) for several minutes before I could rescue it. The result of temperature difference. Once everything equilized again no condensation. Use the silica packs if you think you need them. You will need them more in a plastic housing which is a better thermal insulator than metal. Your housing will always have some moisture content unless you backfill it with dry nitrogen (or equivalent). Sorry - but I just can't see moisture trapped in the camera being the cause of these problems. I've dove 4 times a day for a month in a tropical location, working on the rig in a non A/C room, without any condensation problem underwater. Just a couple of fogged viewfinder windows as discribed above. As soon as temperatures equalized it disappeared. For those that like numbers heres the relative thermal conductivity for several materials: Polycarbonate 0.2, Water 0.6, Aluminum 235.0, Acrylic 0.1, Glass 1.5 (same units for all values - thats the really confusing part). The greater the numeric difference between materials the quicker thermal equalization will occur - alum/water - real fast, acrylic/water real slow. Believe what you will - I'm going diving

jcclink, I'm still gonna disagree with you. Read the links I posted above. Condensation isn't due to temperature differences. It's due to air cooling to below its dew point. Keeping things the same temperature doesn't matter at all. You need to keep important things (your camera, your port) above the dew point temperature. You can do that by keeping temp high or moisture content low.

Any other physicist or chemists or even engineers out there or am I alone on this one?

Davichin: I can't remember where I got mine. I've had them a while. You want the ones in the white tyvek packets, they are called minipax. Not all of them have the clear window strip for the indicator. I like the ones that do. Sometimes my packets go for a long time, many trips, but other times, one trip and they are saturated. I recharge them myself, they last a while. I only get rid of them when I overheat them and melt the tyvek.

Don't get the clear plastic packets. They absorb much more slowly, too slowly to be any good in a housing.

get this kind:

http://www.packworld.com/cds_search.html?r...rm=(desiccants)

how to recharge. Note that the tyvek melts at 250°F.

http://www.sorbentsystems.com/desiccant_regeneration.html

So that would preclude my diving in Antarctica? A cold surface is required. If you have thermal equilibrium there is no cold surface available. I guess we will just have to agree to disagree on this one. Fortunately fogging is basically a non issue for me. I do agree with trying to keep moisture content low, but that is easier said than done, especially in tropical locations.

You might also check out

http://preservesmart.com/products.htm#SilicaGelDesiccants

for silica packs.

Let's say your housing is in thermal equilibrium at 90°F and 90% humidity.

You lower it to 30°F on a dive in antartica. You let it come to equilibrium.

You don't think there's condensation? (frost, really).

I do.

How do you explain the graph in the middle of this page?

http://hyperphysics.phy-astr.gsu.edu/hbase...tic/relhum.html

same stuff, no graph:

http://www.usatoday.com/weather/wrelhum.htm

I say you can have a temperature differential and get no condensation as long as no temp in the system is below the dew point. I think you are saying that you will get condensation anytime you don't have thermal equilibrium (or only one greater than a certain amount?) and as long as you do have thermal equilibrium, you get no condensation, even if you are below the dew point. Dew point is irrelevant to condensation. Right?

Ikelite housings are acrylic w/ acrylic ports, so no problem there.

It was my understanding that Ikelite flat ports are glass.

However, I've never had an issue with fogging - ever.

jcclink, I'm still gonna disagree with you. Read the links I posted above. Condensation isn't due to temperature differences. It's due to air cooling to below its dew point. Keeping things the same temperature doesn't matter at all. You need to keep important things (your camera, your port) above the dew point temperature. You can do that by keeping temp high or moisture content low.

 

Any other physicist or chemists or even engineers out there or am I alone on this one?

 

Davichin: I can't remember where I got mine. I've had them a while. You want the ones in the white tyvek packets, they are called minipax. Not all of them have the clear window strip for the indicator. I like the ones that do. Sometimes my packets go for a long time, many trips, but other times, one trip and they are saturated. I recharge them myself, they last a while. I only get rid of them when I overheat them and melt the tyvek.

 

Don't get the clear plastic packets. They absorb much more slowly, too slowly to be any good in a housing.

 

get this kind:

http://www.packworld.com/cds_search.html?r...rm=(desiccants)

 

how to recharge. Note that the tyvek melts at 250°F.

http://www.sorbentsystems.com/desiccant_regeneration.html

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Thank you very much the desicant info, RogerC. I am an engineer too, and I think you are right. I don´ know about he humidity in the camera (I guess I don´t want o believe it!!! ) but I think that when condensation occurs in the surface more subject to it and you are underwater, the amount of energy required o re-evaporate the drops is no easy to find anymore and that´s why, I think, sometimes he fog does not disappear...

The difference between a metal housing and a plastic one when you go from warm air to cold water is that the metal housing body will cool faster than the plastic or glass port, so the condensation should be on the metal surface and not port surface. That may not be the case with a plastic housing.

I don't know if that's really a problem in practice. I've talked to a few people who use Ike housings in Monterey (50F/10C water) and they told me that they don't have fogging problems.

Wikipedia has a somewhat helpful (well, assuming you know or can determine a few variables) formula for dew point (relating to condensation).

Source: http://en.wikipedia.org/wiki/Dew_point

 

Here is a formula to calculate the dew point in degrees Celsius to within ±0.4 °C. It is valid for

 

0 °C

0.01

0 °C

 

where

 

T = temperature in degrees Celsius

RH = is the relative humidity as a fraction (not percent)

Td = the dew point temperature to be calculated

 

The formula is:

 

where

 

and

 

a = 17.27

b = 237.7 °C

ln is the natural logarithm.

Current temperature when you seal the housing wouldn't be difficult to determine, but relative humidity could be depending on where you are.