Go Pro Fogging

[Marty Cerven]

Correct, but here's the thing: the air inside the camera case isn't "warm and moist". It is whatever it was when the case was closed, which is the same no matter how much heat the camera generates. Only after the case has been closed (and the air has been trapped) the air will heat up from the camera. No moisture is added. In such a scenario, increased temperature will decrease the relative humidity of the air, in other words the air will become warmer and drier, which will increase its capability to evaporate any potential water drops. This is also why AC'd air is drier: cooling down the air will make a lot of the water vapour condensate, so after it warms back up to the temperature it had before there's less moisture in the air (lower relative humidity) than it had before. Warm it up even more and it becomes even drier, which is why I'm pretty sure that a camera generating a lot of heat is actually beneficial towards fogging issues.

This is why closing in a cool dry environment will help you by begining with a low moisture content in the cooler air. This will mean there is less moisture that can condense due to the temperature difference, as you heat up the air inside the closed housing any moisture will form on the coolest surface (typicaly a glass lens) as condensation. If you have less moisture in the housing this will need a larger temperature difference to occur and this is caused by the inside air heating relative to the outside air/water temp. The fogging is caused by the moisture created by condensation as it evaporates inside the hot air of the housing, not the heating of the air on its own. This is where the confusion may come from as its not the heating of the air on its own but relative to the outside temperature that causes condensation.

So closing in front of the ac will reduce the chance of this happening but using dessicant packs also will take all the moisture out of the air making condensation impossible at any temperature inside the closed housing. I always use my methods and have never had fogging, without dessicant packs going into cool water it will fog up very quickly. Seeing this works for me 100% of the time I dont see the point of avoiding ant fog techniques with the risk of wasting all footage due to fogging/condensation.

Diving in cooler waters will always show up these issues much faster then diving warmer waters where you may get away with doing nothing at times. Water here is 9c to 21c through the year but Ive also dived 31c water in asia with the same results.

 

[archiebald]

Sorry to jump in here, I have read the thread and quite honestly there is a huge lack of understanding on the part of several posters.

Warm air versus cool air and the heating by the camera is all a load of nonsense.

The thing which is vitally important and no one seems to have mentioned is "dewpoint temperature". The key thing is that the dewpoint temperature of the air inside the case must at all times be lower than the actual temperature of the case body caused by the surrounding water. Since the lens is glass and the rest of the body is plastic it is the lens that will be affected first because glass has a higher thermal conductivity than plastics.

The air temperature inside the case, whether due to the temperature when closed or the temperature rise from camera operation has zero to do with the fogging issue.

Many people get confused by dewpoint temperature because a typical air conditioned room environment might have an air temperature of example 23degC and a dewpoint temperature of 10degC. i.e there are two different "temperatures"

A simple definition of dewpoint temperature is "the temperature at which water vapor suspended in air will condense onto a cold surface into visible droplets". As such, "dewpoint temperature" is not actually a temperature but a measure of absolute moisture content of the air. This is quite different from Relative Humidity which is a variable that is calculated from a combination of dewpoint temperature and air temperature.

So in the room example above, if you had a glass of beer at 11degC then condensation will NOT appear on the surface because the dewpoint temperature of the air is LOWER than the glass, but a glass of beer at 9degC WILL show light condensation. It wouldn't make any difference if the air temperature in the room went up or down - as long as the dewpoint temperature (i.e. dryness of the air) remains the same then no change to condensation build-up will occur. I is the dewpoint temperature that is important. Take the glasses of beer outside in a tropical climate and both will show heavy condensation because the dewpoint temperature outside might be 10 to 15 degrees HIGHER than the cold surface of the glass, but not because the air is warmer.

In a camera housing, if you close the case in front of an air conditioner where the air is dryer, then the dewpoint of the air trapped inside the case will be low and have a lesser chance of condensation. The fact that the air from the air conditioner is also cool is just a red herring - the key thing is the dewpoint of the air.

