1 DON'T OVERDO IT
When a camera housing that has never been looked after floods, no one, least of all the owner, is surprised. But many camera housings at the other extreme of care also flood. I dont know why it leaked. I always did all the maintenance on it, is the woeful cry of the bemused owner.
The mistake that many owners make is to do all this maintenance too often. The camera gets so much TLC that it is literally loved to death.
Each time a housing is opened, there is potential to make a mistake in closing it, and suffer a subsequent leak.
If I dont need to change lens, battery or memory card, my camera housing stays closed.
Though this article is aimed mainly at users of compact cameras, the same principles apply to more sophisticated systems. Using big memory cards and batteries on UK wreck-diving, which is all wide-angle, my main camera system often stays closed for four or five days at a time. This saves time fiddling and reduces the risk of mistakes, though I still have to change flash batteries every two or three dives.
When a housing is opened, do you really need to take the main O-ring out of its groove and grease it Every time it comes out, there is a risk of damaging the O-ring.
Every time it goes back in, there is a risk of inadvertently trapping dirt, hair or fluff behind it.
Most of the time, an O-ring can be inspected in place and a judgment made as to whether it needs cleaning and greasing, or whether it can be left alone.
Most of the time, a gentle wipe round with a spit-wetted finger of the O-ring and the surface against which it mates is all that is necessary.

2 TEST IN THE RINSE-TANK...
One of the best uses for a rinse-tank is not for rinsing cameras, but to test for obvious leaks before going diving. A short dip, turning it at various angles while you watch for bubbles, then out it comes.
Having looked for bubbles in the tank, we can now look for water inside the housing, by tilting it so that any drips show against a transparent part of the housing like the lens port. This simple check could identify a critical leak, before you find out the hard way at 30m.
If a rinse-tank is not available, a camera can be held in the sea for a minute or two for a similar, though less convenient, check. Finally, just as a technical diver often pauses at the start of a dive to check for bubbles at 5m, I like to make a similar check of my camera.

3 ...BUT DONT LEAVE IT LYING THERE!
hspace=5 A rinse tank is somewhere to slosh a camera housing for a quick rinse, not a safe place to leave it unattended.
I cringe at the number of times I see cameras abandoned in the rinse-tank by their owners.
Leaks are often worse when there is no water pressure to hold the housing together. If a minor leak on a dive goes unnoticed, leaving a camera in the tank for another 30 minutes could turn it into a fatal flood.
Even if there is not latent problem from the dive, all those camera housings rattling and bashing together in a rinse-tank cant be good for them.
Plastic bits get scratched. Latches could be knocked loose and pop a housing open.
My usual procedure is to hold the camera beneath the surface in the rinse-tank with one hand, while waggling each of the controls a few times to displace salt water with fresh water.

4 SUNSHINE BURNS
hspace=5 This applies to all cameras, not just those in underwater housings. Leaving a camera in any position where the lens catches the sun can focus that sunlight inside the camera and burn it.
Just as using a magnifying glass to focus sunlight onto paper can start a fire, the same could be happening inside your camera.
Cameras and housings are best left in the shade. If this is impractical, make sure that the lens is pointing away from the sun, and ideally cover the housing with a cloth or towel. I have even been known to prop my fins over my camera to create shade, when there is no other option.

5 RINSE BEFORE OPENING
hspace=5 When a camera housing comes out of the sea, trapped water will evaporate to leave small deposits of salt in all the nooks and crannies.
A quick rinse as soon as possible, either in a tank or gently under a shower, will get rid of the worst of this, but may not always be possible.
Later in the day, the sea water has dried and it is time to open the camera housing to change batteries, download the memory card or whatever else you need to do. In the process, any dried salt on the outside of the housing can end up sticking to the O-ring or getting inside the housing.
Dried salt also gets onto the photographers hands, to be transferred to the camera, memory-card or battery.
I like to give a camera housing a quick sluice down with a shower or bottle of water, or even a hose, as long as the pressure is not too great. Dont aim the water directly into the main seal.
I then dry the critical bits with a towel - including myself - then make sure that no fluff is left on the housing before opening it up.

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6 OPEN THE BOX
Some manufacturers advise us to open housings with the door downwards, so that any water on the O-ring cannot drip inside. The trouble is that while drips cannot fall in, the camera itself could fall out and be damaged.
If you need to open a camera housing with the door downwards, do it just above a folded towel, so that the camera has a soft landing if it falls out.
Before opening, wipe the outside again quickly to make sure there are no drips about to cause a problem. Then have an old, clean handkerchief to hand to wipe round quickly and catch any drips as soon as it is opened.
The reason for a well-washed old handkerchief is that it is unlikely to leave stray fibres that could cause a subsequent leak. Paper towels and tissues must be avoided at all costs. When damp, they soon shed fibres.