Once the camera is sealed, the number of water molecules present inside (and hence the dewpoint temperature of the air ) cannot change whatever the camera does to raise the air temperature. If anything, the heat of the camera helps to provide a defogging assistance by artificially keeping the inner surface of the case just a little bit warmer. In the case of the GoPro being so small, the heat loss to the outside is so great that the case rapidly chills off. This is a function of surface area versus volume. The ratio of surface area to volume increases as the volume becomes lower. Hence, the GoPro loses heat to a faster degree than larger housings so the inner surface of the case drops below the dewpoint temperature of the air inside and condensation starts.

The only way around this is to;
1. Start with a lower dewpoint temperature (that means dryer air) air conditioned air, or scuba air will provide this
2. Use desiccant to pull the dewpoint temperature lower.

 

[CajunDiva]

Another thing that hasn't been mentioned, but is important to point out...

Don't leave the GoPro running all the time during your dive. Just turn it on and use it when there are subjects you specifically want to shoot, then turn it back off. This may help prevent heat build-up.

FWIW, I used the GoPro anti-fog strips and didn't have a bit of trouble.

 

[archiebald]

Another thing that hasn't been mentioned, but is important to point out...

Don't leave the GoPro running all the time during your dive. Just turn it on and use it when there are subjects you specifically want to shoot, then turn it back off. This may help prevent heat build-up.

FWIW, I used the GoPro anti-fog strips and didn't have a bit of trouble.

Heat build up doesn't cause fogging. If the air is dry enough (low dewpoint) then nothing else matters. The desiccant is keeping the dewpoint low, hence you experience no fogging.

 

[Marty Cerven]

Ok so heat has nothing to do with it lol, get 2 housings put dessicant in one and none in the other close them both. Nothing will happen while the inside and outside temperature remain the same add heat inside the housing or cool the outside and condensation will occur in the one without dessicant. How do you explain that in your theory that heat has no effect?

If you use desiccant then this will take out enough moisture from inside the housing that condensation cant occur but the other will if the outside temp drops enough or inside heats up significantly.

 

[archiebald]

Ok so heat has nothing to do with it lol, get 2 housings put dessicant in one and none in the other close them both. Nothing will happen while the inside and outside temperature remain the same add heat inside the housing or cool the outside and condensation will occur in the one without dessicant. How do you explain that in your theory that heat has no effect?

If you use desiccant then this will take out enough moisture from inside the housing that condensation cant occur but the other will if the outside temp drops enough or inside heats up significantly.

BTW, it's "desiccant", not "dessicant" and you are mixing things up. I only said heat on the inside will not increase fogging.

Actually, when you put active desiccant in a casing then seal it up something IS happening but it is invisible. The air trapped in the casing will become dryer down to a new equilibrium point.

Ignoring desiccant for a moment, simply adding heat on the inside will do nothing to change the moisture content of an enclosed casing. How can it? The same number of water molecules will always be present in the trapped air so the dewpoint temperature of that air remains constant. Remember, dewpoint represents an absolute value of the water content, not a relative value as in RH%. In fact adding a heat source inside will help to warm the inner surface of the casing so that it might just keep the surface above the internal air dewpoint temperature and stave off condensation a little longer when the case is put into cold water.

When you place a camera inside the casing and operate it, you are not simply adding heat. You have also added moisture from within the camera itself which is being driven out of the camera and into the casing thereby actually raising the dewpoint temperature of the air in the case. To an outside observer this might make it look like the heat source has caused the fogging but the truth is that the camera has "contaminated" the case with its own additional moisture content. I would recommend also conditioning the camera before placing it inside the casing. I always leave the camera in the open case in front of an air conditioner for at least 30 minutes prior to sealing it.

Cooling the outside of the casing on the other hand, has a profound effect because effectively you are lowering the inner surface of the casing temperature and if you continue to lower it below the dewpoint temperature of the air trapped inside , then condensation will start to appear on the inner surface.

The reason why the one with desiccant does not fog up (until much cooler) is because you have reduced the dewpoint of the air in that casing. That is what desiccant does. It absorbs the free moisture in the air inside the case so that you can drive the casing surface temperature lower before condensation will start to appear. But even adding desiccant will not work if the outside temperature is low enough - there are practical limits.