7 POPPING O-RINGS
When O-rings need servicing, the easiest way to extract them from their groove is to squeeze them along it until a loop pops up.
Be careful not to push too much and stretch the O-ring, and then be careful not to damage it while you are easing it clear of the housing.
Sometimes a shim of soft plastic such as the end of a cable tie can help to ease an O-ring from its groove. Any O-ring lifted with sharp implements such as a knife, needle, pin or dental pick could now contain hidden damage and is best replaced rather than reused.
Even worse, a dangerous tool could scratch the groove and cause a leak. Soft camera O-rings are far more susceptible to damage than hard cylinder O-rings.

8 THERE COULD BE A CATCH
hspace=5 When the housing for my pocket digital camera arrived, the O-ring was dry and needed greasing.
I pulled it from the groove, but didnt notice a metal pin that the catch pushed up to release the door. This pinched the O-ring and cut a small segment from it as I pulled it out.
Before I could use the housing, I had to buy a new main O-ring. In fact I bought three of them, because there was a minimum order value.
Now aware of the pin behind the catch, I know to move the catch back, and have not damaged any O-rings since. I still have two spares sitting in my repair kit.



9 CLEANING AND GREASING O-RINGS
Once an O-ring is out of its groove, the first step is to clean any existing grease away, together with any dirt stuck to it. Warm soapy water works best. I slosh the O-ring about, wipe it with my fingers until no trace of the original grease remains, then rinse it again and hang it to dry.
At a push, if no washing facilities are available, I wipe off most of the grease before licking the O-ring clean.
A tongue is wonderfully sensitive for picking off the last few specks of salt or dirt.
Last time I wrote about cleaning O-rings this way, a reader wrote to warn that silicone grease can be carcinogenic. But then, so are many substances, and its not as if I am eating it regularly in large quantities!
I leave re-greasing O-rings until they are ready to go back in their groove. That way there is less chance of the newly greased ring gathering dirt while it waits.
Remember, the purpose of the grease is to lubricate a moving O-ring, and that excess grease will only attract dirt. The main O-ring of a camera needs the benefit of lubrication only as the housing is being opened and closed.
The smallest blob of grease will do the job, wiped along the O-ring with fingers until the entire ring is slick and slippery, but with no clots of excess.

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10 CLEANING GROOVES
There is little point servicing an O-ring unless the groove is also cleaned. My favourite tool for this is a cotton-bud, and I keep a handful in my camera bag.
I lick the end to wet it slightly, then run it gently along the groove while rotating it to wipe out any old grease and dirt.
On a plastic housing, you need to be careful not to push any dirt along the groove and scratch it.
A slight reservation: the cotton bud could shed very fine fibres into the groove, so the groove needs to be inspected thoroughly before the O-ring is put back in. An alternative tool is a corner of the handkerchief we used earlier.
As well as cleaning the groove, dont forget the other surface against which the O-ring mates. This also needs gently wiping clean, ideally along the surface rather than across, so that if it does pick up invisible scratches they are along rather than across the O-ring, and wont act as a bridge for water to leak past.

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11 EASE IT IN GENTLY
hspace=5 O-rings need to be carefully eased into place, so as not to damage them or pick up dirt in the process.
With a long and complicated groove, be careful to get it evenly into the groove all round without any bunches of surplus because it has been over-stretched elsewhere.
As a final check, I gently run a spit-wetted finger along the O-ring, as well as the surface against which it mates, to feel for any irregularities before closing the housing.
Never force a housing closed.
If it won't close easily, it may be that an obstruction needs to be sorted out.


12 TO DESICCATE OR NOT
hspace=5 One of the most frustrating things for a photographer is to be halfway down to the wreck before noticing that inside the camera housing the lens port is fogged.
It could be a leak, but more likely the housing was closed in a damp atmosphere, then the glass at the front becomes the coldest surface for the humid air inside to condense onto.
Plastic housings tend to be considerably more susceptible to this than aluminium.
The usual solution is to tuck a small sachet of desiccant or silica gel inside the housing, ideally closing it all up the night before the dive so that the atmosphere inside is thoroughly dried.
I make up sachets from a bulk container of silica gel stitched into the remains of an old shirt.
This carries its own risk. Leave the corner of the sachet poking out, and it could be the cause of a leak.
Use an old sachet, and it will actually release humidity into the housing and cause fogging.
The desiccant absorbs moisture from the atmosphere whenever it is not inside the housing, so I keep the sachets individually double-wrapped in Zip Lock bags, and then stored inside an old film canister. Barring leaks, a single sachet will last a two-week trip.
On the other hand, in a dry climate such as Egypts, especially when shore-based, condensation is never a problem and desiccant is not needed.

hspace=5 13 TEST IT
With everything back together and ready to go diving, I always take a test shot in a shaded place, so I can see flashguns fire and everything working.
I often end up photographing my camera bag or shoe, then delete the picture to make sure it doesn't find its way onto anything that gets submitted to the magazine!