Sorry if I am coming across as a know it all - that is not my intention but I work in the engineering plastics industry and give training courses to customers on the use of desiccant drying systems working to a dewpoint of -40degC and below. Dewpoint temperature is quite difficult to get your head around at first - the majority of people don't understand it.

 

[Marty Cerven]

If the due point stays the same even with a rising temperature inside the housing then the extra moisture drawn out of the camera would have to explain this. I have seen housings fog up when they are left in the sun on a hot day with no anti fogging method used so this is the only way that could be explained. I assumed the rising temperature must have been raising the due point but looks like I was wrong.

Sorry about my typo its not a word I use too often, I don't see that as a huge issue but maybe you could proof read all my posts . Many of my posts are sent from my phone which has some random auto correct and its a bugger to correct longer posts inside the mobile browser so you may have to excuse some of my spelling or point out all my errors.

I still see using desiccant as the best option this will absorb any moisture in the air and from inside the camera itself and has always worked. Combine this with sealing the housing in a cool dry environment and you should never have any issues.

If you reduce the relative humidity enough without saturating the desiccant inside the housing there is just no possible way of getting condensation at the temperatures we are using the cameras at. Even in high humidity tropical climates the water temperature will be much higher so taking most of that moisture out of the air in the housing wont allow it to reach the dew point.

 

[archiebald]

Marty,
Sorry if it wasn't clear but I was not picking up on your posts originally.

In my work, we are dealing with controlling moisture content down to 0.0025% (or 25 parts per million) using desiccant drying systems.

I totally agree with your last post, I have seen people complaining about fogging but they don't use desiccant. I posted this on the GoPro forum recently but it is worthwhile repeating here.

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Archie's golden rules for preventing fogging in any underwater camera case are as follows;

1. Use a diving or skiing goggle type antifog solution on the inside of the front dome. Washing liquid or good old saliva are also acceptable substitutes.
2. Leave the open case and camera directly in front of an air conditioner set on maximum cooling for at least 30 minutes prior to closing it up. Household, hotel room or car - doesn't really matter.
3. Failing that, a warm (not too hot) hair dryer for 10 minutes may help.
4. In winter on a bright and crisp day it might actually be better to seal the case outside rather than in a hot stuffy room or car.
5. Install the GoPro or equivalent desiccant packs. They can be regenerated in an oven so they are very economical. If you haven't got them yet , don't be a cheapskate - they will make a world of difference.
6. Never open the case outdoors in hot humid conditions until you have finished filming for the day. If you have to change the battery or card then open the case for the shortest possible time and if possible under the conditions listed in rules 2, 3 and 4.
7. When not actually shooting, keep the camera / case out of direct sunlight.
8. In snow conditions, wipe any snow off the case, especially the lens as often as possible.


Rules 2,3 and 4 are all about reducing the dewpoint temperature of the air in the case as far as possible before sealing it.

If anyone would like to add to this list, please feel free but following these will be 99.9% certain to prevent fogging woes.
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[OH2OD]

Thanks for this informative thread. I just got a GoPro and backscatter case for a June trip to Bonaire.
I ordered the desiccant packs with camera and plan to use them.

 

[diversteve]

I went to the auto store down the street and got a double pack of RainEx. One pack was RainEx original, and the other was "RainEx Anti-Fog" for the inside of car windshields. We used the Mako flat lense, treated the inside with the anti-fog and the outside with the original. Worked like a charm! No fogging on a 1-hour long dive with the Hero2 in 62 degree water.

Video for reference.

fwiw even Rain-X doesn't recommend using their products on optical ports as it will cause them to cloud over time since it apparently etches slightly. There's an old thread about it here: http://www.scubaboard.com/forums/tips-techniques/74077-droplets-lense-housing.html - post #9 - and another one either here or on another board where a Rain-X mfr's rep agreed. Some people have posted that Novus products work w/o damage.